which case the mean and median are equal. The median therefore is used in
this study as an estimate of the mean, since it depends (at least in the
doubtful activity region) only on the number of particles. In addition
the median value is less distorted by the extreme values that occur in
some cases.
Only the field data (YAG-40-Shot A and YAG-40-Shot B) are considered
reliable for activity-size and activity distribution information. This
set of data shows that the activity range and median activity both increase
with particie size. The measurements made at NRDL are less useful, showing a high percentage of particles with very low or zero activities. These
particles were counted at late times, and their activities had decayed to
or past the limits of detection. In the case of zero activities the question of which of these decayed past detertion and which were originally
inactive cannot be resolved. It is noteworthy that all the YAG~40-Shot A
particles studied were active and 98% of the YAG-40-Shot B particles were
active.
Activity Distribution Studies
A preliminary study of the activity distribution within a size group
and a size-type subgroup was conducted with the field data. The study was
Limited to considering whether or not the distribution of activities
followed normal or log-normal distribution functions. A normal distribution tendency was exhibited only by the size-type subgroups containing 30
or more particles; as is shown by their data plotted on normal-probability
paper in Figs. 2 through 5. A distribution function could not be assigned
to the other groups.
The YAG-40-Shot B particles provide information on the distribution of
activity among size groups as well as the distribution of activity by
particle type within a size group.
detailed in Table 2.
The activities, listed in Table 1, are
Activity end Size Relationship
With the field data, median activities of size and size-type groups
were plotted against mean diameters to study the activity-size relationships and the influence of particle type in such relations. Figure 6
depicts the log-log plots of the YAG-40-Shot A particles and Fig. 7, the
YAG-40-Shot B groupe.
Shot A dendrite-like and Shot B spheroidal particles
were not studied typewise because their data were too sparse; however
they are included in the composite group studies. In each plot the locus
of points suggested a linear relationship; consequently regression lines
were fitted by means of a modified least squares method. In this method
the median activity of the group was weighted by the number of particles
in the group. For calculation, activities greater than 10 c/m were
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