INTRODUCTION
Relationships between the size and radioactivity of fallout particles play an important role in fallout phenomenology and model research.
These relationships aid in the assessment of radiological situations and,
more important, may reveal the manner in which activity is associated
with the particles. Furthermore, the modes of association may provide
some insight into the history of fallout material and suggest the mechan-
ism of particle formation and contamination.
It has been generally hypothesized that activity is a function of
either particle surface area or volume.
Experimental data to confirm
this hypothesis is needed. In the case of coral fallout particles, radioautographic studies by Adamsl-4 have shown the existence of three general
types of particles with intrinsic differences in activity association.
Irregularly shaped particles generally have the activity concentrated on
the exterior, indicating that it was deposited after the particle was
formed. Spheroidal particles usually have the activity dispersed throughout, suggesting that it was incorporated during some molten state.
Regard-
ing the third type, particles with a dendrite-like structure, little is
known of activity association. The existence of such differences neces~
sitates the consideration of particile shape in the activity-size relationships of coral particles.
Other studies5»® have been limited to the composite activity associated with size fraction. However, certain deficiencies are inherent in
this method of study. The approach does not take into account the variability of particle activity due to particle type. Moreover, particle size
separation was generally accomplished by sedimentation, sieving and other
egitating methods; since a substantial portion of coral particles are
dendrite-like and fragile, these methods very likely cause particle breakup and subsequent errors. Regarded as smaller particles, the fragments
cause inaccuracies in the data, particularly fragments from particles with
activity concentrated on the exterior. It is essential, therefore, to
employ a method of study that will consider particle type and will not
break up fragile particles.
Such requirements are met by the study of individual discrete particles.* This approach not only provides reliable data but also gives needed
*
%It is to be noted that Kikuchi, et. al. at examined a number of individual CASTLE particles, but neglected particle type; no correlation
between size and activity was found.
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