(C) Evidence for High Stratosphere Holdup of Nuclear Bomb Debris E. A, Martell Air Force Cambridge Research Laboratories Introduction It is the purpose of this symposium to explore the need for and the possible methods of sampling the high atmosphere, It is the object of this paper to review someof the evidence for possible substantial high strato- sphere retention of radioactive contamination from past nuclear tests. During and following the November 1952 Ivy and spring 1954 Castle tests of multimegaton thermonuclear devices at the Pacific Proving Grounds, there existed no adequate stratospheric sampling techniques that could be employed to assess the distribution and inventory of stratospheric contamination, The fraction of total bomb debris retained in the stratosphere was estimated as the difference between total production and the fraction deposited as local fallout. Estimates made on this basis suffer from the inherent difficulties of integrating local fallout over tens of thousands of square miles of ocean area, Estimates for the stratospheric fraction for high yield surface water shots range from 80 percent! to 30 percent, 2,3 The difference reflects uncertainties in estimation as well as possible influence of total energy-yield differences for the several events on which the estimates were based, Thus the stratospheric inventory for past high-yield surface detonations, which make up a substantial fraction of total test production, is at best quite poorly known, The integration of bomb debris deposited in world-wide fallout, based on radioassay of rainfall, soil and seawater samples, places further limits on the stratospheric inventory. However the complexity of the fallout pattern, the question of representativeness of samples, and the limited amount of good data for remote locations and ocean areas restrict the accuracy of cumulative world-wide fallout estimates, Thus material balance estimates of the residual contamination of the stratosphere, total fallout production less local fallout and cumulative world-wide fallout, are very uncertain, The present burden of long-lived fission products in the stratosphere above 100,000 feet lies somewhere between an appreciable fraction of total past production and a lower limit of nearly the total production of the Teak and Orange shots, two megaton yield nuclear detonations at high altitudes over Johnston Island. 4 Estimates of the high stratosphere content of residual contamination on the basis of fallout observations in the lower atmosphere are clearly unacceptable. Changes in the lower atmosphere fallout concentration and isotopic composition with time would provide a useful index of the atmospheric burden only if the stratosphere were well mixed. There is a mounting volume of evidence that the stratospheric residence time of nuclear . . . aL tt gs . . 5-7 . debris clouds varies widely with injection altitude and latitude >" and that the stratosphere is not well . 7,8 mixed. The question of the burden, distribution and mixing history of nuclear debris at levels above 100, 000 feet is one of the more important and interesting unsolved geophysical problems on world-wide fallout. Its