PARTICLE ANALYSIS PROGRAM AT LRL
151
Fallout
A necessary input to meteorological models of the fallout process
is the distribution of the particulate material in terms of sedimentation
rate, i.e., what fraction can be treated as a stable aerosol and what
fractions will be deposited by sedimentation at various rates. Total
beta radiation, total gamma radiation, total mass, and individual radio-
nuclides may each be distributed differently in terms of sedimentation
rate. The analytical program is designed to provide information from
which the various distribution functions can be determined. If the samples from which the distribution functions are determined are representative of the true particle population, then the distribution functions
can be used to deduce the absolute amountof individual radionuclides
introduced into the various atmospheric reservoirs.
Particle Formation.
The size, the composition, and the radionuclide distributions of
particles produced by a specific nuclear shot depends upon the energy
output of the shot, the mass and the chemical composition of the va-
porized material, and the environment in which the shot occurs. In-
tercomparison of the distribution functions obtained from a series of
shots occurring in similar environments can in principle be used to
arrive at relations between parameters of the distribution functions
and those of energy, mass, and composition of the nuclear shot. Such
relations would permit the prediction of particle characteristics for
specific combinations of energy, mass, and composition. The manner
in which the distribution of individual radionuclides varies from element to element for a particular shot and from shot to shot as condensation conditions change should provide a valuable insight into the
thermodynamics of the condensation process.
Biological Availability
In general, each radionuclide will be distributed uniquely among
the particle classes, with the volatile elements tending to be concen-
trated in the finer particles and the more refractory elements being
concentrated in the coarser particles. Biological availability of a particular radionuclide may be assessed if both its distribution among the
particle groups and the chemical composition of the particles are
known. The’ data provided by the analytical program include a spectrum of radionuclides ranging from extremely volatile to extremely
refractory species.
Although the program at LRL is intended ultimately to include all
forms of man-made particulate radioactivity, the initial work has been