RADIOACTIVITY IN THE SOUTHERN STRATOSPHERE 411 Table lL—SUMMARY OF 1961 AND 1962 ATMOSPHERIC TESTS Detonation Inclusive dates Mean date Fission Latitude for series yield, Mt 52°N, 7o°N Oct. 15, i961 17 U.S.S.R. Sept. 1—Nov. 4, 1961 U.S.S.R. Oct. 30 (~55 Mp) 75°N Oct. 15, 1961 8 United States July 9, 1962* 17°N July 1, 1962 i U.S.S.R. U.S.S.R. Aug. 5—Nov. 17, 1962 Dec. 18—Dec. 24, 1962 Oct. 15, 1962 Dec. 20, 1962 60 U.S.S.R. United States United States Oct. 23 (~25 Mt) Apr. 25—July 11, 1962 Oct. 2—Nov. 4, 1962 75°N 2°N L7°N 92°N, 7o°N 52°N, 75°N = > Oct. 15, 1962 *Starfish Prime detonation at 400 km. The 1961 U.S.S.R. test series has been subdivided into three components since data obtained at 31°N in 1962 suggests that each of these components may have followed significantly different distribution pat- terns. The altitude profiles for long-lived *°Sr concentrations, ®Zr (65day half-life)/**Sr, and *4Mn (310-day half-life)/*"Sr activity ratios are shown in Fig. 1 for February 1962 at31°N. Manganese-54 is a neutron- activation product rather than a fission product, and one may reasonably presume, therefore, that it was produced in largest quantities in the 55-Mt thermonuclear detonation of Oct. 30, 1961, in which the high- est neutron flux was produced. These data show that (1) a considerable fraction of new debris, indicated from high values for the ™Zr/*"Sr ratio, was present at 60,000, 90,000, and 105,000 ft but only traces at 70,000 and 80,000 ft; (2) the largest quantity of new debris was at 60,000 ft where both *zr/™Sr and total Sr were the greatest; (3) the new debris at 60,000 and 105,000 ft was low in “Mn, whereas that at 90,000 ft contained relatively large amounts of “Mn. The following hypotheses may be made to explain these observations: (1)debris from all the 1961 U.S.S.R. tests except the 25- and 55-Mt thermonuclear events stabilized below 70,000 ft; (2) fresh debris at 90,000 ft was due primarily to the 55-Mt device for which the activity ratio of “Mn/*°Sr at formation was about 100, a value determined from the observed Mn and a calculation for the new Sr based on the observed ™Zr and the expected ™Zr/*"Sr formation ratio; (3) fresh debris above 100,000 ft came from a shot other than the 55-Mt detonation (either from the 25-Mt shot or from one or more unannounced high-altitude detonations). If the 25-Mt device accounted for this new material, a large fraction of the debris from this shot may have been present above the maximum sampling altitude of 105,000 ft. Neutron-activation products other than "Mn, such as »Fe and 124Sb, were also found in the stratosphere after the 1961 U.S.S.R. test series.’ Additional quantities of these radionuclides, as well as ™y, were produced in the 1962 atmospheric tests,4 Their use as tracers for