SMOKY external gamma-exposure fields based upon the individual radionuclides and their gamma emissions, and has shown that po #38 is a better approximation over longer time periods. | _ Also, the use of this infinite exposure model does not represent realistically the exposure received by people because no provision is fade for the shielding provided by residences, workplaces, schools, or automobiles. These twoproblems were recognized and addressed by Dunning (Du57a,b). ‘Based upon measurements of the external gamma-exposure field on the [stand of Rongelap over a two-yr period (reproduced in Fig. 1), Dunning developed the following mode] as a more realistic fpN expression of the externgl\ exposure rate in a real open-field situation where fallout is weatheringtinto soil: a a. cr = R(1) t"'*4 fom”st 168 hr R(t) = <bR(1) 7°? “1.3 for 168.hr< t < 336 hr [7] cR(1) t “1.4 for 336 Hr <_t where b and c are constants required forcontinuity. The estimated exposure (EE) experiencedby people over a one-yr period is then calculated as FE =5§ ~ 8760 a . R(t) dt TT _ where 3 is a building shielding factor of 0.75. (8) Tirts-was_based upon the experimental observation that buildings reduce exposure by an average factor of two (DuS7a) and the assumption that people are in buildings half the time. The solution of the above is 207