Fizure 7 shows the ballesu Onli fse-99 Guta ug @ funetion of ic 1titude.
Only those samples with more Sr-90 than 10 dpm per
avoid spurious values.
1000 scf were used to
invalved in the radiochem-
The ceveral laboratories
ical analysis program are differentiuted by symbols.
The results show that
there is a tendency for the ratio to increase with altitude, althcugh the
variability is large.
The data are summarized in Table 4, together with the
(Certain doubtful values huve been excluded
data from the other investigators.
in the U.K. rainfall results.)
Table
Summary of Cs-137/Sr-90 Data
No.
Cases
Mean
Standard
Deviation
Balloon filters:
50,000 feet
13
2.11
1.11
65,000 feet
48
“2,80
1.31
80,000 feet
26
3.40
1.45
15
3.53
1.99
59
2.20
0.73
90,000 feet
--
NRL surface air filters
U. K. rainfall
122
1.63
0.63
AS can be seen from the last column of Table 4, the standard deviation
of the Cs-137/Sr-90 ratio from the balloon filters is two to three times greater
than found b,; other investigators.
This may be a result of radiochemical
procedures and is undoubtedly a function of the extremely minute amounts of
material collected during the flights.
NAS
The relatively short-lived isotopes, Ba~lk0O,
Zr-95 and Sr-89, can reveal
information on the age and origin of the activity sampled, particularly if the
debris is fresh, but the great variability found in these isotoves has made
interpretation difficult.
This variability may be real, reflecting the patchy
nature of fresh debris.
Cerium-144 tended to show more meaningful patterns than the shorter-lived
isotopes.
It has a half-life of 275 days (0.75 yr) and a fission yield about
25% greater than that of Sr-90.
Jf it can be assumed that fractionation is
unimportant and the collection efficiency of the filter for the two isotopes
is about equal, the Ce-l4h4/Sr-90 ratio can be useful in distinguishing between
sources of debris of different ages.
In the first half of 1957, the ratio for
Castle debris should be about 3 or i, while Redwing debris would have a value
it
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“eA ONAL AC. EMY UF SCIENCES
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