exposure.
A measure expressed in roentgens of the ionization produced by gamma rays (ar X-rays) in arr.
he exposure rate
roentgen.
15
the exposure per unit
time
(e.g.,
raentgens per hour).
exposure rate contours.
Lines joining points which have the same radiation
out pattern, represented in terms of roentgens per hour.
FSU.
See dose,
dose rate,
intensity that define a
fali-
A single-engine Navy fighter developed by Vought-Sikorsxy and Chance Vought. Six F4U5N models were
used in CASTLE as a fighter element. An additional four earlier models scheduled for salvage were
used for unmanned fallout experiments in CASTLE Project 6.4.
F-84G.
Single-engine jet fighter developed by Republic Aircraft and used from [VY (1952} through REOWING
(1956) as cloud sampler aircraft.
F8-36.
Featherweight 8-36 bomber; t.e., a 8-36 bomber stripped of equipment (such as armament} to increase its performance in a noncombat mode.
Fallout.
The process or phenomenon of the descent to the Earth's surface of particles contaminated with
radioactive material from the radioactive cloud. The term is also applied in a collective sense to
the contaminated particulate matter itself.
The early (or local) fallout is defined, somewhat arbi-
NORAaR
trarily, as particles reaching the Earth within 24 hours after a nuclear explosion. The delayed {or
worldwide} fallout consists of the smaller particles, which ascend into the upper troposphere and
stratosphere and are carried by winds to all parts of the Eartn.
The delayed fallout is brought to
Earth, mainly by rain and snow, over extended periods ranging from months to years.
fathometer. A depth-sounding instrument.
The depth of water is measured by noting the time the echo of a
sound takes to return from the bottom.
film badges. Used for
pieces of film of
rial) that blocks
degree of fogging
absorbed dase is calculated.
eu Tp ee
fireball.
SRS pinata 4
the indirect measurement of ionizing radiation. Generally contain two or three
different radiation sensitivities. They are wrapped in paper (or other thin matelight but is readily penetrated by gamma rays.
The fiims are developed and the
(or blackening) observed 15 a measure of the gamma-ray exposure, from which the
Film badges can also measure beta and neutron radiation.
The luminous sphere of hot gases that forms a few millionths of a second after a nuclear explo-
ston as the result of the absorption by the surrounding medium of the thermal X-rays emitted by the
extremely hot (several tens of millions of degrees) device residues.
The exterior of the fireball in
air is initially sharply defined by the luminous shock front and later by the limits of the hot gases
themselves.
fission. The process of the nucleus of a particular heavy element splitting inta two nuclei of lighter
elements, with the release of substantial amounts of energy.
The most important fissionable materials
are uranium-235 and plutonium-239; fission is caused by the absorption of neutrons.
fission detectors. Radiation pulse detector of the proportional counter type in which a foil or film of
fissionable materials is incorporated to make it respond to neutrons.
Fission products. A general term for the complex mixture of substances produced as a result of nuclear
fission.
A distinction should be made between these and the direct fission products or fission fragments that are formed by the actual splitting of the heavy-element nucie: into nuclei of medium atomic
weight. Approximately 80 different fission fragments result from roughly 40 different modes of fission of a given nuclear species (e.g., uranium-235 or plutonium-239).
The fission fragments, being
radioactive, immediately begin to decay, forming additional (daughter) products, with the result that
the complex mixture of fission products sa formed contains over 300 different radionuclides of 36
elements.
fixed alpha.
Alpha ragioactivity that cannot be easily removed as evidenced by no measured change in a
swipe of a 100-cm¢
fluorescence.
area.
The emission of light (electromagnetic radiation) by a material as a result of the absorp-
tion of energy from radiation.
sion process.
FOPU.
The term may refer to the radiation emitted, as well as to the emis-
Fallout Prediction Unit.
forward area.
The PPG and adjoining areas (e.g., Kwajalein).
fusion.
The combination of two Tight nuctei to form a heavier nucleus, with the release of the difference
of the nuclear binding energy of the fusion products and the sum of the binding energies of the two
light nuclei.
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