fables 3.1 through 3.4 summarize the data on residual station locations,
time of arrival of fallout, maximm observed exposure rate, total exposure,
and @ecay exponent.
he averages decay exponent was found to be 1.1 for
Shots Zuni and Sew, 1.3 for Shot Navajo, and 1.2 for Shot Fistheed
(neglecting the results from Station 221.0hC, which received too little
exposure for accurate evaluation).
In the many cases where there vas
early rain leaching, the slope indicated by the data points taken after
rein had ceased was used to help determine the best-fit straight line.
Pigures 3.14 and 3.15 are typical curves showing the gamua-exposure-rate
change caused by rainfall.
In tuese curves, the gamas-exposure rate
after rainfall was approximately half of that expected if the normal
reticective decay were the only cause of change of exposure rate.
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In Figures 3.3 and 3.16, the buildup of the exposure rate is
:
apparently more complex tna: the monotonic buildup presented by most of
the other figures.
It appears that fallout ceased to arrive for e short
period at 60 minutes in Figure 3.15 and then commenced to arrive agein.
Giope changes are evident in the curves in Figures 3.9 and 3.10
after about plus 500 minutes.
This effect is probably not due to
instrumentation errore, because these curves represent the data from two
independent instruments located at the same station.
A possible explanation
of theee slope changes is the presence of one (or more tha one) redioactive
isotope whose half-life is such that the decay is slower than the coubined
fiss‘on fragment decay of T7)*?, and the decay elope is dominated by this
isotope frou about plus 500 minutcs until the end of the record.
However,
the instrumentation 414 not record for a sufficiently long time to determine
Gefinitively the half-life of this isotope.
ST, LOVIB KKe