- Results of Calculations of External Gamma Radiation Exposure Rates from Local Fallout and the Related Radionuclide Compositions of Selected U.S. Pacific Events Abstract This report presents data on calculated gamma radiation exposure rates and local surface deposition of related radionuclides resulting from selected U.S. Pacific events. Introduction In the past, wehave calculated the normal- ized external gamma radiation exposure rates that resulted from local fallout from the Nevada Test Site (NTS).' These calculations have been used in Table 1. Date, placement, and yield of selected U.S. Pacific events. Event Date Placement the reconstruction of radiation doses downwind of NTS. More recently, we were asked to make Mike Bravo Oct. 31, 1952 Feb. 28, 1954 Surface Surface of doses to personnel participating in nuclear tests Yankee May 4, 1954 Barge similar calculations to assist in the reconstruction in the Pacific. This report contains the results of these calculations that we made and that were used by the Nuclear Test Personnel Review of the Defense Nuclear Agency and its contractors. Romeo Zuni Tewa Mar.26, 1954 Barge May 27, 1956 Surface July 20, 1956 Barge Yield (MT) 10.4 15.0 11.0 13.5 3.5 5.0 The selected U.S. Pacific events’ are listed in Table 1. Results Results of the calculations of relative external gamma radiation exposure rate and related radionuclide ground deposition are given in the Appendices. These calculations are described in detail in Ref. 3. The output of the calculation has 30 decay times: 10 from 1 to 21h, 10 from 1 to 300 d, and 10 from 1 to 50 y. For each of these times and for zero time, there are values of the external gamma radiation exposure rate normalized to 1 mR/h, 1 m above the surface, 12 h after the event; the associated values of uCi/m* for each radionuclide; and the total wCi/m?, Surface roughness effects are simulated by using Beck’s values’ of (mR/h)/(uCi/m?) for a re- laxation length of 0.16 g/cm*. According to Beck, the concentration of fallout varies exponentially with soil depth, Z, according to the relation C = C,e~"*. He defines relaxation length as 1/q. Fractionation effects were simulated by the removal of a fraction of the refractory nuclides from the calculation. Calculations for each event were performed for unfractionated debris and tor debris with 0.5 and 0.1 of the refractory elements present. Each Appendix contains three sets of 11 pages of calculated results relating to one event in Table 1. Each set of 11 pages is marked Page 2 through Page 12. Page 2 of each set gives the external gamma-ray exposure rates and associated values of total microcuries per square meter at 30