VARIATION OF RADIOACTIVITY IN SURFACE AIR
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U.S.S.R. TESTS
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‘ouees SERRUCEUBERREUUSECREGESEEREREER SHORE SREEREGHEGUROCRUGHUUNEHOGRUGEEEEEEE
Jan.— Dec.
1959
Jan.— Dec.
1960
Jan.— Dec.
1961
Jan.— Dec.
1962
Jan.— Dec.
1963
Jan.— Dec.
1964
Fig. 1—1%"Cs, !"Rh, and 54Mn in surface air at Argonne, Ill.
each year. In 1961 the maximum was observed during May and June,
and in 1962 and 1963, during June and July. In 1964 the maximum occurred during late May and early June, as indicated in Fig. 1. Similar
observations have been made at other locations within the northern
hemisphere.>~>
During 1961 through mid-1964, an appreciable portion of the total
137Cg present in surface air was of high-altitude origin as inferred
from the measured concentrations of ‘"Rh and *Mn, which are also
illustrated in Fig. 1. The !"*Rh was produced for the most part as a
tracer in the Orange shot of the Operation Hardtack I test series on
Aug. 11, 1958, which had a burst height of about 43 km over Johnston
Island.® The concentrations of '*Rh have been corrected for radioactive
decay to that date. Manganese-54 was produced inhigh-yield shots dur-
ing the Soviet 1961 test series, and there are indications from the Ash
Can balloon flights made at San Angelo, Tex.,’:® that “Mn was also pro-
duced during high-yield and/or high-altitude shots during 1962. The
*4Min values shown in Fig. 1 have been corrected for radioactive decay
to mid-October 1961. Thus both !°*Rh and *4Mn may be reasonably used
as tracers for high-altitude debris. As seen in Fig. 1, '*Rh reached a