NONTECHNICAL SUMMARY
The Problem
In order to predict the radiation hazards arising from fallout and
devise protective countermeasures against them it is necessary to determine the characteristics of the fallout particles. Among the important
characteristics needed is the relationship between two important individual aspects of fallout particles, size and radioactivity.
Previous studies have considered the total radioactivity associated
with particles grouped according to size ranges. However, this approach
does not consider the variation of radioactivity with particles of different shape, shape being an indication of the differences in the manner
radioactivity is incorporated in the particle. Also, the methods used
in past studies for separating the particles into size ranges did not
prevent the break-up of some particles, of which the fragments were
regarded as being smaller particles. These two conditions caused misleading results in the final data in attempts to quantitatively describe
& relationship between the size and radioactivity of fallout particles.
The Findings
In this investigation, the shape, size, and level of radioactivity
were determined for individual fallout particles. A wide range of radioactivity intensities was associated with each of the size groups and sizeshape groups of particles. In the case of particles collected at one station in the field, a possibility was indicated that the radioactivity is
normally distributed over a size-shape group. This set of data also indicate that regarding a relationship to particle shape, radioactivity varies
approximately as the square of the diameter for irregular particles and as
the 3.7 exponential power of the diameter for spheroidal particles. In
the case of dendrite~like particles, the activity varies with a function
exponentially greater than the irregular particle Punction.
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