oD ——— Various amounts of 285-day Cel. Pr!*, 1-year Rul?6_ Ryle 27-year Cs!37_2.6 m Ba!9’, and 65- day Zr??- Nb% are present on the filters. The 65-day Zr™-Nb” completely masks the presence of the Cs!3? on all filters collected since August, 1956. The amounts of Cs present on these latter papers have not been determined to date, although the spectra will be peeled apart when time permits. Unfortunately, all papers collected prior to March, 1953, except for the month of June, 1952, are missing. The amount of Cs!37 per paper, expressed in arbitrary units, is given by the upper curve of Fig. 19. 30- o Qo 20+ ° 2 3 s IS~ s o aa 10 | a "\ 50 \ On 4 ° geo P [ 1\Q 5+ | | id t average Vad j of 3 subjects | e x 40 a 20 8 o of & 30% io “ ; a > i® “ ¥--SUATERUE RERENEDUETCHCUTRERTDEEDE CUDEETUFURSEEDUUEUEUTES "53 «| Fig. 19. 6°540—CUdL 55 UL 5G 4 CLOT Cs)" activity in filter ‘papers The Cs!37 atmospheric contents as shown by Fig. 19, increased by a factor of about 6 in the spring of 1953 and remained at this higher level until January 1955, except for an upward excursion immediately following Operation Castle, March 1954. It is of decided interest that the atmos- pheric Cs!37 content, at Chicago at least, did return to its 1953 value in the latter part of 1954. The 1955 excursion is due to the 14 U.S.A. con- tinental tests (Operation Teapot) and the early 1956 excursion is probably due to a combination of the American tests in the Pacific and the Russian tests. The various Russian, English, and American tests have taken place with such regularity since 1955 that the Cs atmospheric content has not returned to its 1953-1954 plateau value. The Cs present on the papers collected since August 1956 is completely masked by Zr”-Nb” from Russian tests during the last half of 1956; efforts will be made to measure it by nondestructive tests. 5012132 : + : re & ca -