sree a ~d— equivalents per day. 4, The probability ie~that at least 10° bombs would have to be exploded in the U.S,S.32. to give a nrobability of 1 that a nergon in the U.S.A, would receive one particle, based on somewhat Simplified caiculationa, 5. The significance of a single particle has yet to be determined. It is my nersonal feeling that it would be relatively slight and that multiple particles would be required before producing either significant necrosis of the lung or pulmonary cancer. Con¢glusion: present time. The pulmonary hazard cannot be evaluated at the (C) Absorption of nlutonium follewing inhalatfon and subse- quent deposition in the skeleton. 1. This cannot be evaluated at present and is probably much less of a hagard than either (A) or (ay (D) Zxternal radiation from the fission vroducts. 1. This is negligible except in immediately local areas. Studies made previously indicate fantastic numbers of bombs would be required for significant effect, RECOMMENDATIONS 1. In the light of oresent knowledge 3 x 10° bombs should be taken as the number which will probably cause gerious damage to personnel through crop contanination if detonated within one growing season and within an area of 350,000 square miles. 2. Obvtaining of further experimental data on the significance of radioactiys particles wit in the lung and on the metabolism in aumans of atrontium™? piltis yttrium’ should have high priority. 3. At a subsequent test air burst detailed studies of particle size and the long-range movement of particles should be made. Sincerely yours, SW:NF OFFICE » SURNAME | a a Shields Warren, M. 5, -- Director, Division of Biology and Medicine