SLIDE 19 Normalization of fallout activity to exposure rate. Beck recorded activity per unit area per unit exposure rate factors for a number of particulate gamma-emitting fission products and for a number of particulate activation products and residual nuclear materials as the ground as a result of weapons tests (Be80). The exposure rates at one meter above the surface of a planar source of unit area of Bikini Ash activity were calculated for each nuclide based on the data of Beck (Be80) and nuclide composition of the ash. By summing the product of each nuclide'’s exposure rate (relative to unit activity per unit area) and fraction of total activity represented by each nuclide in Bikini Ash, the exposure rate from Btkint Ash pes unit areal, | activity was estimated to be 1,12 x 10 mCi km“). Ckge s~ Bq m (5.8 x10 Rh By inverting this sum and multiplying by the fraction of each nuclide activity relative to the total Bikini Ash activity and the Rongelap exposure rate on day 26, we estimated the beta activity of each nuclide per unit area due to BRAVO fallout on the surface of Rongelap Island. The estimates of mean unweathered activity per unit area due to BRAVO fallout on Rongelap Island were extrapolated back to 0.5 days post detonation. The 0.5 day post detonation time was chosen by us as the point in time at which the fallout at Rongelap Island had effectively ceased (Sh57). First order linear kinetics for serially related nuclide species (BalO, Sk75) and decay schemes from Table of the [sotopes (Le78) were used to calculate the 0.5 day activity from the day 26 activity. The mean unweathered activity per unit area for any short-lived precursor nuclide, not present on day 26 but on the ground at the end of fallout at 0.5 days, was also calculated. AREAL ACTIVITY RELATED TO EXPOSURE RATE (R bh )Nuclide (Cim™*)Nuctide x (Ci) Nuctide (Ci)pikini Asn (Ci m™) Bikini Ash x (Rh) Measured X (RA™’.)piini Aah _ (R ho )ukin Ash (Ci m“)BikimAsh (Ci) Nuctide (Ci m)Nuctide (Ci) Bikins Ash = (Chim “JNuctia 24