STRATOSPHERIC RADIOACTIVITY IN THE SOUTHERN HEMISPHERE FROM 1961 AND 1962 WEAPON TESTS LEONARD P. SALTER Health and Safety Laboratory, U. 8. Atomic Energy Commission, New York, New York ABSTRACT An evaluation of data from air-filter samples collected between 60,000 and 105,000 ft at 34°S gives some indication of the sr concentrations for nuclear debris attributable to the 1961 U.S.S.R. test series and to Starfish Prime, the U. S. detonation at 400 km on July 9, 1962. Strontium-90 from the 1961 U.S.S.R. series was present in small amounts below 70,000 ft at 34°S throughout 1962 and may have been a significant component of the relatively large levels observed above 100,000 ft in late 1962 and early 1963. This material probably accounted for a major part of the fivefold increase in Sr concentration from April to June 1963 between 70,000 and 90,000 ft. We ascribe the 1961 debris above 70,000 ft to the approximately 25 Mt shot of the series. As deduced from measurements of 1080q, Starfish Prime debris first appeared within the range of the sampling program in December 1962 at 105,000 ft at 34°S. By mid-1964 it was present throughout the stratosphere of. both hemispheres. The distribution of this material appears similar to that from Orange, the high-altitude rocket shot of August 1958, The following movements broadly describe the dominant features of the distribution pattern: (1) rapid horizontal spreading at high altitudes, (2) subsidence into the polar stratosphere, and (3) movement in the stratosphere toward the equator in the hemispheric spring and summer. 409