Chain reaction - A self-sustaining nuclear
reaction; a series of nuclear fissions in which neutrons released by splitting
one atom leads to the splitting of others.
Clean Weapon - One in which measures have been taken
to reduce the amount of residual radioactivity relative to a "normal"
weapon of the same energy yield.
Cloud Chamber Effect - See Condensation cloud.
Cloud Column - The visible column of weapon debris (and
possibly dust and water droplets) extending upward from the point of burst
of a nuclear (or atomic) weapon. See Radioactive cloud.
Cloud Phenomena - See Base surge, Cloud column, Fireball,
Column (or Plume) - A hollow cylinder of water and spray
thrown up from an underwater burst or a nuclear (or atomic) weapon, through
which the hot, high pressure gases formed in the explosion are vented
to the atmosphere. A somewhat similar column of dirt is formed in an underground
Compton Current - Electron current generated as a result
of Compton processes. See Compton effect, Compton electron.
Compton Effect - The scattering of photons (of gamma
or X rays) by the orbital electrons of atoms. In a collision between a
(primary) photon and an electron , some of the energy of the photon is
transferred to the electron which is generally ejected from the atom.
Another (secondary) photon, with less energy, then moves off in a new
direction at an angle to the direction of motion of the primary photon.
Compton Electron - An electron of increased energy ejected
from an atom as a result of a Compton interaction with a photon. See Compton
Condensation Cloud - A mist or fog of minute water droplets
which temporarily surround the fireball following a nuclear (or atomic)
detonation in a comparatively humid atmosphere. The expansion of the air
in the negative phase of the blast wave from the explosion results in
a lowering of the temperature, so that condensation of water vapor present
in the air occurs and a cloud forms. The cloud is soon dispelled when
the pressure returns to normal and the air warms up again. The phenomenon
is similar to that used by physicists in the Wilson cloud chamber and
is sometimes called the cloud chamber effect.
Conflagration - A massive fire that occurs after a nuclear
explosion, in which the flames spread along a common front. See also firestorm.
Contact Surface Burst - See Surface burst.
Contained Underground Burst - An underground detonation
at such a depth that none of the radioactive residues escapes through
the surface of the ground.
Contamination - The deposit and/or absorption of radioactive
material, biological, or chemical agents or hazardous materials on, and
by, structures, areas, people, or objects. In the case of a nuclear (or
atomic) explosion, the material generally consists of fallout in which
fission products and other weapon debris have become incorporated with
particles of dirt, etc. Contamination can also arise from the radioactivity
induced in certain substances by the action of neutrons from a nuclear
explosion. See Decontamination, Fallout, Induced radioactivity, Weapon
Crack - The light-colored region which follows closely
behind the dark slick in an underwater burst. It is probably caused by
the reflection of the water shock wave at the surface. See Slick.
Crater. The pit, depression or cavity formed in the surface
of the earth by a surface or underground explosion. Crater formation can
occur by vaporization of the surface material, by the scouring effect
of air blast, by throwout of disturbed material, or by subsidence. In
general, the major mechanism changes from one to the next with increasing
dept of burst. The apparent crater is the depression which is seen after
the burst; it is smaller than the true crater (i.e., the cavity actually
formed by the explosion), because it is covered with a layer of loose
earth, rock, etc. See also surface burst.
Critical Mass- The minimum mass of a fissionable material
that will just maintain a fission chain reaction under precisely specified
condition, such as the nature of the material and its purity, the nature
and thickness of the tamper (or neutron reflector), the density (or compression),
and the physical shape or geometry. For an explosion to occur, the system
must be supercritical (i.e., the mass of the material must exceed the
critical mass under the existing conditions). See supercritical.
Cube Root Law - A scaling law applicable to many blast
phenomena. It relates the time and distance at which a given blast effect
is observed to the cube root of the energy yield of the explosion.
Cumulative Dose (Radiation) - The total dose resulting
from repeated exposure to radiation in the same region, or of the whole
Curie - A unit of radioactivity; it is the activity of
a quantity of any radioactive species in which 3.700 x 1010
nuclear disintegrations occur per second. The gamma curie is
sometimes defined correspondingly as the activity of material in which
this number of gamma-ray photons are emitted per second.
Damage Criteria - Standards or measures used in estimating
specific levels of damage.
Debris - See Weapon debris.
Decay (or Radioactive decay) - The decrease
in activity of any radioactive material with the passage of time due to
the spontaneous emission from the atomic nuclei of either alpha or beta
particles, sometimes accompanied by gamma radiation. See Half-life,
Decay Curve - The representation by means of a graph
of the decrease of radioactivity with respect to time.
Decontamination - The reduction of removal of contaminating
radioactive material from a structure, area, object or person. Decontamination
may be accomplished by (1) treating the surface so as to remove or decrease
the contamination; (2) letting the material stand so that the radioactivity
is decreased as a result of natural decay; and (3) covering the contamination
so as to attenuate the radiation emitted. Radioactive material removed
in process (1) must be disposed of by burial in land or sea, or in other
Delayed Fallout - See Fallout.
Deuterium - An isotope of hydrogen of mass 2 units; it
is sometimes referred to as heavy hydrogen. It can be used in thermonuclear
fusion reactions for the release of energy. Deuterium is extracted from
water which always contains 1 atom of deuterium to about 6,500 atoms of
ordinary (light) hydrogen. See Fusion, Isotope, Thermonuclear.
Diffraction - The bending of waves around the edges of
objects. In connection with a blast wave impinging on a structure, diffraction
refers to the passage around and envelopment of the structure by the blast
wave. Diffraction loading is the force (or loading) on the structure
during the envelopment process.
Direct Radiation - The nuclear radiation, composed mainly
of gamma rays and neutrons, that occurs immediately at the time of detonation.
It is usually very intense, but its range is limited to a few miles around
the center of the explosion. Also known as prompt radiation.
Disaster Control - Measures taken before, during, or
after hostile action, natural or man-made disasters, to reduce the probability
of damage, minimize its effects, and initiate recovery.
Dome - The mound of water spray thrown up into the air
when the shock wave from an underwater detonation of a nuclear (or atomic)
weapon reaches the surface.
Dosage - see Dose.
Dose - A total (or accumulated) quantity of ionizing
(or nuclear) radiation. The absorbed dose in rads represents
the amount of energy absorbed from the radiation per gram of specified
absorbing material. In soft body tissue the absorbed dose in rads is essentially
equal to the exposure in roentgens. The biological dose (also called the
RBE dose) in rems is a measure of biological effectiveness of
the absorbed radiation.See Exposure, Rad, RBE, Rem, Roentgen.
Dose Equivalent - In radiation protection associated
with peacetime nuclear activities, the dose equivalent in rems is a measure
of the biological effectiveness of absorbed ionized radiation. It is similar
to the biological dose which is used in connection with the large radiation
exposures that might accompany a nuclear explosion. See Dose, Rem.
Dose Rate - As a general rule, the amount of ionizing
(or nuclear) radiation which an individual or material would receive per
unit of time. It is usually expressed as rads (or rems) per hour or in
multiples or submultiples of these units, such as millirads per hour.
The dose rate is commonly used to indicate the level of radioactivity
in a contaminated area. See Survey meter.
Dose Rate Contour Line - A line on a map, diagram, or
overlay joining all points at which the radiation dose rate at a given
time is the same.
Dosimeter - An instrument for measuring and registering
the total accumulated dose of (or exposure to) ionizing radiations. Instruments
worn or carried by individuals are calledPersonal dosimeters.
Dosimetry - The theory and application of the principles
and techniques involved in the measurement and recording of radiation
doses and dose rates. Its practical aspect is concerned with the use of
various types of radiation instruments with which measurements are made.
See Dosimeter, Survey meter.
Drag Loading - The force of an object or structure due
to the transient winds accompanying the passage of a blast wave. The drag
pressure is the product of the dynamic pressure and the drag coefficient
which is dependent upon the shape (or geometry) of the structure or object.
See Dynamic pressure.
Dynamic Pressure - The air pressure which results from
the mass air flow (or wind) behind the shock front of a blast wave. It
is equal to the product of half the density of air through which the blast
wave passes and the square of the particle (or wind) velocity behind the
shock front as it impinges on the object or structure. See also overpressure.
Early Fallout - See fallout.
Effective Half-life - See Half-life.
Elastic Range - The stress range in which a material
will recover its original form when the force (or loading) is removed.
Elastic deformation refers to dimensional changes occurring within
the elastic range. See Plastic range.
Elastic Zone - The zone beyond the plastic zone in crater
formation in which the ground is disturbed by the explosion but returns
to its original condition.
Electromagnetic Pulse (EMP) - A sharp pulse of radio
frequency (long wavelength) electromagnetic radiation produced when an
explosion occurs in an asymmetrical environment, especially at or near
the earth's surface or at high altitudes. The intense electric and magnetic
fields can damage unprotected electrical and electronic equipment over
a large area. See electromagnetic radiation, High-altitude burst.
Electromagnetic Radiation - A traveling wave motion resulting
from oscillating magnetic and electric fields. Familiar electromagnetic
radiations range from X rays (and gamma rays) of short wavelength (high
frequency), through the ultraviolet, visible, and infrared regions, to
radar and radio waves or relatively long wavelength (low frequency). All
electromagnetic radiations travel in a vacuum with the velocity of light.
Electron - A particle of very small mass, carrying a
unit negative or positive charge. Negative electrons, surrounding the
nucleus, (i.e., orbital electrons), are present in all atoms: their number
is equal to the number of positive charges (or protons) in the particular
nucleus. The term electron, where used alone, commonly refers to negative
electrons. A positive electron is usually called a positron, and a negative
electron is sometimes called a negatron. See Beta particle.
Electron Volt (EV) - The energy imparted to an electron
when it is moved through a potential difference of 1 volt. It is equivalent
to 1.6 x 1012 erg.
Element - One of the distinct, basic varieties of matter
occurring in nature which, individually or in combination, compose substances
of all kinds. Approximately ninety different elements are known to exist
in nature and several others, including plutonium, have been obtained
as a result of nuclear reactions with these elements.
EMP - See Electromagnetic pulse.
Energy absorption - See Absorption.
Energy Partition - The distribution of the total energy
released by a nuclear explosion among the various phenomena (e.g., nuclear
radiation, thermal radiation and blast). The exact distribution is a function
of time, explosion yield, and the medium in which the explosion occurs.
Expedient Shelters - Fallout shelters ( also known as
hasty shelters) offering reasonable radiation protection that
can be fashioned quickly in the event of nuclear attack. See also fallout
shelter and protection factor.
Exposure - A measure expressed in roentgens
of the ionization produced by gamma (or X) rays in air. The exposure
rate is the exposure per unit time (e.g,, roentgens per hour). See
Dose, Dose Rate, Roentgen.
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