510
HUFF
SPRINGFIELD
a
MILES
0 10 20 30
wit
Nn
512
Q\<
—1O
32
Fig. 2—-Sampling networks in 1963.
matic rainwater samplers used in conjunction with a special sampling
program, and the inner region is the East Central Illinois network.
Also, at each of the stations shown in Fig. 2, polyethylene collectors
were used to obtain samples of the total storm rainfall for the studies
discussed in this paper. A recording rain gauge was located at each of
the rainwater sampling stations. Through use of the networks shown
in Figs. 1 and 2, data were collected on areas of 10 to 6000 square
miles in the two-year sampling period, 1962 and 1963. Data collection
was continued on the East Central Illinois network in 1964.
Measurements of gross beta radioactivity were made with proportional counters. These instruments employ 27 geometry and are
provided with lead shielding such that the beta background does not
exceed 50 counts/min. Preparation of the samples for counting radio-
activity was done by using the method described by Weatherford,’ in
which the water sample is divided into suspended and dissolved solids
and eventually reduced to dryness on planchets. Repetitive counts
were made with each sample until consecutive concentrations agreed
within one Poisson standard deviation of the counting error for the
sample. This error was usually less than 5% for the 1962 and 1963
data. All samples were allowed to sit for 10 days or longer before
counting to minimize the effects of natural surface radionuclides such
as radon, and counts for a specific storm on a specific network were
made on the same day or on consecutive days to minimize uncertainty
in the calculations that might arise from the progressive decay of the
beta samples.