410 SALTER INTRODUCTION The establishment of a balloon-sSampling station at Mildura, Australia, in early 1961 provided an opportunity for studies of nuclear debris in the stratosphere of the southern hemisphere in greater detail than during the period of weapons testing in the 1950’s, Some results for such debris from the 1961 and 1962 test series are discussed here, Data will be presented on the fraction of stratospheric *Sr at 34°S attributable to the 1961 U.S.S.R. series and to Starfish Prime,* the U. S. detonation of July 9, 1962, during Operation Dominic I at 400 km above Johnston Island at 17°N. The presence of debris from these detonations in the stratosphere of the southern hemisphere and its contribution to the total Sr are of considerable interest both for determining the transport mechanisms for radioactive materials injected into the atmosphere from a nuclear detonation or the burnup of a nuclear-powered satellite device and for predicting fallout patterns for such atmospheric contaminants. Mildura, Australia, at 34°S, is one of the two stations from which high-altitude samples have been collected on a regularbasis since 1961 under a program sponsored by the AEC. Balloon-borne filtering devices using IPC 1478 filter paper are operated under contract with the Department of Supply, Commonwealth of Australia. Duplicate samples have been collected monthly at 50,000, 60,000, 70,000, 80,000, and 90,000 ft from 1961 to mid-1962 and at 65,000, 80,000, 90,000, and 105,000 ft since mid-1962. A similar collection schedule has been carried out for the AEC by Detachment 1, 6th Weather Squadron, Good- fellow Air Force Base, San Angelo, Tex., at 31°N. The sampling pro- gram now includes sites at 9 and 65°N operated on an alternating basis. Filters are sent to the Health and Safety Laboratory (HASL) where gamma spectra are obtained. One sample from each pair collected is then radiochemically assayed for several fission products and other radionuclides produced by weapons testing. Most of the analyses on samples collected since early 1962 have been performed by Isotopes, Inc., Westwood, N. J. Results of total gamma activity measurements and radionuclide analyses are reported quarterly.!~4 1961 AND 1962 ATMOSPHERIC TESTS Between the resumption of weapons testing by the U.S.S.R. on Sept. 1, 1961, and the end of 1962, several nuclear test series in the atmosphere took place.*'® These are summarized in Table 1. The column headed “mean date for series’ in Table 1 is used as the mean formation time for the production of radionuclides for the series. *Starfish Prime is referred to as Starfish throughout.