FILTER PACK TECHNIQUE FOR CLASSIFYING RADIOACTIVE AEROSOLS BY PARTICLE SIZE. PART 3. THE SIZE DISTRIBUTION OF AIRBORNE FISSION PRODUCTS DURING 1963 AND 1964.
NAVAL RESEARCH LAB WASHINGTON D C
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Some 60-odd collections of radioactive particulate matter dispersed in the atmosphere were during the past two years by use of a filter pack technique utilizing four superimposed filters. The distribution of radioactivity among the filters was analyzed mathematically by means of four simultaneous linear algebraic equations which relate the particle size of the retained material to the filter characteristics so as to permit the assignment of radioactivity in each collection to four major size groupings 1.1 micron, 0.6 micron, 0.3 micron, and 0.15 micron particle diameter. A comparison of the relative amounts of various long-lived fission products Ce144, Pm147, Sr90, Cs137 and of the natural isotope RaD Pb210 in month-long collections by four-filter packs shows no significant evidence of fractionation effects among the long-lived fission products. This confirms the importance of the attachment process to the size of radioactive fission product conglomerates detected at ground level. Fresh debris from the Chinese nuclear test, however, exhibited a different isotopic distribution with size than did the older bomb debris. Proportionately more of the shorter-lived radioactive fission products collected during transit of debris from the Chinese test appeared in the largest particle size grouping.