= 0.0125x1072 0 : 9 r/hr (natural background) = 0.0181x10"7 r/hr, the dose rate of cesium-137 required at H+l hour to give the desired dose rate at 2O years. ec. Then, to obtain the curies of cesium-137 per square mile needed to give 0.0125x107" r/hr at 20 years, 1 megacurie/mi- - 4 r/br x 0.0181x10°? r/hr x = 4.5 curies cesium-137/mi° at H+l hour to double the background at 20 years. d. Then the fission yield required would be, 3.5x10 “2 curies/mie KT/curie cesium-137 = l.lxto! xr = 1.1210" mr. The result indicates that 1.1x10’ KY or 1.1x10" mr must be produced in order to double the background by gamma radiation at 20 years. Because the spontaneous mutation rate is only partly due to background radiation, the numerical estimate of 1.1x10+ MI given above probably represents a lower limit to the value of fission yleld required to double the spontaneous mutation rate. A non-uniform world-wide distribution would alter this figure in direct proportion to the non-uniformity of the distribution in the major area under consideration. Finally, mention should be made of the spontaneous abortion rate. According to one authority, "a conservative estimate would indi- cate that about every fifth pregnancy in private practice ends in spontaneous abortion, and the percentage would increase considerably were the very early cases taken into account .”25/ Since abortions are genetic deaths, it can be seen that the population of 100,000,000 discussed above, with its 2,700,000 births per year would have in excess of 500,000 abortions annually to be counted as genetic deaths independent of any artificial radiation experience. It is also worth 35/ Stender, H.J., Williams Obstetrics, Sth Edition, Appleton-Century 94