A-Bomb - An abbreviation
for atomic bomb.See Nuclear weapon .
Absorbed Dose - The amount of energy imparted by nuclear (or
ionizing) radiation to unit mass of absorbing material. The unit is the
rad. See Dose, Rad.
Absorption - The irreversible conversion of the energy of an
electromagnetic wave into another form of energy as a result of its interaction
with matter. As applied to gamma (or X rays) it is the process (or processes)
resulting in the transfer of energy by the radiation through an absorbing
material through which it passes. In this sense, absorption involves the
photoelectric effect and pair production, but only part of the Compton
effect. See Attenuation, Compton effect, Pair production, Photoelectric
Absorption Coefficient- A number characterizing the extent to
which a specified gamma (or X) rays transfer their energy to a material
through which they pass. The linear energy absorption coefficient
is a measure of the energy transfer (or absorption) per unit thickness
of material and is stated in units of reciprocal length (or thickness).
The mass energy absorption coefficient is equal to the linear
absorption coefficient divided by the density of the absorbing material;
it is a measure of the energy absorption per unit mass. See Attenuation
Afterwinds - Wind currents set up in the vicinity of
a nuclear explosion directed towards the burst center, resulting from
the updraft accompanying the rise of the fireball.
Air Borne Radioactivity - Any radioactive material suspended
in the atmosphere.
Air Burst - A nuclear weapons explosion that occurs above the
ground surface, high enough so that the resulting fireball does not touch
the earth's surface when the luminosity is a maximum (in the second pulse)
or scoop out a crater. See also surface burst.
Air Sampler - A device used to collect a sample of the
radioactive particulates suspended in the air.
Alpha Particle - A particle emitted spontaneously from
unstable nuclei of some radioactive elements. It is identical with a helium
nucleus, having four mass units and an electric charge of two positive
units. Compared to other forms of radiation at the same energy, it does
not have much penetrating power. See Radioactivity.
Angstrom - A unit of length, represented by A, equal
to 10-8 centimeter. It is commonly used to express the wavelengths
of electromagnetic radiations in the visible, ultraviolet, and X-ray region.
Antiparticle - A particle that has the same mass as another
particle but has opposite values for its other properties; interaction
of a particle and its antiparticle results in annihilation and the production
of radiant energy.
Arching - In the case of a buried structure, it is the
tendency for the soil particles to lock together in the form of an arch,
with the result that part of the stress is transmitted around the structure
instead of through it.
Armed - The configuration of a nuclear weapon in which
a single signal initiates the action for a nuclear detonation.
Apparent Crater - See crater.
Atom - The smallest (or ultimate) particle of an element
that still retains the characteristics of that element. Every atom consists
of a positively charged central nucleus, which carries nearly all the
mass of the atom, surrounded by a number of negatively charged electrons.
so that the whole system is electrically neutral. See Electron, Element,
Atomic Bomb (or Weapon) - A term sometimes applied to
a nuclear weapon utilizing fission energy only. See Fission, Nuclear
Atomic Cloud - See Radioactive cloud.
Atomic Number - See Nucleus.
Atomic Weight - The relative mass of an atom of the given
element. As a basis of reference, the atomic weight of the common isotope
of carbon (carbon-12) is taken to be exactly 12.; the atomic weight of
hydrogen (the lightest element) is then 1.008. Hence, the atomic weight
of any element is approximately the mass of an atom of that element
relative to the mass of a hydrogen atom.
Attenuation - Decrease in intensity of a signal, beam
or wave as a result of absorption and scattering out of the path of a
detector, but not including the reduction due to geometric spreading (i.e.,
the inverse square of distance effect). As applied to gamma (and X) rays,
attenuation refers to the loss of photons (by the Compton, photoelectric,
and pair production effects) in the passage of radiation through a material.
See Absorption, Inverse square law, Photon, Scattering.
Attenuation Coefficient - A number characterizing the
extent of interactions of photons of specified gamma (or X) rays in their
passage through a material. The linear attenuation coefficient
is a measure of the photon interaction per unit thickness of material
and is stated in units of reciprocal length (or thickness). The mass
attenuation coefficient is equal to the linear attenuation coefficient
divided by the density of the material; it is a measure of the attenuation
per unit mass. See Absorption coefficient.
Background Radiation - Nuclear (or ionizing) radiations
arising from within the body and from the surroundings to which individuals
are always exposed. The main sources of background radiation are potassium-40
in the body, potassium-40 and thorium, uranium, and their decay products
(including radium) present in rocks and soil, and cosmic rays. Background
radiation due to cosmic rays and natural radioactivity is always present.
Base Surge - A cloud which rolls outward from the bottom
of the column produced by a subsurface explosion. For underwater bursts
the visible surge is, in effect, a cloud of liquid (water) droplets with
the property of flowing almost as if it were an homogeneous fluid. After
the water evaporates, an invisible base surge of small radioactive particles
may persist. For subsurface land bursts the surge is made up of small
solid particles but it still behaves like a fluid. A soft earth medium
favors base surf formation in and underground burst.
Bearing Wall - A wall which supports (or bears) part
of the mass of a structure such as the floor and roof systems.
Becquerel (Bq) - The unit of activity of a radionuclide,
equal to the activity of a quantity of a radionuclide having one spontaneous
nuclear transition per second.
Beta Particle - A charged particle of very small mass
emitted spontaneously from the nuclei of certain radioactive elements.
Most (if not all) of the direct fission products emit (negative) beta
particles. Physically, the beta particle is identical with an electron
moving at high velocity. Depending on its energy, it can penetrate body
tissue fairly deeply and cause substantial damage to internal organs and
tissue. See Electron, Fission products, Radioactivity.
Beta Patch - A region of air fluorescence formed by absorption
of beta particles from the fission products in the debris from a nuclear
explosion above about 40 miles altitude.
Biological Half-life - The time required for the amount
of a specified element which has entered the body (or a particular organ)
to be decreased to half of its initial value as a result of natural, biological
elimination processes. See Half-life.
Bioassay - The method(s) for determining the amount of
internal contamination received by an individual.
Black Body - An ideal body which would absorb all (and
reflect none) of the radiation falling upon it. The spectral energy distribution
of a black body is described by Planck's equation; the total rate of emission
of radiant energy is proportional to the fourth power of the absolute
temperature (Stefan-Boltzmann law).
Blast Loading - The loading (or force) of an object caused
by the air blast from an explosion striking and flowing around the object.
It is a combination of overpressure (or diffraction) and dynamic pressure
(or drag) loading. See Diffraction, Drag loading, Dynamic pressure,
Blast Scaling Laws - Formulas that permit the calculation
of the properties, e.g., overpresssure, dynamic pressure, time of arrival,
duration, etc. of a blast wave at any distance from an explosion of specified
energy from the known variation with distance of these properties for
a reference explosion of known energy (e.g., of 1 kiloton). See Cube
Blast Shelter - A structure, usually embedded in the
earth, designed to withstand the overpressures due to a nuclear blast;
specifically, a shelter that can withstand a 10 psi overpressure. The
"hardness" of a blast shelter refers to the level of overpressure
it can withstand.
Blast Wave - A pulse of air in which the pressure increases
sharply at the front, accompanied by winds, propagated from an explosion.
See Shock wave.
Blast Yield - The portion of the total energy of a nuclear
explosion that manifests itself as a blast (or shock) wave.
Bomb Debris - See Weapon debris.
Boosted Fission Weapon - A weapon in which neutrons produced
by thermonuclear reactions serve to enhance the fission process. The thermonuclear
energy represents only a small fraction of the total explosion energy.
See Fission, Thermonuclear.
Breakaway - The onset of a condition in which the shock
front (in the air), moves away from the exterior of the expanding fireball
produced by the explosion of a nuclear (or atomic) weapon. See Fireball,
Bremsstrahlung - Literally "braking radiation."
Radiations covering a range of wavelengths (and energies) in the X-ray
region resulting from the electrical interaction of fast (high energy)
electrons with atomic nuclei. Bremsstrahlung are produced by the interaction
of beta particles with matter. See X rays.
Burst - Explosion or detonation. See Air burst, High-altitude
burst, Surface burst, Underground burst, underwater burst.
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