562
HALL
rainfall-sample cross sections are similar in that at these stations
the beta~concentration minimums were not coincident with the rainfallrate maximums, At station 9 the cell crossed during a minimum in the
maximum intensity. Figure 37 shows that with the relatively moderate rainfall at that station, four samples were collected during the
sustained 20-min maximum, These four samples indicate a betaconcentration profile similar to that shown in Fig. 34 for station 3
during its stronger sustained maximum, At both stations the concentration associated with the minimums for the stations, along with
the ratio of particulate to dissolved beta activity, was at a peak in the
second of the four samples.
RESULTS
Comparison of Tables
1 and 3 with the radiochemical analysis
results obtained’ during the storms in the spring of 1963 show that
the beta concentration in the precipitation samples had decreased by a
power of 10. Such a decrease is expected because of decay and fallout
in the interim, although we are not sure that the degree of decrease is
consistent with other observations. The results discussed here of
storms of different sizes and intensities show that the ones of April 17
and April 23 had the higher values of average total beta concentration,
with the highest concentrations occurring at the stations that collected
peripheral rainfall. In the storms of May 9 and May 10, which were
larger storms and from which more samples per station were obtained,
the maximum concentration occurred at the station that had the least
total rainfall.
Of the 18 rainfall-sample cross sections presented, 15 hada
decrease in beta concentration from the first to the second sample with
14 of these inversely related to the rainfall rate. Only six of the sample
cross sections had the ratios of particulate to dissolved beta activity
of the initial and second samples in phase and decreasing with those of
the total beta concentration. The decreases in the ratios corresponded
to decreases in particulate beta concentrations. In 12 of the 18 cross
sections, there was a peak in the ratios associated with the rainfallrate maximums,
The beta concentration and the rainfall-rate profiles fit the
classifications as discussed by Huff.? Of the 18 beta-concentration
profiles, eight had beta maximums associated with the leading edge of
the storm, with five having a secondary maximum associated with the
rainfall-rate maximum. There were two profiles that had their maxi-
mum beta concentrations near the rainfall-rate maximums with the
secondary maximum associated with the leading edge of the storm.
In five profiles the beta concentration decreased from theinitial
sample to a minimum, which in three of the cases was associated with