182 DREVINSKY AND PECCI In this paper we have presented our basic data. Further study is necessary for a better understanding of the worldwide stratospheric radioactivity relation with particle size. A more detailed analysis of these data from the viewpoint of aerosol dynamics is required. A sampler that would provide larger volume collections with emphasis on obtaining increased resolution within the size range r< 0.15 yu and operate reliably, especially at altitudes higher than 30 km, would contribute immeasurably to this study. ACKNOWLEDGMENTS We are grateful to Miss Anahid Thomasian for the radiochemical analysis of ‘4vin and J. V. Nikula for all gamma-activity measurements. Thanks are due to M. I. Kalkstein for helpful discussions. REFERENCES 1. J. Baumstark, L. Graf, I. Hall, 8S. Jones, J. Nash, R. Olson, S. Stern, L. Torgeson, and W. Zeller, Upper Atmosphere Monitoring Program, Report No. 2039, General Mills, Inc., June 1, 1960; and R. C. Wood et al., Upper Atmosphere Monitoring Program, Report No. 2109, Generali Mills, Inc., Sept. 15, 1960, 2. P. J. Drevinsky and E. A. Martell, Preliminary Results on the Size and Vertical Distributions of Residual Nuclear Debris in the Stratosphere, in Radioactive Fallout from Nuclear Weapons Tests, A. W. Klement, Jr.(Ed.), USAEC Report TID-7632, pp. 170-187, February 1962. 3. H. W. Zeller, Balloon-borne Particulate Fractionator, Report No. 1922, Final Report, General Mills, Inc., Feb. 1, 1960. 4, M. 1. Kalkstein, P. J. Drevinsky, E. A. Martell, C. W. Chagnon, J. E. Manson, and C, E. Junge, Natural Aerosols and Nuclear Debris Studies, Report AFCRC-TN-59-627, Air Force Cambridge Research Center, November 1959. 5. C, W, Chagnon and C. E. Junge, The Vertical Distribution of Sub-micron Particles in the Stratosphere, J. Meteorol., 18: 746-752 (1961). 6. E. A. Martell, The Chicago Sunshine Method, USAEC Report AECU-3262, Enrico Fermi Institute for Nuclear Studies, University of Chicago, May 1956. 7. W. F. Libby, Absolute Assay of Beta Radioactivity in Thick Solids, Anal. Chem., 27: 921-927 (1955); and Simple Absolute Measurement Technique for Beta Radioactivity, Anal. Chem., 29: 1566-1570 (1957). 8. U. S. Weather Bureau, Announced Nuclear Detonations 1945-1962, in Fallout Program, Quarterly Summary Report, USAEC Report HASL-142, pp. 218-239, Health and Safety Laboratory, Jan. 1, 1964. 9. C. E, Junge, C. W. Chagnon, and J. E. Manson, A World-wide Stratospheric Aerosol Layer, Science, 133: 1478-1479 (1961); and C. E, Junge and J. E. Manson, Stratospheric Aerosol Studies, J. Geophys. Research, 66: 2163- 2182 (1961), 10. L. P. Salter, High Altitude Balloon Sampling Program, in Fallout Program, Quarterly Summary Report, USAEC Report HASL-140, pp, 166-214, Oct. 1, 1963, and USAEC Report HASL-144, pp. 184-219, Apr. 1, 1964, Health and Safety Laboratory. 11, S. Katcoff, Fission-product Yields from U, Th, and Pu, Nucleonics, 16(4): 78-85 (1958).