DOC Shed 4 Garele, ar CIE Cas Vaged ad #4 p¢Bo0¢ Long Term Activity Estimates For The Northern Marshall Islands This paper provides preliminary upper-bound estimates of the residual gamma activity on the northern Marsha}] Islends due to U.S. atmospheric testing at Bikini. These estimates are intended to be indicative of the activity to be determined by up-comino detziled surveys. Estimates are also provided for islands in the Enewetak atol} and compared with the 1972 survey. Finally, an analysis of wind pro- files and fallout patterns is presented which serves to delineate those northern Harshal] islands which were uncontaminated by fallout fron the Bikini tests. 4. _ APPROACH % After 20 years or so, the principal fission procucts of interest are 5720 and cls? whose characteristics are summarized belov. Isotope sree csi3/ Curies/kt of Fission at H+] Fraction of Total Curies 110 320 2.1x107? 61x10"? Half Life Decay Mode 20y 30y 3 only (100%) and y (93%) _ the fractional contribution of Cs 137 to the one-hour dose rate is not the same as the fraction of total Curies at one hour since the cs}? y energy 1s lower than that average energy for all fission products (.66 MeV vs. 2 MeV). This results in a roentgen response for e513? that is 0.4] times that for the inventory taken as a whole. At some time after burst, when cst3? is the only remaining fission product y-emitter, the dose rate is given by D(T) = D(1 hr) [6.1x107 7 x 0.41} (0.5)'/3° where T is in years. Note that beta activity is not being considered here on the presumption that the survey techniques distinguish between Enclosure S008 416 (2)