156
RADIATION STANDARDS, INCLUDING FALLOUT
Experimental data on the third case—namely, that from Orange and Teak—
are somewhat sparse. The most striking feature is that debris from this source,
as indicated by Rh'”, did not appear in detectible quantity at ground level until
a year after detonation (in September 1959 Rh’ was first noted in surface air
at Argonne). Hence there is no dose contribution during the first year, and the
dose from short-lived fission products is severely reduced due to decay. Again
an equal partition between hemispheres was assumed. The 30- and 70-year
integral doses computed for these shots are shown in table I, and dose ratios
are indicated in table II.
The ratio of short-lived dose to Cs*” dose as well as the assumed deposition
of Cs” in terms of millicuries per square mile per megaton may be used to
evaluate the possible radiological implications of the Soviet 1961 polar tests
and those being conducted by the United States in the equatorial Pacific.
Only for the Soviet 1961 tests are sufficient data available to compare with
the situation observed in 1958-59. The simplest approach is to assume a direct
correspondence between events in 1958-59 and those occurring, and to occur,
in 1961-62. This is not a bad first approximation, since both series were conducted north of the Arctic Circle during the autumn. On two occasions in 1961,
however, very large detonations were involved, 25 megatons in one case and
57 megatons in the other, which resulted in sizable portions of the debris being
earried initially to greater altitude than was the case in 1958. Proceeding with
a direct comparison, and taking the figure of 25 megatons as thefission yield
of the 1961 series, one arrives at the dose from Cs™ and from short-lived activity
as indicated in table III. As of mid-May 1962 the integral dose from September
1961 from Soviet debris, including Cs��, as measured at Argonne is less than
50 percent of that observed during the corresponding period in 1958-59 due to
Soviet tests. The difference in deposition is perhaps illustrated more clearly
by comparing monthly deposition of Cs” as shown in table IV, where the present values are roughly one-half those attributed to 12.5 megatons in 1958-59.
The most ready explanation for this difference is that an appreciable fraction of the total yield is being held at high altitude or otherwise has not yet
been deposited. That holdup at high altitude is occurring was shown by a series
of balloon flights made during early April 1962 at Thule, Greenland, by a team
composed of Argonne and Weather Bureau personnel in which a gamma ray spectrometer was flown to altitudes of 100,000 feet. The results show considerable
debris above 75,000 feet, with the maximum concentration between 60,000 and
70,000 feet. Thus the behavior of a portion at least of the Soviet 1961 activity
may more closely resemble that from a high-altitude detonation than from an
injection into the low polar stratosphere. The rate of deposition should then
be slower, and the total dose will be reduced below that tabulated in table III.
In summary, the dose from short-lived fission products relative to that from
Cs’is greatest in the case of polar, low stratospheric injection.
The deposi-
tion of Cs™ per megaton of fission is also greatest in this case. The dose from
short-lived nuclides is somewhat less, relative to the Cs*” dose, in the case of
equatorial low stratospheric injection; the Cs™ deposition per square mile per
megaton of fission is also less (by a factor of 2), but is more widespread. Highaltitude detonations—presumably independent of latitude—result in an appre
ciable reduction in the dose from short-lived emitters, the bulk of which may
not survive the fairly long residence in the stratosphere. In addition decay of
longer-lived components may also become appreciable, and likewise result in
a reduced dose per megaton of fission. (This work was performed under the
auspices of the U.S. Atomic Energy Commission.)
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