RADIOACTIVITY IN THE SOUTHERN STRATOSPHERE 413 1962 AND 1963 STRATOSPHERIC ACTIVITY AT 34°S To some extent the levels of nuclear debris at 34°S maybe followed by measurements of total gamma activity. Theseare particularly useful in defining incursions of new debris or other changes in the regime of material, especially when the "Sr concentrations are only slightly affected. Figure 2 shows the gammaactivity concentrations at 34°S since 1962. From these data the following increasingactivity trends appear to be the most significant at 34°S in 1962 and 1963: 65,000 ft from July to September 1962, 80,000ft from August to November 1962, 105,000 ft in December 1962, 90,000 ft from December 1962 to June 1963, 80,000 ft from April to June 1963, and 65,000 ft in September 1963. A study of the fission-product radionuclides '*°Ba (12.8-day half- life), Zr (65-day half-life), ‘““Ce (285-day half-life), and “Sr (27.7- year half-life), as well as the cadmium isotopes and 54Min, permits some evaluation of the origin of debris that accounts for these increases. Published radiochemical data*®* corrected for laboratory bias were used for this study. These were augmented by radiochemical re- sults for '%cqa and '3™Cd obtained at HASL and spectral analysis for 14039, ®zr, and Mn. The fission-product results are used in equations of the following general form to calculate values for A,, the activity concentration on the sample-colliection date of nuclide A produced in the nth test series: A tot = 2) An B, an . Ze —(Ap-A aT n where A,,, = total activity concentration of A on the collection date Z =formation activity ratio of fission product B to fission product A Ag and A, = decay constants of fission products B and A, respectively T, =time elapsed between the series formation date and the , sample collection date The values of T, are calculated from the “mean date for series” given in Table 1. The formation-activity-ratio values, Z, are calculated from data on fission yields for a typical thermonuclear device.’ They are given in Table 2 with the ratio half-lives. In weaponstests, however, fission yields and, therefore, activity ratios vary significantly depending on the energy spectrum of prompt neutrons emitted and the fissionable materials present. The use of a single-valued constant determined from a typical device for the average formation ratio for all series may introduce a considerable error into the evaluation.