mean unweathered activity per unit area were not well defined, it is thought the calculated mean activities per unit area at Rongelap Island had a standard deviation partly based on the original Bikini Ash measurements (e.g., Zr-95, S.D. = 420%, (Is56)) and partly based on the point to point variation reported in soil samples taken from the surface of Rongelap, Sifo and Utirik Islands. The mean day 26 unweathered activities per unit area for the 25 nuclides in Table 4 were tabulated in Table 5 columm 5. The standard deviation of the mean unweathered activity per unit area would be greatly affected by random fallout deposition and physical mechanisms which move deposited fallout around. This standard devi-~ ation was estimated to be plus or minus 140% of the mean value. This was based on the variation in surface activity measurements reported by O'Conner (0C68) for surface samples taken from the Northern Marshall Islands following BRAVO. The estimates of mean unweathered activity per unit area due to BRAVO fallout on Rongelap Island were extrapolated back to 0.5 days post deto~ nation and results listed in Table 5. The 0.5 day post detonation time was cho- sen to represent a point in time at which the fallout at Rongelap Island had probably ali been on the ground (Sh57). First order linear kinetics for seri- ally related nuclide species (Bal0) and decay schemes from Table of the Isotopes (Le78) were used to calculate the 0.5 day activity from the day 26 activity. The mean unweathered activity per unit area for short-lived precursor nuclides not set present on day 26 but on the ground at the end of fallout at 0.5 days were calculated and also listed in Table 5. ce. Areal Activity of Nuclides Without Descendents in Bikini Ash Many short-lived nuclides had no daughter radionuclides present on day 26. The activity of these short-lived nuclides was based on the ac~- tivity of a reference nuclide. An equation was used to relate the unknown activ~ 17