The Troposphere

The Stratosphere and Ozone Layer

The Mesosphere

Ionosphere

The structure of the ionosphere is strongly influenced by the charged particle wind from the Sun (solar wind), which is in turn governed by the level of Solar activity. One measure of the structure of the ionosphere is the free electron density, which is an indicator of the degree of ionization.

Mid-Level Clouds
Cloud types include: altocumulus, altostratus.

-Typically appear between 6,500 to 20,000 feet (2,000 to 6,000 meters). Because of their lower altitudes, they are composed primarily of water droplets, however, they can also be composed of ice crystals when temperatures are cold enough.

Low-Level Clouds
Cloud types include: nimbostratus and stratocumulus.

-Mostly composed of water droplets since their bases generally lie below 6,500 feet (2,000 meters). However, when temperatures are cold enough, these clouds may also contain ice particles and snow.

Clouds with Vertical Development
Cloud types include: fair weather cumulus and cumulonimbus.

-The cumulus cloud is generated most commonly through either thermal convection or frontal lifting, these clouds can grow to heights in excess of 39,000 feet (12,000 meters), releasing incredible amounts of energy through the condensation of water vapor within the cloud itself.

Other Cloud Types
Cloud types include:
Contrails (also known as a condensation trail, is a cirrus-like trail of condensed water vapor often resembling the tail of a kite. Contrails are produced at high altitudes where extremely cold temperatures freeze water droplets in a matter of seconds before they can evaporate. Often exhaust fumes from a jet engine. If the surrounding air is cold enough, a state of saturation is attained and ice crystals develop, producing a contrail.), Billow clouds ( Billow clouds are created from instability associated with air flows having marked vertical shear and weak thermal stratification), mammatus (Mammatus are pouch-like cloud structures and a rare example of clouds in sinking air, usually seen after the worst of a thunderstorm has passed), orographic (When air is confronted by a mountain, it is lifted up and over the mountain, cooling as it rises. If the air cools to its saturation point, the water vapor condenses and a cloud forms), and pileus cloud ( is a smooth cloud found attached to either a mountain top or growing cumulus tower).

Clouds form when water vapor (water that has evaporated from the surface of the Earth) condenses (turns into liquid water or solid ice) onto microscopic dust particles (or other tiny particles) floating in the air. This condensation (cloud formation) happens when warm and cold air meet, when warm air rises up the side of a mountain and cools as it rises, and when warm air flows over a colder area, like a cool body of water. This occurs because cool air can hold less water vapor than warm air, and excess water condenses into either liquid or ice.

Water vapor and particles in the air such as dust or sea spray. If the air is saturated with water, the water vapor can condense into droplets or be deposited as ice crystals around the particles. A collection of billions of these tiny droplets or ice crystals forms a cloud.

A mass of air can become saturated with water when it is uplifted and cooled. Air is uplifted by a number of different processes, including orographic ascent, convection, and convergence. Orographic ascent takes place when the shape of the landscape forces air upward; convection occurs when air at ground level is heated by Earth's surface, becomes less dense, and then rises up through the cooler, denser air above it; and convergence happens when two air masses meet, forcing one of them upward. While most clouds are produced by uplift, some clouds are formed when water vapor is added to the air, for example, due to exhaust from an airplane.

Clouds continuously shift and change shape because of air movement. They dissipate as the water droplets evaporate or move apart from each other. Winds also carry clouds across the sky. Because different levels of the atmosphere have different winds, it is possible to see clouds that are at different levels moving at different speeds.

If you watch clouds over a period of time, you will likely see them forming, moving, and changing shape. These clouds can float because they are warmer that their surrounding environment.

How to protect yourself:

Before you ever subject yourself to a possible dangerous and unnecessary CT scan, consult your doctor. Recognize that scans often produce false positives, signaling problems where none exists. If your physician suggests you need a test involving radiation, ask about alternatives such as echocardiography (using high-frequency sound) or magnetic resonance imaging (MRI, using strong magnetic fields). Neither subjects you to radiation. But neither is advanced enough to rival the power of X-rays to give your doctors a clear view inside your small vessels.

RADIATION YOU WILL RECEIVE FROM CARDIAC TESTS 

The annual "background radiation" dose from cosmic rays and radioactive elements in the earth is effectively about the same (about 10 mSv) dose as what you get from one trip to a catheterization lab for invasive angiography. Catheterization lab tests use X-rays of a portion of the heart to reveal blockages in small arteries.

CT (computed tomography) angiography is non-invasive but exposes you to as much as twice the radiation you receive from invasive angiography. Computers create CT scan images from X-ray data.

Industrial Use:

nondestructive inspection (NDI), is testing that does not destroy the test object. NDE is vital for constructing and maintaining all types of components and structures. To detect different defects such as cracking and corrosion, there are different methods of testing available, such as X-ray (where cracks show up on the film) and ultrasound (where cracks show up as an echo blip on the screen). This article is aimed mainly at industrial NDT, but many of the methods described here can be used to test the human body. In fact methods from the medical field have often been adapted for industrial use, as was the case with Phased array ultrasonics and Computed radiography.

While destructive testing usually provides a more reliable assessment of the state of the test object, destruction of the test object usually makes this type of test more costly to the test object's owner than nondestructive testing. Destructive testing is also inappropriate in many circumstances, such as forensic investigation. That there is a tradeoff between the cost of the test and its reliability favors a strategy in which most test objects are inspected nondestructively; destructive testing is performed on a sampling of test objects that is drawn randomly for the purpose of characterizing the testing reliability of the nondestructive test.

Industrial Needs:

It is very difficult to weld or mold a solid object that has the risk of breaking in service, so testing at manufacture and during use is often essential. During the process of casting a metal object, for example, the metal may shrink as it cools, and crack or introduce voids inside the structure. Even the best welders (and welding machines) do not make 100% perfect welds. Some typical weld defects that need to be found and repaired are lack of fusion of the weld to the metal and porous bubbles inside the weld, both of which could cause a structure to break or a pipeline to rupture.

During their service lives, many industrial components need regular nondestructive tests to detect damage that may be difficult or expensive to find by everyday methods. For example:

• aircraft skins need regular checking to detect cracks;
• underground pipelines are subject to corrosion and stress corrosion cracking;
• pipes in industrial plants may be subject to erosion and corrosion from the products they carry;
• concrete structures may be weakened if the inner reinforcing steel is corroded;
• pressure vessels may develop cracks in welds;
• the wire ropes in suspension bridges are subject to weather, vibration, and high loads, so testing for broken wires and other damage is important.

Over the past centuries, swordsmiths, blacksmiths, and bell-makers would listen to the ring of the objects they were creating to get an indication of the soundness of the material. The wheel-tapper would test the wheels of locomotives for the presence of cracks, often caused by fatigue — a function that is now carried out by instrumentation and referred to as the acoustic impact technique.

DNA is the hereditary material in humans and almost all other organisms. Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA).

The information in DNA is stored as a code made up of four chemical bases:

Human DNA consists of about 3 billion bases, and more than 99 percent of those bases are the same in all people. The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences.

Liquefaction occurs when the strength and stiffness of a soil is reduced by earthquake shaking or other rapid loading. *Liquefaction and related phenomena have been responsible for tremendous amounts of damage in historical earthquakes around the world. Liquefaction occurs in saturated soils, that is, soils in which the space between individual particles is completely filled with water. This water exerts a pressure on the soil particles that influences how tightly the particles themselves are pressed together. Prior to an earthquake, the water pressure is relatively low. However, earthquake shaking can cause the water pressure to increase to the point where the soil particles can readily move with respect to each other. which happens when loosely packed, water-logged sediments lose their strength in response to strong shaking, causes major damage during earthquakes.

Typical effects of liquefaction include:

Loss of bearing strength –the ground can liquefy and lose its ability to support structures.

Lateral spreading - the ground can slide down very gentle slopes or toward stream banks riding on a buried liquefied layer.

Quicksand is not a unique type of soil; it is usually just sand or another type of grainy soil. Quicksand is nothing more than a soupy mixture of sand and water. It can occur anywhere under the right conditions.

Quicksand is created when water saturates an area of loose sand and the ordinary sand is agitated. When the water trapped in the batch of sand can't escape, it creates liquefied soil that can no longer support weight. There are two ways in which sand can become agitated enough to create quicksand:

The vibration plus the water barrier reduces the friction between the sand particles and causes the sand to behave like a liquid. To understand quicksand, you have to understand the process of liquefaction. When soil liquefies, as with quicksand, it loses strength and behaves like a viscous liquid rather than a solid. Liquefaction can cause buildings to sink significantly during earthquakes.

While quicksand can occur in almost any location where water is present, there are certain locations where it's more prevalent. Places where quicksand is most likely to occur include: On beaches, Lakes shorelines, Marshes, Riverbanks and near springs.

Quicksand has a density of about 125 pounds per cubic foot, which means you can float more easily on quicksand than on water. The key is to not panic. Most people who drown in quicksand are usually those who panic and begin flailing their arms and legs.

It may be possible to drown in quicksand if you were to fall in over your head and couldn't get your head back above the surface, although it's rare for quicksand to be that deep. Most likely, if you fall in, you will float to the surface. However, the sand-to-water ratio of quicksand can vary, causing some quicksand to be less buoyant. When you try pulling your leg out of quicksand or mud for that matter, you are working against a vacuum left behind by the movement, 

The best thing to do is to make slow movements and bring yourself to the surface, then just lie on your back,  paddle slowly with your arms stretched out wide,  and if possible heading  for the edge.

The hazard from landslides can be reduced by avoiding construction on steep slopes and existing landslides, or by stabilizing the slopes. Stability increases when ground water is prevented from rising in the landslide mass by;covering the landslide with an impermeable membrane, directing surface water away from the landslide, draining ground water away from the landslide, and minimizing surface irrigation. Slope stability is also increased when a retaining structure and/or the weight of a soil/rock berm are placed at the toe of the landslide or when mass is removed from the top of the slope.

• Springs, seeps, or saturated ground in areas that have not typically been wet before.
• New cracks or unusual bulges in the ground, street pavements or sidewalks.
• Soil moving away from foundations.
• Ancillary structures such as decks and patios tilting and/or moving relative to the main house.
• Tilting or cracking of concrete floors and foundations.
• Broken water lines and other underground utilities.
• Leaning telephone poles, trees, retaining walls or fences.
• Offset fence lines.
• Sunken or down-dropped road beds.
• Rapid increase in creek water levels, possibly accompanied by increased turbidity (soil content).
• Sudden decrease in creek water levels though rain is still falling or just recently stopped.
• Sticking doors and windows, and visible open spaces indicating jambs and frames out of plumb.
• A faint rumbling sound that increases in volume is noticeable as the landslide nears.
• Unusual sounds, such as trees cracking or boulders knocking together, might indicate moving debris.

As a result of the quakes, large areas sank into the earth, new lakes were formed (notably Reelfoot Lake, Tennessee), and the Mississippi River changed its course, creating numerous geographic exclaves, including Kentucky Bend, along the state boundaries which are defined by the river.

The Southern Oscillation Index is the difference in surface pressure between Tahiti, French Polynesia and Darwin, Australia is a measure of the strength of the trade winds, which have a component of flow from regions of high to low pressure. High SOI (large pressure difference) is associated with stronger than normal trade winds and La Niña conditions, and low SOI (smaller pressure difference) is associated with weaker than normal trade winds and El Niño conditions. 

El Niño denotes a warm southward flowing ocean current that occures every year around late December off the west coast of Peru and Ecuador. The term was later restricted to unusually strong warmings that disrupted local fish and bird populations every few years. However, as a result of the frequent association of South American coastal temperature anomalies with interannual basin scale equatorial warm events, El Niño has also become synonymous with larger scale, climatically significant, warm events. There is not, however, unanimity in the use of the term El Niño.

La Niña, is defined as colder than normal sea-surface temperatures in the central and eastern tropical Pacific ocean that impact global weather patterns. La Niña conditions recur every few years and can persist for as long as two years. La Niña is preceded by a buildup of cooler-than-normal subsurface waters in the tropical Pacific. Eastward-moving atmospheric and oceanic waves help bring the cold water to the surface through a complex series of events still being studied. In time, the easterly trade winds strengthen, cold upwelling off Peru and Ecuador intensifies, Sea-surface temperatures along the equator can fall as much as 7 degrees F below normal.

Ellipticals

Lenticulars

They possess both a bulge and a disk, but lack spiral arms. There is little or no gas and so all the stars are old. They appear to be an intermediate.

*Spirals

Fall into several classes depending on their shape and the relative size of the bulge. Spiral galaxies are characterized by the presence of gas in the disk which means star formation remains active at the present time, hence the younger population of stars. Spirals are divided into ordinary and barred spirals; in barred systems the spiral arms arise from a straight ``bar" passing through the center, while ordinary spirals have a more S-shaped inner configuration. Ordinary spiral are denoted S and barred systems SB. Both usually contain a central bulge, often sharing many properties with elliptical galaxies, surrounded by a thin rotating disk containing whatever spiral structure there may be. Spirals are subdivided into a sequence jointly defined by the winding and prominence of the spiral arms, and the relative importance of the central bulge. Spirals are usually found in the low density galactic field where their delicate shape can avoid disruption by tidal forces from neighbouring galaxies.

'A'a: Hawaiian word used to describe a lava flow whose surface is broken into rough angular fragments. Click here to view a photo of 'a'a.

Accessory: A mineral whose presence in a rock is not essential to the proper classification of the rock.

Accidental: Pyroclastic rocks that are formed from fragments of non-volcanic rocks or from volcanic rocks not related to the erupting volcano.

Accretionary Lava Ball: A rounded mass, ranging in diameter from a few centimeters to several meters, [carried] on the surface of a lava flow (e.g., 'a'a) or on cinder-cone slopes [and formed] by the molding of viscous lava around a core of already solidified lava.

Acid: A descriptive term applied to igneous rocks with more than 60% silica (SiO2).

Active Volcano: A volcano that is erupting. Also, a volcano that is not presently erupting, but that has erupted within historical time and is considered likely to do so in the future.

Agate: A variety of quartz distinguished by its extremely fine grain size and bright colors. Agates may occur in almost any kind of rock, but are especially common in volcanics.

Agglutinate: A pyroclastic deposit consisting of an accumulation of originally plastic ejecta and formed by the coherence of the fragments upon solidification.

Alkalic: Rocks which contain above average amounts of sodium and/or potassium for the group of rocks for which it belongs. For example, the basalts of the capping stage of Hawaiian volcanoes are alkalic. They contain more sodium and/or potassium than the shield-building basalts that make the bulk of the volcano.

Andesite: Volcanic rock (or lava) characteristically medium dark in color and containing 54 to 62 percent silica and moderate amounts of iron and magnesium.

Ash: Fine particles of pulverized rock blown from an explosion vent. Measuring less than 1/10 inch in diameter, ash may be either solid or molten when first erupted. By far the most common variety is vitric ash (glassy particles formed by gas bubbles bursting through liquid magma).

Ashfall (Airfall): Volcanic ash that has fallen through the air from an eruption cloud. A deposit so formed is usually well sorted and layered.

Ash Flow: A turbulent mixture of gas and rock fragments, most of which are ash-sized particles, ejected violently from a crater or fissure. The mass of pyroclastics is normally of very high temperature and moves rapidly down the slopes or even along a level surface.

Asthenosphere: The shell within the earth, some tens of kilometers below the surface and of undefined thickness, which is a shell of weakness where plastic movements take place to permit pressure adjustments.

Aquifer: A body of rock that contains significant quantities of water that can be tapped by wells or springs.

Avalanche: A large mass of material or mixtures of material falling or sliding rapidly under the force of gravity. Avalanches often are classified by their content, such as snow, ice, soil, or rock avalanches. A mixture of these materials is a debris avalanche.

Basalt:  The commonest volcanic rock. Basalt is very fine grained, has a smooth texture, and is quite black if fresh.  Weathered or altered basalt may be greenish black or various rusty shades of brown, occasionally even brick red. Many specimens are full of gas bubbles. Contains 45% to 54% silica, and generally is rich in iron and magnesium.

Basement: The undifferentiated rocks that underlie the rocks of interest in an area.

Basic: A descriptive term applied to igneous rocks (basalt and gabbro) with silica (SiO2) between 44% and 52%.

Bauxite: A type of laterite soil that is very rich in aluminum and poor in iron. The best bauxites are nearly white.

Bench: The unstable, newly-formed front of a lava delta.

Blister: A swelling of the crust of a lava flow formed by the puffing-up of gas or vapor beneath the flow. Blisters are about 1 meter in diameter and hollow.

Block: Angular chunk of solid rock ejected during an eruption.

Bomb: Fragment of molten or semi-molten rock, 2 1/2 inches to many feet in diameter, which is blown out during an eruption. Because of their plastic condition, bombs are often modified in shape during their flight or upon impact.

Caldera: A basin-shaped volcanic depression; by definition, at least a mile in diameter. Such large depressions are typically formed by the subsidence of volcanoes. Crater Lake occupies the best-known caldera in the Cascades.

Capping Stage: Refers to a stage in the evolution of a typical Hawaiian volcano during which alkalic, basalt, and related rocks build a steeply, sloping cap on the main shield of the volcano. Eruptions are less frequent, but more explosive. The summit caldera may be buried.

Central Vent: A central vent is an opening at the Earth's surface of a volcanic conduit of cylindrical or pipe-like form.

Central Volcano: A volcano constructed by the ejection of debris and lava flows from a central point, forming a more or less symmetrical volcano.

Chromite: A mineral composed of chromium oxide. It is heavy and black and the only mineral source of chromium. Chromite always occurs in peridotite or serpentinite.

Cinder Cone: A volcanic cone built entirely of loose fragmented material (pyroclastics.)

Cirque: A steep-walled horseshoe-shaped recess high on a mountain that is formed by glacial erosion.

Cleavage: The breaking of a mineral along crystallographic planes, that reflects a crystal structure.

Composite Volcano: A steep volcanic cone built by both lava flows and pyroclastic eruptions.

Compound Volcano: A volcano that consists of a complex of two or more vents, or a volcano that has an associated volcanic dome, either in its crater or on its flanks. Examples are Vesuvius and Mont Pelee.

Compression Waves: Earthquake waves that move like a slinky. As the wave moves to the left, for example, it expands and compresses in the same direction as it moves. Usage of compression waves.

Conduit: A passage followed by magma in a volcano.

Continental Crust: Solid, outer layers of the earth, including the rocks of the continents. Usage of continental crust.

Continental Drift: The theory that horizontal movement of the earth's surface causes slow, relative movements of the continents toward or away from one another.

Country Rocks: The rock intruded by and surrounding an igneous intrusion.

Crater: A steep-sided, usually circular depression formed by either explosion or collapse at a volcanic vent.

Craton: A part of the earth's crust that has attained stability and has been little deformed for a prolonged period.

Cretaceous: The interval of time between 135  and 70 million years before the present.

Crust: The rigit outer part of the earth extending down to a depth of about 60 miles.

Curtain of Fire: A row of coalescing lava fountains along a fissure; a typical feature of a Hawaiian-type eruption.

Dacite: Volcanic rock (or lava) that characteristically is light in color and contains 62% to 69% silica and moderate a mounts of sodium and potassium.

Debris Avalanche: A rapid and unusually sudden sliding or flowage of unsorted masses of rock and other material. As applied to the major avalanche involved in the eruption of Mount St. Helens, a rapid mass movement that included fragmented cold and hot volcanic rock, water, snow, glacier ice, trees, and some hot pyroclastic material. Most of the May 18, 1980 deposits in the upper valley of the North Fork Toutle River and in the vicinity of Spirit Lake are from the debris avalanche.

Debris Flow: A mixture of water-saturated rock debris that flows downslope under the force of gravity (also called lahar or mudflow).

Detachment Plane: The surface along which a landslide disconnects from its original position.

Devonian: A period of time in the Paleozoic Era that covered the time span between 400 and 345 million years.

Diatreme: A breccia filled volcanic pipe that was formed by a gaseous explosion.

Dike: A sheetlike body of igneous rock that cuts across layering or contacts in the rock into which it intrudes.

Diorite: A coarsely granular rock composed of milky crystals of feldspar and abundant grains of black hornblende or mica. It some-what resembles granite except for being much darker and lacking quartz. Like granite, it forms when molten magma cools deep within the earth's crust.

Dome: A steep-sided mass of viscous (doughy) lava extruded from a volcanic vent (often circular in plane view) and spiny, rounded, or flat on top. Its surface is often rough and blocky as a result of fragmentation of the cooler, outer crust during growth of the dome.

Dormant Volcano: Literally, "sleeping." The term is used to describe a volcano which is presently inactive but which may erupt again. Most of the major Cascade volcanoes are believed to be dormant rather than extinct.

Drainage Basin: The area of land drained by a river system.

Echelon: Set of geologic features that are in an overlapping or a staggered arrangement (e.g., faults). Each is relatively short, but collectively they form a linear zone in which the strike of the individual features is oblique to that of the zone as a whole.

Ejecta: Material that is thrown out by a volcano, including pyroclastic material (tephra) and lava bombs.

Eocene: The period of time between about 60 and 40 million years before the present.

Episode: An episode is a volcanic event that is distinguished by its duration or style.

Eruption: The process by which solid, liquid, and gaseous materials are ejected into the earth's atmosphere and onto the earth's surface by volcanic activity. Eruptions range from the quiet overflow of liquid rock to the tremendously violent expulsion of pyroclastics.

Eruption Cloud: The column of gases, ash, and larger rock fragments rising from a crater or other vent. If it is of sufficient volume and velocity, this gaseous column may reach many miles into the stratosphere, where high winds will carry it long distances.

Eruptive Vent: The opening through which volcanic material is emitted.

Evacuate: Temporarily move people away from possible danger.

Extinct Volcano: A volcano that is not presently erupting and is not likely to do so for a very long time in the future. Usage of extinct.

Extrusion: The emission of magmatic material at the earth's surface. Also, the structure or form produced by the process (e.g., a lava flow, volcanic dome, or certain pyroclastic rocks).

Fault: A crack or fracture in the earth's surface. Movement along the fault can cause earthquakes or--in the process of mountain-building--can release underlying magma and permit it to rise to the surface.

Fault Scarp: A steep slope or cliff formed directly by movement along a fault and representing the exposed surface of the fault before modification by erosion and weathering.

Feldspar: An extremely common and abundant family of minerals most which of which are rather milky in appearance. In light-colored rocks the feldspars are commonly pink or white; in dark -colored rocks they are usually either greenish or white.

Fire fountain: See also: lava fountain

Fissures: Elongated fractures or cracks on the slopes of a volcano. Fissure eruptions typically produce liquid flows, but pyroclastics may also be ejected.

Flank Eruption: An eruption from the side of a volcano (in contrast to a summit eruption.)

Fluvial: Produced by the action of of flowing water.

Formation: A body of rock identified by lithic characteristics and stratigraphic position and is mappable at the earth's surface or traceable in the subsurface.

Fracture: The manner of breaking due to intense folding or faulting.

Fumarole: A vent or opening through which issue steam, hydrogen sulfide, or other gases. The craters of many dormant volcanoes contain active fumaroles.

Gabbro: A coarsely granular rock composed of greenish white feldspar and black pyroxene. It is usually very dark in color.

Geothermal Energy: Energy derived from the internal heat of the earth.

Geothermal Power: Power generated by using the heat energy of the earth.

Graben: An elongate crustal block that is relatively depressed (downdropped) between two fault systems.

Granite: A granular rock composed of crystals of glassy-looking quartz, milky feldspar, and black hornblende or biotite. It forms when andesite magma cools very slowly beneath the surface.

Greenstone: Volcanic rocks that have been recrystallized at high temperature and pressure (metamorphosed). Their bright green color is both startling and distinctive.

Guyot: A type of seamount that has a platform top. Named for a nineteenth-century Swiss-American geologist.

Hardness: The resistance of a mineral to scratching.

Harmonic Tremor: A continuous release of seismic energy typically associated with the underground movement of magma. It contrasts distinctly with the sudden release and rapid decrease of seismic energy associated with the more common type of earthquake caused by slippage along a fault.

Heat transfer: Movement of heat from one place to another.

Heterolithologic: Material is made up of a heterogeneous mix of different rock types. Instead of being composed on one rock type, it is composed of fragments of many different rocks.

Holocene: The time period from 10,000 years ago to the present. Also, the rocks and deposits of that age.

Horizontal Blast: An explosive eruption in which the resultant cloud of hot ash and other material moves laterally rather than upward.

Horst: A block of the earth's crust, generally long compared to its width, that has been uplifted along faults relative to the rocks on either side.

Hot Spot: A volcanic center, 60 to 120 miles (100 to 200 km) across and persistent for at least a few tens of million of years, that is thought to be the surface expression of a persistent rising plume of hot mantle material. Hot spots are not linked to arcs and may not be associated with ocean ridges.

Hot-spot Volcanoes: Volcanoes related to a persistent heat source in the mantle.

Hyaloclastite: A deposit formed by the flowing or intrusion of lava or magma into water, ice, or water-saturated sediment and its consequent granulation or shattering into small angular fragments.

Hydrothermal Reservoir: An underground zone of porous rock containing hot water.

Hypabyssal: A shallow intrusion of magma or the resulting solidified rock.

Hypocenter: The place on a buried fault where an earthquake occurs.

Igneous Rock: A rock formed by cooling of a molten magma either on the surface after it has erupted from a volcano or at depth within the crust of the earth.

Ignimbrite: The rock formed by the widespread deposition and consolidation of ash flows and Nuees Ardentes. The term was originally applied only to densely welded deposits but now includes non-welded deposits.

Intensity: A measure of the effects of an earthquake at a particular place. Intensity depends not only on the magnitude of the earthquake, but also on the distance from the epicenter and the local geology.

Intermediate: A descriptive term applied to igneous rocks that are transitional between basic and acidic with silica (SiO2) between 54% and 65%.

Intrusion: The process of emplacement of magma in pre-existing rock. Also, the term refers to igneous rock mass so formed within the surrounding rock.

Joint: A surface of fracture in a rock.

Jurassic: The geologic period that began about 180 million years before the present and ended about 135 million  years before the present.

Juvenile: Pyroclastic material derived directly from magma reaching the surface.

Kipuka: An area surrounded by a lava flow.

Laccolith: A body of igneous rocks with a flat bottom and domed top. It is parallel to the layers above and below it.

Lahar: A torrential flow of water-saturated volcanic debris down the slope of a volcano in response to gravity. A type of mudflow. Usage of lahar. For a larger discussion on lahars, click here.

Landsat: A series of unmanned satellites orbiting at about 706 km (438 miles) above the surface of the earth. The satellites carry cameras similar to video cameras and take images or pictures showing features as small as 30 m or 80 m wide, depending on which camera is used. Usage of Landsat.

Lapilli: Literally, "little stones." Round to angular rock fragments, measuring 1/10 inch to 2 1/2 inches in diameter, which may be ejected in either a solid or molten state.

Laterite: A type of red soil that develops under wet, tropical conditions. Most laterite soils are very deep and also very infertile.

Lava: Magma which has reached the surface through a volcanic eruption. The term is most commonly applied to streams of liquid rock that flow from a crater or fissure. It also refers to cooled and solidified rock.

Lava Dome: Mass of lava, created by many individual flows, that has built a dome-shaped pile of lava.

Lava Flow: An outpouring of lava onto the land surface from a vent or fissure. Also, a solidified tongue like or sheet-like body formed by outpouring lava.

Lava Fountain: A rhythmic vertical fountainlike eruption of lava.

Lava Lake (Pond): A lake of molten lava, usually basaltic, contained in a vent, crater, or broad depression of a shield volcano.

Lava Shields: A shield volcano made of basaltic lava.

Lava Tube: A tunnel formed when the surface of a lava flow cools and solidifies while the still-molten interior flows through and drains away.

Limu O Pele (Pele Seaweed): Delicate, translucent sheets of spatter filled with tiny glass bubbles.

Limestone: Limestone is a sedimentary rock composed of the mineral calcite (calcium carbonate). The primary source of this calcite is usually marine organisms. These organisms secrete shells that settle out of the water column and are deposited on ocean floors as pelagic ooze

Lithic: Of or pertaining to stone.

Lithosphere: The rigid crust and uppermost mantle of the earth. Thickness is on the order of 60 miles (100 km). Stronger than the underlying asthenosphere.

Luster: The reflection of light from the surface of a mineral.

Maar: A volcanic crater that is produced by an explosion in an area of low relief, is generally more or less circular, and often contains a lake, pond, or marsh.

Mafic: An igneous composed chiefly of one or more dark-colored minerals.

Magma: Molten rock beneath the surface of the earth.

Magma Chamber: The subterranean cavity containing the gas-rich liquid magma which feeds a volcano.

Magmatic: Pertaining to magma.

Magnitude: A numerical expression of the amount of energy released by an earthquake, determined by measuring earthquake waves on standardized recording instruments (seismographs.) The number scale for magnitudes is logarithmic rather than arithmetic. Therefore, deflections on a seismograph for a magnitude 5 earthquake, for example, are 10 times greater than those for a magnitude 4 earthquake, 100 times greater than for a magnitude 3 earthquake, and so on.

Mantle: The zone of the earth below the crust and above the core.

Marine Rocks: Rocks that formed in seawater.

Matrix: The solid matter in which a fossil or crystal is embedded. Also, a binding substance (e.g., cement in concrete).

Mesozoic: The era of geologic time comprising the Triassic, Jurassic and Cretaceous periods. Mesozoic time began about 225 million years before the present and ended about 70 million years before the present.

Metamorphism: The process of recrystallizing rocks under conditions of high temperature and pressure and converting them (Recrystallizing) into new kinds of rock.

Mica: A family of common minerals which may be either black or colorless but are always flaky. Especially abundant in granites and similar rocks.

Miocene: An epoch in Earth's history from about 24 to 5 million years ago. Also refers to the rocks that formed in that epoch.

Moho: Also called the Mohorovicic discontinuity. The surface or discontinuity that separates the crust from the mantle. The Moho is at a depth of 5-10 km beneath the ocean floor and about 35 km below the continents (but down to 60 km below mountains). Named for Andrija Mohorovicic, a Croatian seismologist.

Monogenetic: A volcano built by a single eruption.

Mudflow: A flowage of water-saturated earth material possessing a high degree of fluidity during movement. A less-saturated flowing mass is often called a debris flow. A mudflow originating on the flank of a volcano is properly called a lahar.

Mudstone: A sedimentary rock that started out as mud.

Nuees Ardentes: A French term applied to a highly heated mass of gas-charged ash which is expelled with explosive force and moves hurricane speed down the mountainside.

Obsidian: A black or dark-colored volcanic glass, usually composed of rhyolite.

Obligocene: The geologic period that started about 40 million years before the present and ended about 14 million years before the present.

Olivine: A pale green mineral which occurs in small crystals scattered through black ingneous rocks. Peridotite always contains olivine and so do some varieties of basalt and gabbro.

Oceanic Crust: The earth's crust where it underlies oceans.

Pali: Hawaiian word for steep hills or cliffs.

Pele Hair: A natural spun glass formed by blowing-out during quiet fountaining of fluid lava, cascading lava falls, or turbulent flows, sometimes in association with pele tears. A single strand, with a diameter of less than half a millimeter, may be as long as two meters.

Pele Tears: Small, solidified drops of volcanic glass behind which trail pendants of Pele hair. They may be tear-shaped, spherical, or nearly cylindrical.

Peralkaline: Igneous rocks in which the molecular proportion of aluminum oxide is less than that of sodium and potassium oxides combined.

Peridotite: A heavy,. black rock that forms most of the earth's interior. It is composed principally of black pyroxene and green olivine.

Perlite: A glassy form of rhyolite that contains some water. Most perlite is rather greenish but it comes in other colors. It puffs up like popcorn upon roasting to make lightweight chunks useful as a soil additive and in making special purpose concrete.

Phenocryst: A conspicuous, usually large, crystal embedded in porphyritic igneous rock.

Phreatic Eruption (Explosion): An explosive volcanic eruption caused when water and heated volcanic rocks interact to produce a violent expulsion of steam and pulverized rocks. Magma is not involved.

Phreatomagmatic: An explosive volcanic eruption that results from the interaction of surface or subsurface water and magma.

Pillow lava: Interconnected, sack-like bodies of lava formed underwater.

Pipe: A vertical conduit through the Earth's crust below a volcano, through which magmatic materials have passed. Commonly filled with volcanic breccia and fragments of older rock.

Pit Crater: A crater formed by sinking in of the surface, not primarily a vent for lava.

Plagioclase: A variety of feldspar which contains sodium and potasium.

Plastic: Capable of being molded into any form, which is retained.

Plates: One of the rigid slabs that make the outer crust of the earth. Plates are about 60 miles thick and most of them cover areas of many hundreds of square miles.

Plate Tectonics: The theory that the earth's crust is broken into about 10 fragments (plates,) which move in relation to one another, shifting continents, forming new ocean crust, and stimulating volcanic eruptions.

Pleistocene: A epoch in Earth history from about 2-5 million years to 10,000 years ago. Also refers to the rocks and sediment deposited in that epoch.

Plinian Eruption: An explosive eruption in which a steady, turbulent stream of fragmented magma and magmatic gases is released at a high velocity from a vent. Large volumes of tephra and tall eruption columns are characteristic.

Plug: Solidified lava that fills the conduit of a volcano. It is usually more resistant to erosion than the material making up the surrounding cone, and may remain standing as a solitary pinnacle when the rest of the original structure has eroded away.

Plug Dome: The steep-sided, rounded mound formed when viscous lava wells up into a crater and is too stiff to flow away. It piles up as a dome-shaped mass, often completely filling the vent from which it emerged.

Pluton: A large igneous intrusion formed at great depth in the crust.

Polygenetic: Originating in various ways or from various sources.

Precambrian:All geologic time from the beginning of Earth history to 570 million years ago. Also refers to the rocks that formed in that epoch.

Pumice: Light-colored, frothy volcanic rock, usually of dacite or rhyolite composition, formed by the expansion of gas in erupting lava. Commonly seen as lumps or fragments of pea-size and larger, but can also occur abundantly as ash-sized particles. Usage of pumice.

Pyroclastic: Pertaining to fragmented (clastic) rock material formed by a volcanic explosion or ejection from a volcanic vent.

Pyroclastic Flow: Lateral flowage of a turbulent mixture of hot gases and unsorted pyroclastic material (volcanic fragments, crystals, ash, pumice, and glass shards) that can move at high speed (50 to 100 miles an hour.) The term also can refer to the deposit so formed.

Quartz: The commonest of all minerals. It comes in a variety of colors and disguises, but usually occurs in clear, glassy grains. Quartz is the mineral form of silica.

Quaternary: The period of Earth's history from about 2 million years ago to the present; also, the rocks and deposits of that age.

Radiocarbon Dating: A method of determining the age of specimens of organic material by analysing their content of carbon-14 which is weakly radioactive. The method only works on objects less than about 40,000 years old, so geologist rarely use it.

Relief: The vertical difference between the summit of a mountain and the adjacent valley or plain.

Renewed Volcanism State: Refers to a state in the evolution of a typical Hawaiian volcano during which --after a long period of quiescence--lava and tephra erupt intermittently. Erosion and reef building continue.

Repose: The interval of time between volcanic eruptions.

Rhyodacite: An extrusive rock intermediate in composition between dacite and rhyolite.

Rhyolite: Volcanic rock (or lava) that characteristically is light in color, contains 69% silica or more, and is rich in potassium and sodium.

Ridge, Oceanic: A major submarine mountain range.

Rift System: The oceanic ridges formed where tectonic plates are separating and a new crust is being created; also, their on-land counterparts such as the East African Rift.

Rift Zone: A zone of volcanic features associated with underlying dikes. The location of the rift is marked by cracks, faults, and vents.

Ring of Fire: The regions of mountain-building earthquakes and volcanoes which surround the Pacific Ocean.

Sandstone: A common sedimentary rock that was originally sand.

Scoria: A bomb-size (> 64 mm) pyroclast that is irregular in form and generally very vesicular. It is usually heavier, darker, and more crystalline than pumice.

Seafloor Spreading: The mechanism by which new seafloor crust is created at oceanic ridges and slowly spreads away as plates are separating.

Seamount: A submarine volcano.

Seismograph: An instrument that records seismic waves; that is, vibrations of the earth.

Seismologist: Scientists who study earthquake waves and what they tell us about the inside of the Earth. Usage of seismologist.

Seismometer: An instrument that measures motion of the ground caused by earthquake waves.

Serpentinite: A dark, greenish rock that is usually fairly soft and rather greasy looking. Many specimens feel soapy because they contain some talc. Serpentinite forms by the reaction of peridotite with water. It forms an important part of the oceanic crust.

Shearing: The motion of surfaces sliding past one another.

Shear Waves: Earthquake waves that move up and down as the wave itself moves. For example, to the left. Usage of shear waves.

Shield Volcano: A gently sloping volcano (very low profile) in the shape of a flattened dome and built almost exclusively of lava flows.

Shoshonite: A trachyandesite composed of olivine and augite phenocrysts in a groundmass of labradorite with alkali feldspar rims, olivine, augite, a small amount of leucite, and some dark-colored glass. Its name is derived from the Shoshone River, Wyoming and given by Iddings in 1895.

Silica: A chemical combination of silicon and oxygen.

Sill: A tabular body of intrusive igneous rock, parallel to the layering of the rocks into which it intrudes.

Skylight: An opening formed by a collapse in the roof of a lava tube.

Solfatara: A type of fumarole, the gases of which are characteristically sulfurous.

Spatter Cone: A low, steep-sided cone of spatter built up on a fissure or vent. It is usually of basaltic material.

Spatter Rampart: A ridge of congealed pyroclastic material (usually basaltic) built up on a fissure or vent.

Specific Gravity: The density of a mineral divided by the density of water.

Spines: Horn-like projections formed upon a lava dome.

Stalactite: A cone shaped deposit of minerals hanging from the roof of a cavern.

Stratigraphic: The study of rock strata, especially of their distribution, deposition, and age.

Stratovolcano: A volcano composed of both lava flows and pyroclastic material.

Streak: The color of a mineral in the powdered form.

Strike-Slip Fault: A nearly vertical fault with side-slipping displacement.

Strombolian Eruption: A type of volcanic eruption characterized by jetting of clots or fountains of fluid basaltic lava from a central crater.

Subduction Zone: The zone of convergence of two tectonic plates, one of which usually overrides the other.

Surge: A ring-shaped cloud of gas and suspended solid debris that moves radially outward at high velocity as a density flow from the base of a vertical eruption column accompanying a volcanic eruption or crater formation.

Talus: A slope formed a the base of a steeper slope, made of fallen and disintegrated materials.

Tephra: Materials of all types and sizes that are erupted from a crater or volcanic vent and deposited from the air.

Tephrochronology: The collection, preparation, petrographic description, and approximate dating of tephra.

Tertiary: The period between the end of the Cretaceous and the end of the Pliocene time. The Teritiary period begain about 70 million years before the present and ended about 3 million year before the present.

Tilt: The angle between the slope of a part of a volcano and some reference. The reference may be the slope of the volcano at some previous time.

Trachyandesite: An extrusive rock intermediate in composition between trachyte and andesite.

Trachybasalt: An extrusive rock intermediate in composition between trachyte and basalt.

Trachyte: A group of fine-grained, generally porphyritic, extrusive igneous rocks having alkali feldspar and minor mafic minerals as the main components, and possibly a small amount of sodic plagioclase.

Tremor: Low amplitude, continuous earthquake activity often associated with magma movement.

Triassic: The period of geologic time that began about 225 years before the present and ended about 180 million years before the present.

Tsunami: A great sea wave produced by a submarine earthquake, volcanic eruption, or large landslide.

Tuff: Rock formed of pyroclastic material.

Tuff Cone: A type of volcanic cone formed by the interaction of basaltic magma and water. Smaller and steeper than a tuff ring.

Tuff Ring: A wide, low-rimmed, well-bedded accumulation of hyalo-clastic debris built around a volcanic vent located in a lake, coastal zone, marsh, or area of abundant ground water.

Tumulus: A doming or small mound on the crest of a lava flow caused by pressure due to the difference in the rate of flow between the cooler crust and the more fluid lava below.

Ultramafic: Igneous rocks made mostly of the mafic minerals hypersthene, augite, and/or olivine.

Unconformity: A substantial break or gap in the geologic record where a rock unit is overlain by another that is not next in stratigraphic sucession, such as an interruption in continuity of a depositional sequence of sedimentary rocks or a break between eroded igneous rocks and younger sedimentary strata. It results from a change that caused deposition to cease for a considerable time, and it normally implies uplift and erosion with loss of the previous formed record.

Vent: The opening at the earth's surface through which volcanic materials issue forth. 

Vesicle: A small air pocket or cavity formed in volcanic rock during solidification.

Viscosity: A measure of resistance to flow in a liquid (water has low viscosity while honey has a higher viscosity.)

Volcano: A vent in the surface of the Earth through which magma and associated gases and ash erupt; also, the form or structure (usually conical) that is produced by the ejected material.

Volcanic Arc: A generally curved linear belt of volcanoes above a subduction zone, and the volcanic and plutonic rocks formed there.

Volcanic Complex: A persistent volcanic vent area that has built a complex combination of volcanic landforms.

Volcanic Cone: A mound of loose material that was ejected ballistically.

Volcanic Neck: A massive pillar of rock more resistant to erosion than the lavas and pyroclastic rocks of a volcanic cone.

Vulcanian: A type of eruption consisting of the explosive ejection of incandescent fragments of new viscous lava, usually on the form of blocks. ("Vulcan" was the Roman god of fire)

Weathering: The complex of processes that combine to decompose solid rock into soil.

Water Table: The surface between where the pore space in rock is filled with water and where the the pore space in rock is filled with air.

1. Uranium fuel enriched to 3% in U-235 surrounded by water moderator; this is the option used in all U.S. power reactors.  (Used for the production of Electricty)
   
2. Natural (or slightly enriched) uranium surrounded by graphite moderator; this is the option used in Chernobyl-type reactors, which is known as a "Unstable Reactor". (Used for the production of Plutonium for nuclear bombs and Electricity)

The Earth will become a global desert, carbon dioxide levels will drop and there would not be enough carbon dioxide to support photosynthesis, and most plants would die.

The global wind pattern is also known as the "general circulation" and the surface winds of each hemisphere are divided into three wind belts:

-Polar Easterlies = from 60-90 degrees latitude.
-Prevailing  Westerlies = from 30-60 degrees latitude.
-Tropical (known as Trade winds) Easterlies = from 0-30 degrees latitudes.

"Super-typhoon" is a term utilized by the U.S. Joint Typhoon Warning Center for typhoons that reach maximum sustained 1-minute surface winds of at least 65 m/s (130 kt, 150 mph). This is the equivalent of a strong Saffir-Simpson category 4 or category 5 hurricane in the Atlantic basin or a category 5 severe tropical cyclone in the Australian basin.

"Major hurricane/Intense hurricane" is a term utilized by the National Hurricane Center for hurricanes that reach maximum sustained 1-minute surface winds of at least 50 m/s (96 kt, 111 mph). This is the equivalent of category 3, 4 and 5 on the Saffir-Simpson scale.

Hurricanes rotate in a counterclockwise direction around an "eye." A tropical storm becomes a hurricane when winds reach 74 mph. There are on average six Atlantic hurricanes each year; over a three-year period, approximately five hurricanes strike the United States coastline from Texas to Maine. The Atlantic hurricane season begins June 1 and ends November 30. The East Pacific hurricane season runs from May 15 through November 30, with peak activity occurring during July through September.

When hurricanes move onto land, the heavy rain, strong winds and heavy waves can damage buildings, trees and cars. The heavy waves are called a storm surge. Storm surge is very dangerous and a major reason why you MUST stay away from the ocean during a hurricane.

Scientists often use more specific terms than lahar when referring to moving masses of water and rock debris

Dense flows that consist of a relatively high percentage of coarse rock particles are debris flows. The size of sediment transported by debris flows ranges in size from clay and silt (less than 0.06 mm) to boulders as large as 10 m in diameter. A typical debris flow consists of about 2 parts sediment for every one part water. Thus, debris flows may consist of more than 80 percent sediment by weight!

Mudflow:

A debris flow composed of relatively small rock particles, dominantly sand and silt-sized particles (less than 2 mm in diameter), is often called a mudflow. Even though mudflows can transport large boulders and can have sediment concentrations as great as debris flows, their sediment composition typically consists of at least 50 percent sand, silt, and clay-size particles ("mud" refers to silt- and clay-size particles). Mudflow is probably the most familiar and commonly used term by nonscientists to describe dense mixtures of flowing sediment and water.

Hyperconcentrated Streamflow:

A flow containing between 40 and 80 percent sediment by weight is often referred to as hyperconcentrated streamflow. Debris flows and mudflows represent the most dense and concentrated mixtures of flowing sediment and water; they commonly are composed of more than 80 percent sediment by weight. Normal streamflow, which may contain as much as 40 percent sediment by weight, is the least dense and concentrated mixture of flowing sediment and water. Hyperconcentrated flows are finer grained than debris flows and mudflows, usually consisting of predominantly of sand-size particles. As a debris flow or mudflow moves down a river valley, they will eventually become more dilute by mixing with water in the river and by losing some of the sediment. When the percentage of sediment by weight drops below 80 percent, the flow transforms into hyperconcentrate streamflow.

Cohesive Lahars:

Debris flows or mudflows that contain more than 3 to 5 percent of clay-size sediment are sometimes referred to as cohesive lahars. Scientists may sometimes conclude that a relatively high concentration of clay in these flows indicates it began as a large landslide from the flank of a volcano. The interior parts of many volcanoes have been hydrothermally altered and consist of many clay particles.

Non-cohesive Lahars"

Debris flows or mudflows that contain less than 3 to 5 percent of clay-size sediment are sometimes referred to as non-cohesive lahars. Such a relatively low proportion of clay in this volcanic debris is considered by some scientists to be evidence that the lahar did not originate as a volcanic landslide, but rather in another way. For example, by the mixing of water melted from snow and ice with volcanic debris.

As a lahar rushes downstream from a volcano, its size, speed, and the amount of water and rock debris it carries constantly change. The beginning surge of water and rock debris often erodes rocks and vegetation from the side of a volcano and along the river valley it enters. This initial flow can also incorporate water from melting snow and ice (if present) and the river it overruns. By eroding rock debris and incorporating additional water, lahars can easily grow to more than 10 times their initial size. But as a lahar moves farther away from a volcano, it will eventually begin to lose its heavy load of sediment and decrease in size.

Lahars racing down river valleys and spreading across flood plains tens of kilometers downstream from a volcano often cause serious economic and environmental damage. The direct impact of a lahar's turbulent flow front or from the boulders and logs carried by the lahar can easily crush, abrade, or shear off at ground level just about anything in the path of a lahar. Even if not crushed or carried away by the force of a lahar, buildings and valuable land may become partially or completely buried by one or more cement-like layers of rock debris. By destroying bridges and key roads, lahars can also trap people in areas vulnerable to other hazardous volcanic activity, especially if the lahars leave deposits that are too deep, too soft, or too hot to cross.

After a volcanic eruption, the erosion of new loose volcanic deposits in the headwaters of rivers can lead to severe flooding and extremely high rates of sedimentation in areas far downstream from a volcano. Over a period of weeks to years, post-eruption lahars and high-sediment discharges triggered by intense rainfall frequently deposit rock debris that can bury entire towns and valuable agricultural land. Such lahar deposits may also block tributary stream valleys. As the area behind the blockage fills with water, areas upstream become inundated. If the lake is large enough and it eventually overtops or breaks through the lahar blockage, a sudden flood or a lahar may bury even more communities and valuable property downstream from the tributary.

The first working laser was built by Theodor Harold Maiman working at Hughes Research Laboratories in Malibu California, but the first patent was issued to Bell Laboratories in 1960.

Laser light is also characteristically monochromatic and coherent, which means all the photons produced are of the same wavelength and therefore color. Light emitted from a laser is usually emitted in a near parallel beam and the wavelength of the photons varies depending upon the type of laser and is not necessarily in the spectrum of visible light. The photons are traveling in the same direction and are in phase meaning the peaks and valleys of their electromagnetic waves coincide.

A laser basically consists of two main parts, an energy input and a gain medium. The energy input is called a pump source, the pump source could  be an electrical power supply, a chemical reaction or another laser. The power source inputs energy which is called laser pumping energy, this is what drives the process which produces the laser light.

The pumping energy is directed into the gain medium, this is the material which gives different lasers their individual characteristics. There are many different materials used as gain media including crystalline solids usually doped with transition metal ions or rare earth ions, gases such as CO₂ or He, semiconductors such as gallium arsenide and liquids dyes.

When energy is pumped into the gain medium it causes the particles in the medium to go into an excited state. Particle in this excited state may drop back to their ground state and when this happens they release their extra energy in the form of a photon of a specific wavelength. This photon may then collide with another particle, if this particle is in its ground state it will absorb the photon and become excited, if the particle is already excited the photon will cause it to drop to its ground state thus emitting another photon, this is called stimulated emission. Photons produced by stimulated emission are very similar to the initial photon in terms of wavelength, phase and polarization, this is what gives laser light its characteristics.

If energy continues to be put into the gain medium then it will reach a state where there are more of the particles are excited then in the ground state, this is called population inversion. This means that a photon passing through the medium has more chance of causing stimulated emission then of being absorbed, the laser is therefore acting as a light amplifier. Mirrors are placed at the front and back of the gain medium. The mirror at the back is fully reflective but the one at the front is only partially reflective. These mirrors will cause photons emitted to pass through the medium many times until they pass through the front mirror and are emitted in the laser beam. This will increase the chance of photons colliding with particles and continuing the chain reaction.

The maser which was the predecessor of the laser and emitted microwaves. Bell labs original worked with infrared frequencies but  later changed their focus to visible light and the optical maser which was how the laser was first referred to.

There are now many used for the used of lasers in Industry: such as in precise cutting of flat materials. Lasers have the advantage that there is no physical contact with the material so there is no chance of contamination, also there is less chance of the material warping as the laser energy can be focused on a very small area so the whole material is not heated.

In Astromony:

In the past Astronomers were used to working with images that are blurred by the Earth's atmosphere. However, a laser virtual star, launched from the W.M. Keck Observatory telescope, can be used to correct the atmosphere's distortions and clear up the picture. This new technology, called Laser Guide Star adaptive optics, will lead to important advances for the study of planets in our solar system and outside of our solar system, as well as galaxies, black holes, and how the universe formed.

Recent  computer  "snapshots" of the center of the Milky Way galaxy, targeting the supermassive black hole 26,000 light years away, at different wavelengths. This approach allowed researchers to study the infrared light emanating from very hot material just outside the black hole's "event horizon," about to be pulled through.

The research was conducted using the 10-meter Keck II Telescope, which is the world's first 10-meter telescope with a laser on it. Laser Guide Star allows astronomers to "generate an artificial bright star" exactly where they want it, which reveals the atmosphere's distortions.

Black holes are collapsed stars so dense that nothing can escape their gravitational pull, not even light. Black holes cannot be seen directly, but their influence on nearby stars is visible, and provides a signature, the supermassive black hole, with a mass more than 3 million times that of our sun, is in the constellation of Sagittarius. 

Lasers can measure enormous distances with great accuracy. A laser beam travels at a constant speed (the speed of light). The time it takes a laser beam to travel from its source, reflect off an object, and return to the source, will indicate the exact distance between the source and the object.

Motion is relative

All motion is relative to the observer or to some fixed object. When you see a car drive by, it is moving with respect to you. If you are in a car that is going at the same speed, the other car will not by moving with respect to you. But both cars are moving with respect to the ground. Using the Sun as an example, it is not moving across the sky (although it is traveling through the Milky Way galaxy) , the Planet Earth is. We consider motion with respect to the ground or the Earth. Within the Universe there is no real fixed point. The basis for Einstein's Theory of Relativity is that all motion is relative to what you define as a fixed point.

First Law of Motion: Law of Inertia

The relationship between an object's mass m, its acceleration a, and the applied force f is F=ma.
Acceleration and force are vectors (as indicated by their symbols being displayed in slant font); in
this law the direction of the force vector is the same as direction of the acceleration vector.

This is the most powerful of Newton's three Laws, because it allows quantitative calculations of dynamics: how do velocities change when forces are applied. Notice the fundamental difference between Newton's 2nd Law and the dynamics of Aristotle: according to Newton, a force causes only a change in velocity (an acceleration); it does not maintain the velocity as Aristotle held.

This is sometimes summarized by saying that under Newton, F = ma, but under Aristotle F = mv, where v is the velocity. Thus, according to Aristotle there is only a velocity if there is a force, but according to Newton an object with a certain velocity maintains that velocity unless a force acts on it to cause an acceleration.

Aristotle's view seems to be more in accord with common sense, but that is because of a failure to appreciate the role played by frictional forces. Once account is taken of all forces acting in a given situation it is the dynamics of Galileo and Newton, not of Aristotle, that are found to be in accord with the observations.

Third Law of Motion:

For Every action there is an equal and oppposite reaction.

-Measurement

In order to determine how fast an object is going, you measure the time it takes to cover a given distance, using the equation

d = vt

where:

• d is the distance
• v is the speed or velocity
• t is the time covered
• vt is v times t

From this equation, you can get the equation for velocity as v = d/t. Velocity (v) or speed equals the distance (d) traveled divided by the time (t) it takes to go that distance.

We distinguish between speed and velocity because if you add the speeds of objects, their directions are important. For example, the velocity of an airplane with respect to the ground would vary according to the direction of the wind.

-Acceleration is the increase of velocity over a period of time. Deceleration is the decrease of velocity. When you start running, you accelerate (increase your velocity) until you reach a constant speed.

Mathematically, acceleration is the change in velocity divided by the time for the change

a = (v₂ − v₁)/(t₂ − t₁)

where:

• v₂ − v₁ is the end velocity minus the beginning velocity
• t₂ − t₁ is the measured time period between the two velocities

Often this is written as a = Δv/Δt, where Δ is the Greek letter delta and stands for difference.

Multicellular animals must continually monitor and maintain a constant internal environment as well as monitor and respond to an external environment. In most, these two functions are coordinated by two integrated and coordinated organ systems: the nervous system and the endocrine system. 

Three basic functions are prformed by nervous systems:

1. Receive sensory input from internal and external environments
2. Integrate the input
3. Respond to stimuli

Sensory Input

Receptors are parts of the nervous system that sense changes in the internal or external environments. Sensory input can be in many forms, including pressure, taste, sound, light, blood pH, or hormone levels, that are converted to a signal and sent to the brain or spinal cord.

Integration and Output

In the sensory centers of the brain or in the spinal cord, the barrage of input is integrated and a response is generated. The response, a motor output, is a signal transmitted to organs than can convert the signal into some form of action, such as movement, changes in heart rate, release of hormones, etc.

Endocrine Systems

Some animals have a second control system, the endocrine system. The nervous system coordinates rapid responses to external stimuli. The endocrine system controls slower, longer lasting responses to internal stimuli. Activity of both systems is integrated.

Divisions of the Nervous System:

The nervous system monitors and controls almost every organ system through a series of positive and negative feedback loops.The Central Nervous System (CNS) includes the brain and spinal cord. The Peripheral Nervous System (PNS) connects the CNS to other parts of the body, and is composed of nerves (bundles of neurons).

Not all animals have highly specialized nervous systems. Those with simple systems tend to be either small and very mobile or large and immobile. Large, mobile animals have highly developed nervous systems: the evolution of nervous systems must have been an important adaptation in the evolution of body size and mobility.

Coelenterates, cnidarians, and echinoderms have their neurons organized into a nerve net. These creatures have radial symmetry and lack a head. Although lacking a brain or either nervous system (CNS or PNS) nerve nets are capable of some complex behavior.

Bilaterally symmetrical animals have a body plan that includes a defined head and a tail region. Development of bilateral symmetry is associated with cephalization, the development of a head with the accumulation of sensory organs at the front end of the organism. Flatworms have neurons associated into clusters known as ganglia, which in turn form a small brain. Vertebrates have a spinal cord in addition to a more developed brain.

Chordates have a dorsal rather than ventral nervous system. Several evolutionary trends occur in chordates: spinal cord, continuation of cephalization in the form of larger and more complex brains, and development of a more elaborate nervous system. The vertebrate nervous system is divided into a number of parts. The central nervous system includes the brain and spinal cord. The peripheral nervous system consists of all body nerves. Motor neuron pathways are of two types: somatic (skeletal) and autonomic (smooth muscle, cardiac muscle, and glands). The autonomic system is subdivided into the sympathetic and parasympathetic systems.

Neurons

Nervous tissue is composed of two main cell types: neurons and glial cells. Neurons transmit nerve messages. Glial cells are in direct contact with neurons and often surround them.

The neuron is the functional unit of the nervous system. Humans have about 100 billion neurons in their brain alone! While variable in size and shape, all neurons have three parts. Dendrites receive information from another cell and transmit the message to the cell body. The cell body contains the nucleus, mitochondria and other organelles typical of eukaryotic cells. The axon conducts messages away from the cell body.

Three types of neurons occur. Sensory neurons typically have a long dendrite and short axon, and carry messages from sensory receptors to the central nervous system. Motor neurons have a long axon and short dendrites and transmit messages from the central nervous system to the muscles (or to glands). Interneurons are found only in the central nervous system where they connect neuron to neuron.

Some axons are wrapped in a myelin sheath formed from the plasma membranes of specialized glial cells known as Schwann cells. Schwann cells serve as supportive, nutritive, and service facilities for neurons. The gap between Schwann cells is known as the node of Ranvier, and serves as points along the neuron for generating a signal. Signals jumping from node to node travel hundreds of times faster than signals traveling along the surface of the axon. This allows your brain to communicate with your toes in a few thousandths of a second.

The Nerve Message

The plasma membrane of neurons, like all other cells, has an unequal distribution of ions and electrical charges between the two sides of the membrane. The outside of the membrane has a positive charge, inside has a negative charge. This charge difference is a resting potential and is measured in millivolts. Passage of ions across the cell membrane passes the electrical charge along the cell. The voltage potential is -65mV (millivolts) of a cell at rest (resting potential). Resting potential results from differences between sodium and potassium positively charged ions and negatively charged ions in the cytoplasm. Sodium ions are more concentrated outside the membrane, while potassium ions are more concentrated inside the membrane. This imbalance is maintained by the active transport of ions to reset the membrane known as the sodium potassium pump. The sodium-potassium pump maintains this unequal concentration by actively transporting ions against their concentration gradients.

Changed polarity of the membrane, the action potential, results in propagation of the nerve impulse along the membrane. An action potential is a temporary reversal of the electrical potential along the membrane for a few milliseconds. Sodium gates and potassium gates open in the membrane to allow their respective ions to cross. Sodium and potassium ions reverse positions by passing through membrane protein channel gates that can be opened or closed to control ion passage. Sodium crosses first. At the height of the membrane potential reversal, potassium channels open to allow potassium ions to pass to the outside of the membrane. Potassium crosses second, resulting in changed ionic distributions, which must be reset by the continuously running sodium-potassium pump. Eventually enough potassium ions pass to the outside to restore the membrane charges to those of the original resting potential.The cell begins then to pump the ions back to their original sides of the membrane.

The action potential begins at one spot on the membrane, but spreads to adjacent areas of the membrane, propagating the message along the length of the cell membrane. After passage of the action potential, there is a brief period, the refractory period, during which the membrane cannot be stimulated. This prevents the message from being transmitted backward along the membrane.

Steps in an Action Potential

1. At rest the outside of the membrane is more positive than the inside.
2. Sodium moves inside the cell causing an action potential, the influx of positive sodium ions makes the inside of the membrane more positive than the outside.
3. Potassium ions flow out of the cell, restoring the resting potential net charges.
4. Sodium ions are pumped out of the cell and potassium ions are pumped into the cell, restoring the original distribution of ions.

Synapses

The junction between a nerve cell and another cell is called a synapse. Messages travel within the neuron as an electrical action potential. The space between two cells is known as the synaptic cleft. To cross the synaptic cleft requires the actions of neurotransmitters. Neurotransmitters are stored in small synaptic vessicles clustered at the tip of the axon.

Neurotransmitters tend to be small molecules, some are even hormones. The time for neurotransmitter action is between 0,5 and 1 millisecond. Neurotransmitters are either destroyed by specific enzymes in the synaptic cleft, diffuse out of the cleft, or are reabsorbed by the cell. More than 30 organic molecules are thought to act as neurotransmitters. The neurotransmitters cross the cleft, binding to receptor molecules on the next cell, prompting transmission of the message along that cell's membrane. Acetylcholine is an example of a neurotransmitter, as is norepinephrine, although each acts in different responses.

Diseases that affect the function of signal transmission can have serious consequences. Parkinson's disease has a deficiency of the neurotransmitter dopamine. Progressive death of brain cells increases this deficit, causing tremors, rigidity and unstable posture. L-dopa is a chemical related to dopamine that eases some of the symptoms (by acting as a substitute neurotransmitter) but cannot reverse the progression of the disease.

Peripheral Nervous System

The Peripheral Nervous System (PNS) contains only nerves and connects the brain and spinal cord (CNS) to the rest of the body. The axons and dendrites are surrounded by a white myelin sheath. Cell bodies are in the central nervous system (CNS) or ganglia. Ganglia are collections of nerve cell bodies. Cranial nerves in the PNS take impulses to and from the brain (CNS). Spinal nerves take impulses to and away from the spinal cord. There are two major subdivisions of the PNS motor pathways: the somatic and the autonomic.

Two main components of the PNS:

1. sensory (afferent) pathways that provide input from the body into the CNS.
2. motor (efferent) pathways that carry signals to muscles and glands (effectors).

Most sensory input carried in the PNS remains below the level of conscious awareness. Input that does reach the conscious level contributes to perception of our external environment.

Somatic Nervous System

The Somatic Nervous System (SNS) includes all nerves controlling the muscular system and external sensory receptors. External sense organs (including skin) are receptors. Muscle fibers and gland cells are effectors. The reflex arc is an automatic, involuntary reaction to a stimulus. When the doctor taps your knee with the rubber hammer, she/he is testing your reflex (or knee-jerk). The reaction to the stimulus is involuntary, with the CNS being informed but not consciously controlling the response. Examples of reflex arcs include balance, the blinking reflex, and the stretch reflex.

Sensory input from the PNS is processed by the CNS and responses are sent by the PNS from the CNS to the organs of the body.

Motor neurons of the somatic system are distinct from those of the autonomic system. Inhibitory signals, cannot be sent through the motor neurons of the somatic system.

Autonomic Nervous System

The Autonomic Nervous System is that part of PNS consisting of motor neurons that control internal organs. It has two subsystems. The autonomic system controls muscles in the heart, the smooth muscle in internal organs such as the intestine, bladder, and uterus. The Sympathetic Nervous System is involved in the fight or flight response. The Parasympathetic Nervous System is involved in relaxation. Each of these subsystems operates in the reverse of the other (antagonism). Both systems innervate the same organs and act in opposition to maintain homeostasis. For example: when you are scared the sympathetic system causes your heart to beat faster; the parasympathetic system reverses this effect.

Motor neurons in this system do not reach their targets directly (as do those in the somatic system) but rather connect to a secondary motor neuron which in turn innervates the target organ.

Central Nervous System

The Central Nervous System (CNS) is composed of the brain and spinal cord. The CNS is surrounded by bone-skull and vertebrae. Fluid and tissue also insulate the brain and spinal cord.

The brain is composed of three parts: the cerebrum (seat of consciousness), the cerebellum, and the medulla oblongata (these latter two are "part of the unconscious brain").

The medulla oblongata is closest to the spinal cord, and is involved with the regulation of heartbeat, breathing, vasoconstriction (blood pressure), and reflex centers for vomiting, coughing, sneezing, swallowing, and hiccuping. The hypothalamus regulates homeostasis. It has regulatory areas for thirst, hunger, body temperature, water balance, and blood pressure, and links the Nervous System to the Endocrine System. The midbrain and pons are also part of the unconscious brain. The thalamus serves as a central relay point for incoming nervous messages.

The cerebellum is the second largest part of the brain, after the cerebrum. It functions for muscle coordination and maintains normal muscle tone and posture. The cerebellum coordinates balance.

The conscious brain includes the cerebral hemispheres, which are are separated by the corpus callosum. In reptiles, birds, and mammals, the cerebrum coordinates sensory data and motor functions. The cerebrum governs intelligence and reasoning, learning and memory. While the cause of memory is not yet definitely known, studies on slugs indicate learning is accompanied by a synapse decrease. Within the cell, learning involves change in gene regulation and increased ability to secrete transmitters.

The Brain:

During embryonic development, the brain first forms as a tube, the anterior end of which enlarges into three hollow swellings that form the brain, and the posterior of which develops into the spinal cord. Some parts of the brain have changed little during vertebrate evolutionary history.

Vertebrate evolutionary trends include

1. Increase in brain size relative to body size.
2. Subdivision and increasing specialization of the forebrain, midbrain, and hindbrain.
3. Growth in relative size of the forebrain, especially the cerebrum, which is associated with increasingly complex behavior in mammals.

The Brain Stem and Midbrain

The brain stem is the smallest and from an evolutionary viewpoint, the oldest and most primitive part of the brain. The brain stem is continuous with the spinal cord, and is composed of the parts of the hindbrain and midbrain. The medulla oblongata and pons control heart rate, constriction of blood vessels, digestion and respiration.

The midbrain consists of connections between the hindbrain and forebrain. Mammals use this part of the brain only for eye reflexes.

The Cerebellum

The cerebellum is the third part of the hindbrain, but it is not considered part of the brain stem. Functions of the cerebellum include fine motor coordination and body movement, posture, and balance. This region of the brain is enlarged in birds and controls muscle action needed for flight.

The Forebrain

The forebrain consists of the diencephalon and cerebrum. The thalamus and hypothalamus are the parts of the diencephalon. The thalamus acts as a switching center for nerve messages. The hypothalamus is a major homeostatic center having both nervous and endocrine functions.

The cerebrum, the largest part of the human brain, is divided into left and right hemispheres connected to each other by the corpus callosum. The hemispheres are covered by a thin layer of gray matter known as the cerebral cortex, the most recently evolved region of the vertebrate brain. Fish have no cerebral cortex, amphibians and reptiles have only rudiments of this area.

The cortex in each hemisphere of the cerebrum is between 1 and 4 mm thick. Folds divide the cortex into four lobes: occipital, temporal, parietal, and frontal. No region of the brain functions alone, although major functions of various parts of the lobes have been determined.

The occipital lobe (back of the head) receives and processes visual information. The temporal lobe receives auditory signals, processing language and the meaning of words. The parietal lobe is associated with the sensory cortex and processes information about touch, taste, pressure, pain, and heat and cold. The frontal lobe conducts three functions:

1. motor activity and integration of muscle activity
2. speech
3. thought processes

Most people who have been studied have their language and speech areas on the left hemisphere of their brain. Language comprehension is found in Wernicke's area. Speaking ability is in Broca's area. Damage to Broca's area causes speech impairment but not impairment of language comprehension. Lesions in Wernicke's area impairs ability to comprehend written and spoken words but not speech. The remaining parts of the cortex are associated with higher thought processes, planning, memory, personality and other human activities.

The Spinal Cord:

The Spinal Cord is connected to the brain and is about the diameter of a human finger. From the brain the spinal cord descends down the middle of the back and is surrounded and protected by the bony vertebral column. The spinal cord is surrounded by a clear fluid called Cerebral Spinal Fluid (CSF), that acts as a cushion to protect the delicate nerve tissues against damage from banging against the inside of the vertebrae.

The anatomy of the spinal cord itself, consists of millions of nerve fibres which transmit electrical information to and from the limbs, trunk and organs of the body, back to and from the brain. The brain and spinal cord are referred to as the Central Nervous System, whilst the nerves connecting the spinal cord to the body are referred to as the Peripheral Nervous System.

The nerves within the spinal cord are grouped together in different bundles called Ascending and Descending tracts.

Ascending tracts within the spinal cord carry information from the body, upwards to the brain, such as touch, skin temperature, pain and joint position.

Descending tracts within the spinal cord carry information from the brain downwards to initiate movement and control body functions.

Nerves called the spinal nerves or nerve roots come off the spinal cord and pass out through a hole in each of the vertebrae called the Foramen to carry the information from the spinal cord to the rest of the body, and from the body back up to the brain

There are four main groups of spinal nerves which exit different levels of the spinal cord.

These are in descending order down the vertebral column:

Cervical Nerves "C" : (nerves in the neck) supply movement and feeling to the arms, neck and upper trunk.

Thoracic Nerves "T" : (nerves in the upper back) supply the trunk and abdomen.

Lumbar Nerves "L" and Sacral Nerves "S" : (nerves in the lower back) supply the legs, the bladder, bowel and sexual organs.

The spinal nerves carry information to and from different levels (segments) in the spinal cord. Both the nerves and the segments in the spinal cord are numbered in a similar way to the vertebrae. The point at which the spinal cord ends is called the conus medullaris, and is the terminal end of the spinal cord. It occurs near lumbar nerves L1 and L2. After the spinal cord terminates, the spinal nerves continue as a bundle of nerves called the cauda equina. The upper end of the conus medullaris is usually not well defined.

There are 31 pairs of spinal nerves which branch off from the spinal cord. In the cervical region of the spinal cord, the spinal nerves exit above the vertebrae. A change occurs with the C7 vertebra however, where the C8 spinal nerve exits the vertebra below the C7 vertebra. Therefore, there is an 8th cervical spinal nerve even though there is no 8th cervical vertebra. From the 1st thoracic vertebra downwards, all spinal nerves exit below their equivalent numbered vertebrae.

The spinal nerves which leave the spinal cord are numbered according to the vertebra at which they exit the spinal column. So, the spinal nerve T4, exits the spinal column through the foramen in the 4th thoracic vertebra. The spinal nerve L5 leaves the spinal cord from the conus medullaris, and travels along the cauda equina until it exits the 5th lumbar vertebra.

Drugs and the Brain

Some neurotransmitters are excitory, such as acetylcholine, norepinephrine, serotonin, and dopamine. Some are associated with relaxation, such as dopamine and serotonin. Dopamine release seems related to sensations of pleasure. Endorphins are natural opioids that produce elation and reduction of pain, as do artificial chemicals such as opium and heroin. Neurological diseases, for example Parkinson's disease and Huntington's disease, are due to imbalances of neurotransmitters. Parkinson's is due to a dopamine deficiency. Huntington's disease is thought to be cause by malfunctioning of an inhibitory neurotransmitter. Alzheimer's disease is associated with protein plaques in the brain.

Senses:

Input to the nervous system is in the form of our five senses: pain, vision, taste, smell, and hearing. Vision, taste, smell, and hearing input are the special senses. Pain, temperature, and pressure are known as somatic senses. Sensory input begins with sensors that react to stimuli in the form of energy that is transmitted into an action potential and sent to the CNS.

Sensory Receptors

• Sensory receptors are classified according to the type of energy they can detect and respond to.
• Mechanoreceptors: hearing and balance, stretching.
• Photoreceptors: light.
• Chemoreceptors: smell and taste mainly, as well as internal sensors in the digestive and circulatory systems.
• Thermoreceptors: changes in temperature.
• Electroreceptors: detect electrical currents in the surrounding environment 
• 
  Mechanoreceptors vary greatly in the specific type of stimulus and duration of stimulus/action potentials. The most adaptable vertebrate mechanoreceptor is the hair cell. Hair cells are present in the lateral line of fish. In humans and mammals hair cells are involved with detection of sound and gravity and providing balance.t.

Orientation and Gravity

Orientation and gravity are detected at the semicircular canals. Hair cells along three planes respond to shifts of liquid within the cochlea, providing a three-dimensional sense of equilibrium. Calcium carbonate crystals can shift in response to gravity, providing sensory information about gravity and acceleration

Hearing

Hearing involves the actions of the external ear, eardrum, ossicles, and cochlea. In hearing, sound waves in air are converted into vibrations of a liquid then into movement of hair cells in the cochlea. Finally they are converted into action potentials in a sensory dendrite connected to the auditory nerve. Very loud sounds can cause violent vibrations in the membrane under hair cells, causing a shearing or permanent distortion to the cells, resulting in permanent hearing loss.

Eye

In the eye, two types of photoreceptor cells are clustered on the retina, or back portion of the eye. These receptors, rods and cones, apparently evolved from hair cells. Rods detect differences in light intensity; cones detect color. Rods are more common in a circular zone near the edge of the eye. Cones occur in the center (or fovea centralis) of the retina.

Light reaching a photoreceptor causes the breakdown of the chemical rhodopsin, which in turn causes a membrane potential that is transmitted to an action potential. The action potential transfers to synapsed neurons that connect to the optic nerve. The optic nerve connects to the occipital lobe of the brain.

Photoreceptors Detect Vision and Light Sensitivity:

Humans have three types of cones, each sensitive to a different color of light: red, blue and green. Opsins are chemicals that bind to cone cells and make those cells sensitive to light of a particular wavelength (or color). Humans have three different form of opsins coded for by three genes on the X chromosome. Defects in one or more of these opsin genes can cause color blindness, usually in males. The human eye can detect light in the 400-700 nanometer (nm) range, a small portion of the electromagnetic spectrum, the visible light spectrum. Light with wavelengths shorter than 400 nm is termed ultraviolet (UV) light. Light with wavelengths longer than 700 nm is termed infrared (IR) light.

• African Plate
• Antarctic Plate
• Arabian Plate
• Australian Plate
• Caribbean Plate
• Cocos Plate
• Eurasian Plate
• Indian Plate
• Juan de Fuca Plate (Approx. 50 miles off the West coast of Washington and Oregon)
  
• Nazca Plate
• North American Plate
• Pacific Plate
• Philippine Plate
• Scotia Plate
• South American Plate

Mid-Oceanic Ridges
The mid-oceanic ridges rise 3000 meters from the ocean floor and are more than 2000 kilometers wide surpassing the Himalayas in size. The mapping of the seafloor also revealed that these huge underwater mountain ranges have a deep trench which bisects the length of the ridges and in places is more than 2000 meters deep. Research has revealed that the greatest heat flow is centered at the crests of these mid-oceanic ridges. Seismic studies show that the mid-oceanic ridges experience an elevated number of earthquakes. All these observations indicate intense geological activity at the mid-oceanic ridges.

Geomagnetic Anomalies
Over the coarse of history,  Earth's magnetic field has reversed many times. New rock formed from magma records the orientation of Earth's magnetic field at the time the magma cools. Study of the sea floor with magnometers revealed "stripes" of alternating magnetization parallel to the mid-oceanic ridges. This is evidence for continuous formation of new rock at the ridges. As more rock forms, older rock is pushed farther away from the ridge, producing symmetrical stripes to either side of the ridge. Geologists have determined that rocks found in different parts of the planet with similar ages have the same magnetic characteristics.

Deep Sea Trenches
The deepest waters are found in oceanic trenches, which plunge as deep as 35,000 feet below the ocean surface. These trenches are usually long and narrow, and run parallel to and near the oceans margins. They are often associated with and parallel to large continental mountain ranges. There is also an observed parallel association of trenches and island arcs. Like the mid-oceanic ridges, the trenches are seismically active, but unlike the ridges they have low levels of heat flow. Scientists also began to realize that the youngest regions of the ocean floor were along the mid-oceanic ridges, and that the age of the ocean floor increased as the distance from the ridges increased. In addition, it has been determined that the oldest seafloor often ends in the deep-sea trenches.

Island Arcs
Chains of islands are found throughout the oceans and especially in the western Pacific margins; the Aleutians, Kuriles, Japan, Ryukus, Philippines, Marianas, Indonesia, Solomons, New Hebrides, and the Tongas, are some examples.. These "Island arcs" are usually situated along deep sea trenches and are situated on the continental side of the trench.

These observations, along with many other studies of our planet, support the theory that underneath the Earth's crust (the lithosphere: a solid array of plates) is a malleable layer of heated rock known as the asthenosphere which is heated by radioactive decay of elements such as Uranium, Thorium, and Potassium. Because the radioactive source of heat is deep within the mantle, the fluid asthenosphere circulates as convection currents underneath the solid lithosphere. This heated layer is the source of lava we see in volcanos, the source of heat that drives hot springs and geysers, and the source of raw material which pushes up the mid-oceanic ridges and forms new ocean floor. Magma continuously wells upwards at the mid-oceanic ridges (arrows) producing currents of magma flowing in opposite directions and thus generating the forces that pull the sea floor apart at the mid-oceanic ridges. As the ocean floor is spread apart cracks appear in the middle of the ridges allowing molten magma to surface through the cracks to form the newest ocean floor. As the ocean floor moves away from the mid-oceanic ridge it will eventually come into contact with a continental plate and will be subducted underneath the continent. Finally, the lithosphere will be driven back into the asthenosphere where it returns to a heated state.

Converging Boundary:

In other converging boundaries, there is no volcanic activity because the tectonic plates are both continental plates, weighing the same. No subduction happens along these margins, just massive deformation of the edges of the plates. The Indian plate and the European plate are now creating the Himalayan Mountains, these two plates have continued slamming into each other, causing the crust to buckle, wrinkle, and uplift into the highest mountain range on earth.

A converging boundary is the opposite of a spreading boundary. Typically you will see a converging boundary on a tectonic plate that is on the opposite side of a spreading boundary. As a plate moves in one direction it collides with the adjacent plate on its front, while the trailing end of the plate is being pulled and stretched  from the plate on the other end.  The Pacific plate is presently moving north and westward  as the top edge converges with the North American and European plates.

Spreading Boundary:

Transverse Boundaries:

Transverse boundaries slide by on another. In many of these boundaries there is a lot of tension and strain where the two plates are sliding and scraping past each other. The resulting strain from the sliding action of the plates causes cracks in the crust called faults. As the larger plates move past each other some chunks of crust and overlying rock are broken into what are called fault blocks. When there is a big enough movement along the cracks or faults in the earth's crust this is the cause of earthquakes. The San Andreas fault in California is a example of this. This fault is moving at a rate of approximately 1.5 inches per year, the western boundary sliding northwest.

Subduction: 

One plate, usually the lighter continental crust rides up on top the other. Presently the South American plates are crashing into each other. The lighter continental South American plate is riding up over the heavier oceanic Nazca plate. Deep down where the leading edge of the Nazca plate is diving down under the South American plate it's making contact with the molten magma of the earth's mantle. This melts the Nazca plate margin sending magma chambers rising to the surface where they sometimes break through in volcanic eruptions. The subduction (downward) of the Nazca plate under the the South American continent is what caused the largest measurement in recorded in1960 was a 9.5 earthquake. The Nazca plate continues to dive down below the continent and it's this constant slow movement creates earthquakes throughout that region. The Chilean earthquake of 1960 sent a tsunami 9,000 miles.

The asthenosphere's elastic behaviour and low viscosity allow the overlying, more rigid plates of lithosphere to move laterally in a process known as plate tectonics. Seismic waves passing through this layer are significantly slowed. Isostatic adjustments (the depression or uplift of continents by buoyancy) take place in the asthenosphere, and magma is believed to be generated there.  Its elasticity and viscosity also allow overlying crust and mantle to move vertically in response to gravity to achieve isostatic equilibrium

A general derivation of the thrust equation shows that the amount of thrust generated depends on the mass flow through the engine and the exit velocity of the gas. Different propulsion systems generate thrust in slightly different ways.

If we think about Newton's first law of motion, we realize that an airplane propulsion system must serve two purposes. First, the thrust from the propulsion system must balance the drag of the airplane when the airplane is cruising. And second, the thrust from the propulsion system must exceed the drag of the airplane for the airplane to accelerate. In fact, the greater the difference between the thrust and the drag, called the excess thrust, the faster the airplane will accelerate.

Some aircraft, like airliners and cargo planes, spend most of their life in a cruise condition. For these airplanes, excess thrust is not as important as high engine efficiency and low fuel usage. Since thrust depends on both the amount of gas moved and the velocity, we can generate high thrust by accelerating a large mass of gas by a small amount, or by accelerating a small mass of gas by a large amount. Because of the aerodynamic efficiency of propellers and fans, it is more fuel efficient to accelerate a large mass by a small amount. That is why we find high bypass fans and turboprops on cargo planes and airliners.

Some aircraft, like fighter planes or experimental high speed aircraft, require very high excess thrust to accelerate quickly and to overcome the high drag associated with high speeds. For these airplanes, engine efficiency is not as important as very high thrust. Modern military aircraft typically employ afterburners on a low bypass turbofan core. Most likely, future hypersonic aircraft will employ some type of ramjet or rocket propulsion.

Although DNA is the carrier of genetic information in a cell, proteins do most of the work. Proteins are long chains containing as many as 20 different kinds of amino acids. Each cell contains thousands of different proteins: enzymes that make new molecules and catalyze nearly all chemical processes in cells; structural components that give cells their shape and help them move; hormones that transmit signals throughout the body; antibodies that recognize foreign molecules; and transport molecules that carry oxygen. The genetic code carried by DNA is what specifies the order and number of amino acids and, therefore, the shape and function of the protein. See DNA  or   RNA

Scientists use a wide variety of names to describe specific types of hot, dry flows of rock fragments and gas produced by erupting volcanoes. The terms below are used to describe either (1) the way in which a pyroclastic flow originates and moves; or (2) a predominant characteristic of the resulting deposit.

Ash Flow or Ash Cloud
A pyroclastic flow consisting primarily of ash-sized particles, including glass shards and mineral fragments

Block and Ash Flow
A pyroclastic flow consisting of ash and large lava fragments with few gas bubbles, which typically forms as a consequence of a collapsing lava flow or dome.

Base Surge
A turbulent, low-density flow of rock debris and water and (or) steam that moves at high speeds. Base surges may occur when an explosive eruption occurs from within a crater lake or an ocean.

Directed Blast
A volcanic explosion of rocks and magma (or both) with a low-angle component. When the rock debris from a directed blast falls to the ground, it behaves like a pyroclastic flow or surge and moves rapidly away from the volcano.

Nuée Ardente (glowing cloud)
When viewed at night or in low light, pyroclastic flows may appear to glow red. The term is widely used to describe pyroclastic flows, but not to imply the way a flow is generated.

Pumice Flow
A pyroclastic flow consisting predominantly of pumice fragments, which contain many gas bubbles.

BillNye.com

Radioactive decay rates are normally stated in terms of their half-lives**, and the half-life of a given nuclear species is related to its radiation risk. The different types of radioactivity lead to different decay paths which transmute the nuclei into other chemical elements. Examining the amounts of the decay products makes possible radioactive dating.

The half-life is the amount of time that it will take half of the atoms to decay.  This does not mean that in twice that amount of time, all the atoms will decay.  Since this is a random process, there is no history and you have to start over, so in the second half-life, half of the remaining atoms will decay, leaving a quarter of the original atoms.

Note:  All the atoms will still be there, but the ones that have decayed will be a different element.

Radiation from nuclear sources is distributed equally in all directions, obeying the inverse square law.

This means that they have a charge of +2, and a mass of 4
(the mass is measured in "atomic mass units", where each proton & neutron=1)

Alpha particles are relatively slow and heavy.

They have a low penetrating power - you can stop them with just a sheet of paper.

Because they have a large charge, alpha particles ionise other atoms strongly.

They are fast, and light.

Beta particles have a medium penetrating power - they are stopped by a sheet of aluminium or plastics such as perspex.

Beta particles ionise atoms that they pass, but not as strongly as Alpha particles do.

Gamma rays have a high penetrating power - it takes a thick sheet of metal such as lead, or concrete to reduce them significantly.

Gamma rays do not directly ionise other atoms, although they may cause atoms to emit other particles which will then cause ionisation.

We don't find pure gamma sources - gamma rays are emitted alongside alpha or beta particles. Strictly speaking, gamma emission isn't 'radioactive decay' because it doesn't change the state of the nucleus, it just carries away some energy.

Types of Radioactivity

• Alpha particles are easy to stop, gamma rays are hard to stop.
   
  
• Particles that ionise other atoms strongly have a low penetrating power, because they lose energy each time they ionise an atom.
  
  
• Radioactive decay is not affected by external conditions.

Just because something is called an isotope doesn't necessarily mean it's radioactive.
You can think of different isotopes of an atom being different "versions" of that atom.

Consider a carbon atom. It has 6 protons and 6 neutrons - we call it "carbon-12" because it has an atomic mass of 12 (6 plus 6).
If we add a neutron, it's still a carbon atom, but it's a different isotope of carbon. One useful isotope of carbon is "carbon-14", which has 6 protons and 8 neutrons. This is the atom we look for when we're carbon dating an object.

Isotopes of an atom have the same number of protons, but a different number of neutrons.

Deuterium-Tritium Fusion

Hydrogen Fusion Reactions

Even though a lot of energy is required to overcome the Coulomb barrier and initiate hydrogen fusion, the energy yields are enough to encourage continued research. Hydrogen fusion on the earth could make use of the reactions:

These reactions are more promising than the proton-proton fusion of the stars for potential energy sources. Of these the deuterium-tritium fusion appears to be the most promising and has been the subject of most experiments. In a deuterium-deuterium reactor, another reaction could also occur, creating a deuterium cycle:

Tritium Breeding

Deuterium-Tritium fusion is the most promising of the hydrogen fusion reactions, but no tritium occurs in nature since it has a 10 year half-life. The most promising source of tritium seems to be the breeding of tritium from lithium-6 by neutron bombardment with the reaction

which can be achieved by slow neutrons. This would occur if lithium were used as the coolant and heat transfer medium around the reaction chamber of a fusion reactor. Lithium-6 makes up 7.4% of natural lithium. While this constitutes a sizable supply, it is the limiting resource for the D-T process since the supply of deuterium fuel is virtually unlimited. With fast neutrons, tritium can be bred from the more abundant Li-7:

Deuterium Source

Since the most practical nuclear fusion reaction for power generation seems to be the deuterium-tritium reaction, the sources of these fuels are important. The deuterium part of the fuel does not pose a great problem because about 1 part in 5000 of the hydrogen in seawater is deuterium. This amounts to over 10^15 tons of deuterium. Viewed as a potential fuel for a fusion reactor, a gallon of seawater could produce as much energy as 300 gallons of gasoline. The tritium part of the fuel is more problematic - there is no sizable natural source since tritium is radioactive with a halflife of about 10 years. It would have to be obtained by breeding the tritium from lithium.

Nuclear Fission

Fission only happens with heavy elements.

The simplest type of fission is called alpha-decay.  A group of two protons and two neutrons (called an “alpha particle”, which is basically a helium nucleus) splits off and the rest of the nucleus remains as a whole.

Fission can also result in the nucleus splitting into a bunch of fragments of varying sizes.

Fission is sometimes called Spontaneous Fission to distinguish it from Induced Fission, which is when you hit the nucleus with a projectile such as a neutron.  Induced fission is responsible for most of the reactions in nuclear power plants and nuclear bombs.

If a massive nucleus like uranium-235 breaks apart (fissions), then there will be a net yield of energy because the sum of the masses of the fragments will be less than the mass of the uranium nucleus. If the mass of the fragments is equal to or greater than that of iron at the peak of the binding energy curve, then the nuclear particles will be more tightly bound than they were in the uranium nucleus, and that decrease in mass comes off in the form of energy according to the Einstein equation. For elements lighter than iron, fusion will yield energy.

The fission of U-235 in reactors is triggered by the absorption of a low energy neutron, often termed a "slow neutron" or a "thermal neutron". Other fissionable isotopes which can be induced to fission by slow neutrons are plutonium-239, uranium-233, and thorium-232.

Nuclear Fusion

If light nuclei are forced together, they will fuse with a yield of energy because the mass of the combination will be less than the sum of the masses of the individual nuclei. If the combined nuclear mass is less than that of iron at the peak of the binding energy curve, then the nuclear particles will be more tightly bound than they were in the lighter nuclei, and that decrease in mass comes off in the form of energy according to the Einstein relationship. For elements heavier than iron, fission will yield energy.

For potential nuclear energy sources for the Earth, the deuterium-tritium fusion reaction contained by some kind of magnetic confinement seems the most likely path. However, for the fueling of the stars, other fusion reactions will dominate.

Light Water Reactors

The nuclear fission reactors used in the United States for electric power production are classified as "light water reactors" in contrast to the "heavy water reactors" used in Canada. Light water (ordinary water) is used as the moderator in U.S. reactors as well as the cooling agent and the means by which heat is removed to produce steam for turning the turbines of the electric generators. The use of ordinary water makes it necessary to do a certain amount of enrichment of the uranium fuel before the necessary criticality of the reactor can be maintained.

The two varieties of the light water reactor are the pressurized water reactor (PWR) and boiling water reactor (BWR).

Fusion Reactors

Reactors for nuclear fusion are of two main varieties, magnetic confinement reactors and inertial confinement reactors. The strategies for creating fusion reactors are largely dictated by the fact that the temperatures involved in nuclear fusion are far too high to be contained in any material container.

The strategy of the magnetic confinement reactor is to confine the hot plasma by means of magnetic fields which keep it perpetually in looping paths which do not touch the wall of the container. This is typified by the tokamak design, the most famous example of which is the TFTR at Princeton.

The strategy of the inertial confinement reactor is to put such high energy density into a small pellet of deuterium-tritium that it fuses in such a short time that it can't move appreciably. The most advanced test reactors involve laser fusion, particularly in the Shiva and Nova reactors at Lawrence Livermore Laboratories.

Fast Breeder Reactors

Under appropriate operating conditions, the neutrons given off by fission reactions can "breed" more fuel from otherwise non-fissionable isotopes. The most common breeding reaction is that of plutonium-239 from non-fissionable uranium-238. The term "fast breeder" refers to the types of configurations which can actually produce more fissionable fuel than they use, such as the LMFBR. This scenario is possible because the non-fissionable uranium-238 is 140 times more abundant than the fissionable U-235 and can be efficiently converted into Pu-239 by the neutrons from a fission chain reaction.

France has made the largest implementation of breeder reactors ( it halted electricity production in 1996 and was closed as a commercial plant in 1997) with its large Super-Phenix reactor and an intermediate scale reactor (BN-600) on the Caspian Sea for electric power and desalinization.

A

Absolute risk: the proportion of a population expected to get a disease over a specified time period. 

Absorbed dose: the amount of energy deposited by ionizing radiation in a unit mass of tissue. It is expressed in units of joule per kilogram (J/kg), and called “gray” (Gy).

Activity (radioactivity): the rate of decay of radioactive material expressed as the number of atoms breaking down per second measured in units called becquerels or curies.

Acute exposure: an exposure to radiation that occurred in a matter of minutes rather than in longer, continuing exposure over a period of time.

Acute Radiation Syndrome (ARS): a serious illness caused by receiving a dose greater than 75 rads of penetrating radiation to the body in a short time (usually minutes). The earliest symptoms are nausea, fatigue, vomiting, and diarrhea. Hair loss, bleeding, swelling of the mouth and throat, and general loss of energy may follow. If the exposure has been approximately 1,000 rads or more, death may occur within 2 – 4 weeks.

Air burst: a nuclear weapon explosion that is high enough in the air to keep the fireball from touching the ground. Because the fireball does not reach the ground and does not pick up any surface material, the radioactivity in the fallout from an air burst is relatively insignificant compared with a surface burst.

Alpha particle: the nucleus of a helium atom, made up of two neutrons and two protons with a charge of +2. Certain radioactive nuclei emit alpha particles. Alpha particles generally carry more energy than gamma or beta particles, and deposit that energy very quickly while passing through tissue. Alpha particles can be stopped by a thin layer of light material, such as a sheet of paper, and cannot penetrate the outer, dead layer of skin. Therefore, they do not damage living tissue when outside the body. When alpha-emitting atoms are inhaled or swallowed, however, they are especially damaging because they transfer relatively large amounts of ionizing energy to living cells. 

Ambient air: the air that surrounds us.

Americium (Am): a silvery metal; it is a man-made element whose isotopes Am-237 through Am-246 are all radioactive. Am-241 is formed spontaneously by the beta decay of plutonium-241. Trace quantities of americium are widely used in smoke detectors, and as neutron sources in neutron moisture gauges.

Atom: the smallest particle of an element that can enter into a chemical reaction.

Atomic number: the total number of protons in the nucleus of an atom.

Atomic mass unit (amu): 1 amu is equal to one twelfth of the mass of a carbon-12 atom.

Atomic mass number: the total number of protons and neutrons in the nucleus of an atom.

Atomic weight: the mass of an atom, expressed in atomic mass units. For example, the atomic number of helium-4 is 2, the atomic mass is 4, and the atomic weight is 4.00026.

B

Background radiation: ionizing radiation from natural sources, such as terrestrial radiation due to radionuclides in the soil or cosmic radiation originating in outer space.

Becquerel (Bq): the amount of a radioactive material that will undergo one decay (disintegration) per second.

Beta particles: electrons ejected from the nucleus of a decaying atom. Although they can be stopped by a thin sheet of aluminum, beta particles can penetrate the dead skin layer, potentially causing burns. They can pose a serious direct or external radiation threat and can be lethal depending on the amount received. They also pose a serious internal radiation threat if beta-emitting atoms are ingested or inhaled. 

Bioassay: an assessment of radioactive materials that may be present inside a person’s body through analysis of the person’s blood, urine, feces, or sweat.

Biological Effects of Ionizing Radiation (BEIR) Reports: reports of the National Research Council's committee on the Biological Effects of Ionizing Radiation.

Biological half-life: the time required for one half of the amount of a substance, such as a radionuclide, to be expelled from the body by natural metabolic processes, not counting radioactive decay, once it has been taken in through inhalation, ingestion, or absorption. .

C

Carcinogen: a cancer-causing substance.

Chain reaction: a process that initiates its own repetition. In a fission chain reaction, a fissile nucleus absorbs a neutron and fissions (splits) spontaneously, releasing additional neutrons. These, in turn, can be absorbed by other fissile nuclei, releasing still more neutrons. A fission chain reaction is self-sustaining when the number of neutrons released in a given time equals or exceeds the number of neutrons lost by absorption in non-fissile material or by escape from the system.

Chronic exposure: exposure to a substance over a long period of time, possibly resulting in adverse health effects. 

Cobalt (Co): gray, hard, magnetic, and somewhat malleable metal. Cobalt is relatively rare and generally obtained as a byproduct of other metals, such as copper. Its most common radioisotope, cobalt-60 (Co-60), is used in radiography and medical applications. Cobalt-60 emits beta particles and gamma rays during radioactive decay.

Collective dose: the estimated dose for an area or region multiplied by the estimated population in that area or region.

Committed dose: a dose that accounts for continuing exposures expected to be received over a long period of time (such as 30, 50, or 70 years) from radioactive materials that were deposited inside the body.

Contamination (radioactive): the deposition of unwanted radioactive material on the surfaces of structures, areas, objects, or people where it may be external or internal. 

Cosmic radiation: radiation produced in outer space when heavy particles from other galaxies (nuclei of all known natural elements) bombard the earth. 

Criticality: a fission process where the neutron production rate equals the neutron loss rate to absorption or leakage. A nuclear reactor is "critical" when it is operating.

Critical mass: the minimum amount of fissile material that can achieve a self-sustaining nuclear chain reaction.

Cumulative dose: the total dose resulting from repeated or continuous exposures of the same portion of the body, or of the whole body, to ionizing radiation.

Curie (Ci): the traditional measure of radioactivity based on the observed decay rate of 1 gram of radium. One curie of radioactive material will have 37 billion disintegrations in 1 second.

Cutaneous Radiation Syndrome (CRS): the complex syndrome resulting from radiation exposure of more than 200 rads to the skin. The immediate effects can be reddening and swelling of the exposed area (like a severe burn), blisters, ulcers on the skin, hair loss, and severe pain. Very large doses can result in permanent hair loss, scarring, altered skin color, deterioration of the affected body part, and death of the affected tissue (requiring surgery).

D

Decay chain (decay series): the series of decays that certain radioisotopes go through before reaching a stable form. For example, the decay chain that begins with uranium-238 (U-238) ends in lead-206 (Pb-206), after forming isotopes, such as uranium-234 (U-234), thorium-230 (Th-230), radium-226 (Ra-226), and radon-222 (Rn-222).

Decay constant: the fraction of a number of atoms of a radioactive nuclide that disintegrates in a unit of time. The decay constant is inversely proportional to the radioactive half-life.

Decay products (or daughter products): the isotopes or elements formed and the particles and high-energy electromagnetic radiation emitted by the nuclei of radionuclides during radioactive decay. Also known as "decay chain products" or "progeny" (the isotopes and elements). A decay product may be either radioactive or stable.

Decay, radioactive: disintegration of the nucleus of an unstable atom by the release of radiation.

Decontamination: the reduction or removal of radioactive contamination from a structure, object, or person.

Depleted uranium: uranium containing less than 0.7% uranium-235, the amount found in natural uranium. .

Deposition density: the activity of a radionuclide per unit area of ground. Reported as becquerels per square meter or curies per square meter.

Deterministic effects: effects that can be related directly to the radiation dose received. The severity increases as the dose increases. A deterministic effect typically has a threshold below which the effect will not occur. See also stochastic effect, non-stochastic effect.

Deuterium: a non-radioactive isotope of the hydrogen atom that contains a neutron in its nucleus in addition to the one proton normally seen in hydrogen. A deuterium atom is twice as heavy as normal hydrogen. See also tritium.

Dirty bomb: a device designed to spread radioactive material by conventional explosives when the bomb explodes. A dirty bomb kills or injures people through the initial blast of the conventional explosive and spreads radioactive contamination over possibly a large area—hence the term “dirty.” Such bombs could be miniature devices or large truck bombs. A dirty bomb is much simpler to make than a true nuclear weapon. 

Dose (radiation): radiation absorbed by person’s body. Several different terms describe radiation dose. For more information, see “Primer on Radiation Measurement” at the end of this document.

Dose coefficient: the factor used to convert radionuclide intake to dose. Usually expressed as dose per unit intake (e.g., sieverts per becquerel).

Dose equivalent: a quantity used in radiation protection to place all radiation on a common scale for calculating tissue damage. Dose equivalent is the absorbed dose in grays times the quality factor. The quality factor accounts for differences in radiation effects caused by different types of ionizing radiation. Some radiation, including alpha particles, causes a greater amount of damage per unit of absorbed dose than other radiation. The sievert (Sv) is the unit used to measure dose equivalent. For more information, see “Primer on Radiation Measurement” at the end of this document.

Dose rate: the radiation dose delivered per unit of time.

Dose reconstruction: a scientific study that estimates doses to people from releases of radioactivity or other pollutants. The dose is reconstructed by determining the amount of material released, the way people came in contact with it, and the amount they absorbed.

Dosimeter: a small portable instrument (such as a film badge, thermoluminescent dosimeter [TLD], or pocket dosimeter) for measuring and recording the total accumulated dose of ionizing radiation a person receives.

Dosimetry: assessment (by measurement or calculation) of radiation dose.

E

Effective dose: a dosimetric quantity useful for comparing the overall health affects of irradiation of the whole body. It takes into account the absorbed doses received by various organs and tissues and weighs them according to present knowledge of the sensitivity of each organ to radiation. It also accounts for the type of radiation and the potential for each type to inflict biologic damage. The effective dose is used, for example, to compare the overall health detriments of different radionuclides in a given mix. The unit of effective dose is the sievert (Sv); 1 Sv = 1 J/kg.

Effective half-life: the time required for the amount of a radionuclide deposited in a living organism to be diminished by 50% as a result of the combined action of radioactive decay and biologic elimination. 

Electron: an elementary particle with a negative electrical charge and a mass 1/1837 that of the proton. Electrons surround the nucleus of an atom because of the attraction between their negative charge and the positive charge of the nucleus. A stable atom will have as many electrons as it has protons. The number of electrons that orbit an atom determine its chemical properties. 

Element: 1) all isotopes of an atom that contain the same number of protons. For example, the element uranium has 92 protons, and the different isotopes of this element may contain 134 to 148 neutrons. 2) In a reactor, a fuel element is a metal rod containing the fissile material.

Enriched uranium: uranium in which the proportion of the isotope uranium-235 has been increased by removing uranium-238 mechanically. 

Exposure pathway: a route by which a radionuclide or other toxic material can enter the body. The main exposure routes are inhalation, ingestion, absorption through the skin, and entry through a cut or wound in the skin.

Exposure rate: a measure of the ionization produced in air by x-rays or gamma rays per unit of time (frequently expressed in roentgens per hour).

External exposure: exposure to radiation outside of the body.

F

Fallout, nuclear: minute particles of radioactive debris that descend slowly from the atmosphere after a nuclear explosion.

Fissile material: any material in which neutrons can cause a fission reaction. The three primary fissile materials are uranium-233, uranium-235, and plutonium-239.

Fission (fissioning): the splitting of a nucleus into at least two other nuclei that releases a large amount of energy. Two or three neutrons are usually released during this transformation. See also fusion.

Fractionated exposure: exposure to radiation that occurs in several small acute exposures, rather than continuously as in a chronic exposure.

Fusion: a reaction in which at least one heavier, more stable nucleus is produced from two lighter, less stable nuclei. Reactions of this type are responsible for the release of energy in stars or in thermonuclear weapons.

G

Gamma rays: high-energy electromagnetic radiation emitted by certain radionuclides when their nuclei transition from a higher to a lower energy state. These rays have high energy and a short wave length. All gamma rays emitted from a given isotope have the same energy, a characteristic that enables scientists to identify which gamma emitters are present in a sample. Gamma rays penetrate tissue farther than do beta or alpha particles, but leave a lower concentration of ions in their path to potentially cause cell damage. Gamma rays are very similar to x-rays. 

Geiger counter: a radiation detection and measuring instrument consisting of a gas-filled tube containing electrodes, between which an electrical voltage but no current flows. When ionizing radiation passes through the tube, a short, intense pulse of current passes from the negative electrode to the positive electrode and is measured or counted. The number of pulses per second measures the intensity of the radiation field. Geiger counters are the most commonly used portable radiation detection instruments.

Genetic effects: hereditary effects (mutations) that can be passed on through reproduction because of changes in sperm or ova. 

Gray (Gy): a unit of measurement for absorbed dose. It measures the amount of energy absorbed in a material. The unit Gy can be used for any type of radiation, but it does not describe the biological effects of the different radiations.

Half-life: the time any substance takes to decay by half of its original amount. 

High-level radioactive waste: the radioactive material resulting from spent nuclear fuel reprocessing. This can include liquid waste directly produced in reprocessing or any solid material derived from the liquid wastes having a sufficient concentration of fission products. Other radioactive materials can be designated as high-level waste, if they require permanent isolation. This determination is made by the U.S. Nuclear Regulatory Commission on the basis of criteria established in U.S. law. 

Hot spot: any place where the level of radioactive contamination is considerably greater than the area around it.

I

Ingestion: 1) the act of swallowing; 2) in the case of radionuclides or chemicals, swallowing radionuclides or chemicals by eating or drinking.

Inhalation: 1) the act of breathing in; 2) in the case of radionuclides or chemicals, breathing in radionuclides or chemicals.

Internal exposure: exposure to radioactive material taken into the body.

Iodine: a nonmetallic solid element. There are both radioactive and non-radioactive isotopes of iodine. Radioactive isotopes of iodine are widely used in medical applications. Radioactive iodine is a fission product and is the largest contributor to people’s radiation dose after an accident at a nuclear reactor.

Ion: an atom that has fewer or more electrons than it has protons causing it to have an electrical charge and, therefore, be chemically reactive.

Ionization: the process of adding one or more electrons to, or removing one or more electrons from, atoms or molecules, thereby creating ions. High temperatures, electrical discharges, or nuclear radiation can cause ionization.

Ionizing radiation: any radiation capable of displacing electrons from atoms, thereby producing ions. High doses of ionizing radiation may produce severe skin or tissue damage. See also alpha particle, beta particle, gamma ray, neutron, x-ray.

Irradiation: exposure to radiation.

Isotope: a nuclide of an element having the same number of protons but a different number of neutrons.

K

Kiloton (Kt): the energy of an explosion that is equivalent to an explosion of 1,000 tons of TNT. One kiloton equals 1 trillion (1012) calories. See also megaton.

L

Latent period: the time between exposure to a toxic material and the appearance of a resultant health effect.

Lead (Pb): a heavy metal. Several isotopes of lead, such as Pb-210 which emits beta radiation, are in the uranium decay chain.

Local radiation injury (LRI): acute radiation exposure (more than 1,000 rads) to a small, localized part of the body. Most local radiation injuries do not cause death. However, if the exposure is from penetrating radiation (neutrons, x-rays, or gamma rays), internal organs may be damaged and some symptoms of acute radiation syndrome (ARS), including death, may occur. Local radiation injury invariably involves skin damage, and a skin graft or other surgery may be required. 

Low-level waste (LLW): radioactively contaminated industrial or research waste such as paper, rags, plastic bags, medical waste, and water-treatment residues. It is waste that does not meet the criteria for any of three other categories of radioactive waste: spent nuclear fuel and high-level radioactive waste; transuranic radioactive waste; or uranium mill tailings. Its categorization does not depend on the level of radioactivity it contains.

M

Megaton (Mt): the energy of an explosion that is equivalent to an explosion of 1 million tons of TNT. One megaton is equal to a quintillion (1018) calories. See also kiloton.

Molecule: a combination of two or more atoms that are chemically bonded. A molecule is the smallest unit of a compound that can exist by itself and retain all of its chemical properties.

N

Neoplastic: pertaining to the pathologic process resulting in the formation and growth of an abnormal mass of tissue.

Neutron: a small atomic particle possessing no electrical charge typically found within an atom's nucleus. Neutrons are, as the name implies, neutral in their charge. That is, they have neither a positive nor a negative charge. A neutron has about the same mass as a proton. See also alpha particle, beta particle, gamma ray, nucleon, x-ray.

Non-ionizing radiation: radiation that has lower energy levels and longer wavelengths than ionizing radiation. It is not strong enough to affect the structure of atoms it contacts but is strong enough to heat tissue and can cause harmful biological effects. Examples include radio waves, microwaves, visible light, and infrared from a heat lamp.

Non-stochastic effects: effects that can be related directly to the radiation dose received. The effect is more severe with a higher dose. It typically has a threshold, below which the effect will not occur. These are sometimes called deterministic effects. For example, a skin burn from radiation is a non-stochastic effect that worsens as the radiation dose increases. See also stochastic effects.

Nuclear energy: the heat energy produced by the process of nuclear fission within a nuclear reactor or by radioactive decay.

Nuclear fuel cycle: the steps involved in supplying fuel for nuclear power plants. It can include mining, milling, isotopic enrichment, fabrication of fuel elements, use in reactors, chemical reprocessing to recover the fissile material remaining in the spent fuel, reenrichment of the fuel material refabrication into new fuel elements, and waste disposal.

Nuclear tracers: radioisotopes that give doctors the ability to "look" inside the body and observe soft tissues and organs, in a manner similar to the way x-rays provide images of bones. A radioactive tracer is chemically attached to a compound that will concentrate naturally in an organ or tissue so that an image can be taken.

Nucleon: a proton or a neutron; a constituent of the nucleus of an atom.

Nucleus: the central part of an atom that contains protons and neutrons. The nucleus is the heaviest part of the atom.

Nuclide: a general term applicable to all atomic forms of an element. Nuclides are characterized by the number of protons and neutrons in the nucleus, as well as by the amount of energy contained within the atom.

P

Pathways: the routes by which people are exposed to radiation or other contaminants. The three basic pathways are inhalation, ingestion, and direct external exposure. 

Penetrating radiation: radiation that can penetrate the skin and reach internal organs and tissues. Photons (gamma rays and x-rays), neutrons, and protons are penetrating radiations. However, alpha particles and all but extremely high-energy beta particles are not considered penetrating radiation.

Photon: discrete "packet" of pure electromagnetic energy. Photons have no mass and travel at the speed of light. The term "photon" was developed to describe energy when it acts like a particle (causing interactions at the molecular or atomic level), rather than a wave. Gamma rays and x-rays are photons.

Pitchblende: a brown to black mineral that has a distinctive luster. It consists mainly of urananite (UO2), but also contains radium (Ra). It is the main source of uranium (U) ore.

Plume: the material spreading from a particular source and traveling through environmental media, such as air or ground water. For example, a plume could describe the dispersal of particles, gases, vapors, and aerosols in the atmosphere, or the movement of contamination through an aquifer (For example, dilution, mixing, or adsorption onto soil).

Plutonium (Pu): a heavy, man-made, radioactive metallic element. The most important isotope is Pu-239, which has a half-life of 24,000 years. Pu-239 can be used in reactor fuel and is the primary isotope in weapons. One kilogram is equivalent to about 22 million kilowatt-hours of heat energy. The complete detonation of a kilogram of plutonium produces an explosion equal to about 20,000 tons of chemical explosive. All isotopes of plutonium are readily absorbed by the bones and can be lethal depending on the dose and exposure time.

Polonium (Po): a radioactive chemical element and a product of radium (Ra) decay. Polonium is found in uranium (U) ores.

Prenatal radiation exposure: radiation exposure to an embryo or fetus while it is still in its mother’s womb. At certain stages of the pregnancy, the fetus is particularly sensitive to radiation and the health consequences could be severe above 5 rads, especially to brain function.

Proton: a small atomic particle, typically found within an atom's nucleus, that possesses a positive electrical charge. Even though protons and neutrons are about 2,000 times heavier than electrons, they are tiny. The number of protons is unique for each chemical element. See also nucleon.

Q

Quality factor (Q): the factor by which the absorbed dose (rad or gray) is multiplied to obtain a quantity that expresses, on a common scale for all ionizing radiation, the biological damage (rem) to an exposed person. It is used because some types of radiation, such as alpha particles, are more biologically damaging internally than other types.

R

Rad (radiation absorbed dose): a basic unit of absorbed radiation dose. It is a measure of the amount of energy absorbed by the body. The rad is the traditional unit of absorbed dose. It is being replaced by the unit gray (Gy), which is equivalent to 100 rad. One rad equals the dose delivered to an object of 100 ergs of energy per gram of material.

Radiation: energy moving in the form of particles or waves. Familiar radiations are heat, light, radio waves, and microwaves. Ionizing radiation is a very high-energy form of electromagnetic radiation.

Radiation sickness: See also acute radiation syndrome (ARS), or the CDC fact sheet “Acute Radiation Syndrome,” at emergency.cdc.gov/radiation/ars.asp.

Radiation warning symbol: a symbol prescribed by the Code of Federal Regulations. It is a magenta or black trefoil on a yellow background. It must be displayed where certain quantities of radioactive materials are present or where certain doses of radiation could be received.

Radioactive contamination: the deposition of unwanted radioactive material on the surfaces of structures, areas, objects, or people. It can be airborne, external, or internal. 

Radioactive decay: the spontaneous disintegration of the nucleus of an atom.

Radioactive half-life: the time required for a quantity of a radioisotope to decay by half. For example, because the half-life of iodine-131 (I-131) is 8 days, a sample of I-131 that has 10 mCi of activity on January 1, will have 5 mCi of activity 8 days later, on January 9. 

Radioactivity: the process of spontaneous transformation of the nucleus, generally with the emission of alpha or beta particles often accompanied by gamma rays. This process is referred to as decay or disintegration of an atom.

Radiogenic: health effects caused by exposure to ionizing radiation.

Radiography: 1) medical: the use of radiant energy (such as x-rays and gamma rays) to image body systems. 2) industrial: the use of radioactive sources to photograph internal structures, such as turbine blades in jet engines. A sealed radiation source, usually iridium-192 (Ir-192) or cobalt-60 (Co-60), beams gamma rays at the object to be checked. Gamma rays passing through flaws in the metal or incomplete welds strike special photographic film (radiographic film) on the opposite side.

Radioisotope (radioactive isotope): isotopes of an element that have an unstable nucleus. Radioactive isotopes are commonly used in science, industry, and medicine. The nucleus eventually reaches a stable number of protons and neutrons through one or more radioactive decays. Approximately 3,700 natural and artificial radioisotopes have been identified.

Radiological or radiologic: related to radioactive materials or radiation. The radiological sciences focus on the measurement and effects of radiation.

Radiological dispersal device (RDD): a device that disperses radioactive material by conventional explosive or other mechanical means, such as a spray. See also dirty bomb.

Radionuclide: an unstable and therefore radioactive form of a nuclide.

Radium (Ra): a naturally occurring radioactive metal. Radium is a radionuclide formed by the decay of uranium (U) and thorium (Th) in the environment. It occurs at low levels in virtually all rock, soil, water, plants, and animals. Radon (Rn) is a decay product of radium.

Radon (Rn): a naturally occurring radioactive gas found in soils, rock, and water throughout the United States. Radon causes lung cancer and is a threat to health because it tends to collect in homes, sometimes to very high concentrations. As a result, radon is the largest source of exposure to people from naturally occurring radiation.

Relative risk: the ratio between the risk for disease in an irradiated population to the risk in an unexposed population. A relative risk of 1.1 indicates a 10% increase in cancer from radiation, compared with the "normal" incidence. 

Rem (roentgen equivalent, man): a unit of equivalent dose. Not all radiation has the same biological effect, even for the same amount of absorbed dose. Rem relates the absorbed dose in human tissue to the effective biological damage of the radiation. It is determined by multiplying the number of rads by the quality factor, a number reflecting the potential damage caused by the particular type of radiation. The rem is the traditional unit of equivalent dose, but it is being replaced by the sievert (Sv), which is equal to 100 rem.

S

Sensitivity: ability of an analytical method to detect small concentrations of radioactive material.

Shielding: the material between a radiation source and a potentially exposed person that reduces exposure.

Sievert (Sv): a unit used to derive a quantity called dose equivalent. This relates the absorbed dose in human tissue to the effective biological damage of the radiation. Not all radiation has the same biological effect, even for the same amount of absorbed dose. Dose equivalent is often expressed as millionths of a sievert, or micro-sieverts (µSv). One sievert is equivalent to 100 rem.

S.I. units: the Systeme Internationale (or International System) of units and measurements. This system of units officially came into being in October 1960 and has been adopted by nearly all countries, although the amount of actual usage varies considerably.

Somatic effects: effects of radiation that are limited to the exposed person, as distinguished from genetic effects, which may also affect subsequent generations. See also teratogenic effects.

Stable nucleus: the nucleus of an atom in which the forces among its particles are balanced. See also unstable nucleus.

Stochastic effect: effect that occurs on a random basis independent of the size of dose. The effect typically has no threshold and is based on probabilities, with the chances of seeing the effect increasing with dose. If it occurs, the severity of a stochastic effect is independent of the dose received. Cancer is a stochastic effect. S

Strontium (Sr): a silvery, soft metal that rapidly turns yellow in air. Sr-90 is one of the radioactive fission materials created within a nuclear reactor during its operation. Stronium-90 emits beta particles during radioactive decay.

Surface burst: a nuclear weapon explosion that is close enough to the ground for the radius of the fireball to vaporize surface material. Fallout from a surface burst contains very high levels of radioactivity. 

T

Tailings: waste rock from mining operations that contains concentrations of mineral ore that are too low to make typical extraction methods economical.

Thermonuclear device: a “hydrogen bomb.” A device with explosive energy that comes from fusion of small nuclei, as well as fission.

Teratogenic effect: birth defects that are not passed on to future generations, caused by exposure to a toxin as a fetus. See also genetic effects, somatic effects.

Terrestrial radiation: radiation emitted by naturally occurring radioactive materials, such as uranium (U), thorium (Th), and radon (Rn) in the earth.

Thorium (Th): a naturally occurring radioactive metal found in small amounts in soil, rocks, water, plants, and animals. The most common isotopes of thorium are thorium-232 (Th-232), thorium-230 (Th-230), and thorium-238 (Th-238).

Transuranic: pertaining to elements with atomic numbers higher than uranium (92). For example, plutonium (Pu) and americium (Am) are transuranics.

Tritium: (chemical symbol H-3) a radioactive isotope of the element hydrogen (chemical symbol H). 

U

Unstable nucleus: a nucleus that contains an uneven number of protons and neutrons and seeks to reach equilibrium between them through radioactive decay (i.e., the nucleus of a radioactive atom). See also stable nucleus.

Uranium (U): a naturally occurring radioactive element whose principal isotopes are uranium-238 (U-238) and uranium-235 (U-235). Natural uranium is a hard, silvery-white, shiny metallic ore that contains a minute amount of uranium-234 (U-234).

Uranium mill tailings: naturally radioactive residue from the processing of uranium ore. Although the milling process recovers about 95% of the uranium, the residues, or tailings, contain several isotopes of naturally occurring radioactive material, including uranium (U), thorium (Th), radium (Ra), polonium (Po), and radon (Rn).

W

Whole body count: the measure and analysis of the radiation being emitted from a person’s entire body, detected by a counter external to the body.

Whole body exposure: an exposure of the body to radiation, in which the entire body, rather than an isolated part, is irradiated by an external source.

X

X-ray: electromagnetic radiation caused by deflection of electrons from their original paths, or inner orbital electrons that change their orbital levels around the atomic nucleus. X-rays, like gamma rays can travel long distances through air and most other materials. Like gamma rays, x-rays require more shielding to reduce their intensity than do beta or alpha particles. X-rays and gamma rays differ primarily in their origin: x-rays originate in the electronic shell; gamma rays originate in the nucleus. See also neutron.