RADIOACTIVITY IN THE SOUTHERN STRATOSPHERE 415 Table 2— FORMATION ACTIVITY RATIOS FOR FISSION PRODUCTS FROM A TYPICAL THERMONUCLEAR DEVICE Nuclide ratio, B/A 10R9/57r 8Sr/57Zr Hy/57r 57r/4Ce 14ce/Msr BICs/MSr Formation activity ratio, Z 5.2 0.65 Ratio half-life, days [In 2/(Agp—Aa)] 15.9 227 0.82 4,7 639 84 1.45 ~105 48 293 CONTRIBUTIONS FROM THE 1961 U.S.S.R. TESTS The concentration profiles for total *“Sr at 34°S are given in the second column of Table 3 for several periods in 1962 and 1963. The calculated fractions attributable to the 1961 U.S.S.R. test series are given in the third column. The results indicate that 1961 debris was present in the lower stratosphere in the first half of 1962, accounting for a few percent of the total “Sr. It was undetectable above 70,000 ft although a few high, but suspect, '‘ce/*Sr values suggest that traces might have been present at 105,000 ft. The fresh debris accounting for increased gamma activity concentrations at 65,000 and 80,000 ft in August and September was due to the Dominic I series, April through July 1962, that in- creased the “sr levels just slightly above that attributable to pre-1961 debris. Only for the latter part of the year at 65,000 and 105,000 ft is it possible to assign more than 10% of the Sr to the 1961 tests, as may be seen from the December data. Although the higher gammaactivity concentration at 105,000 ft may in part be explained as being attributed to the 1961 debris, the larger fraction of postmoratorium material at this latitude came from 1962 tests. Additional Sr from 1961 tests at the high altitudes sampled is suggested by the April 1963 data. However, it was in June at 77,000 and 86,000 ft, when the gamma activity concentrations were at their peak and the total ®°Sr had increased by a factor of 5 over April levels, that the largest amounts of 1961 debris appeared to be present: up to 500 dis/min per 10° scf. Conclusions about these levels of 1961 U.S.S.R. debris must be reserved until evidence that the fission-product formation ratios for a typical device which were used in the calculations approximate the average for weapons detonated in 1961 and 1962. If, for instance, the average ‘“4ce/*"Sr ratio for Dominic I was 40 instead of 48, it is pos-