The age of fallout ©):
22 crs. uch im tn ways, one from the
sr&9/90 ratio, which varies as e functicn of time efter burst, and the
ae
other from percent contribtutisn of eet? be total ( activitye
The
theoretical sr&9/50 ratios usec te calculate burst cates were cbtained
from the Hunter and Ballou
yielc dats for these isctopes and their most
recently reported half-life vaelus:.:
The expected percent $r90
total 6 activity as a funetion <:f ti: i was obtained in the same waye
The approximate burst times have besn calculated fer all the data, and
the average burst months for each montn's samples, as obtained by both
methods are listed in Table 3,
Estimated burst dates of fallout in rain water.
Burst month calculated
from average Sr°9/30 ratios
Burst month calculated
from average % Sr70
March
September
4j007
March
195,
April
Auguet
toe,
November
195,
May
Geptenver
Llp.
November
1951
June
Ostober
Too!
February
1954
July
February
125%
October
195)
been
Sampling
Month
ee hemes eine an thd
Table 4.
ee te he in
is high, indicating old debris,
‘e’> contribution to total 6 activity
ra
From this it can be seen that the
AL tbe some time, the sr°9/o0 ratio is
This is possibly
due to enrichment of the Sr99 in fellout
in a mixture
ce
large enough for a mush late; iurct i.ts te be realized.
hat would occur
of material from different test ser.-..
.
Therefore,
BO 4.
the Ero?’ > vr >
>
the age of fallout anc can ke sens: 2)
:
is
,
o 4g
ls more sensitive indicator of
1. vield a rore valid estimation
1
q
x
“SNS
=
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AQE SS «
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~
%2
TO
g
-~
Se
ye
.
a
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a
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4
=
me
-
oh
se tae
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as % LamRNA
8OO em
Ty
~~eS ow
me
mq
Se Sa SS 5,
~
-
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-
om*
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A