of Technology for the past 10 years. Their recordings indicate no change in the gamma radiation values during that entire period, except for short periods of time when an atomic cloud is known to have passed overhead following a test detonation. The data from which the material of this section has been drawn was compiled by several laboratories. The levels of contamination by strontium-90, world-wide, are so low that large samples have to be processed for analysis. Consequently, carefully trained personnel have been utilized on the SUNSHINE studies, and the equipment has been de- signed especially for the low level counting necessary. It is consid- ered that in spite of the difficulties involved good analytical results have been obtained. The gummed paper results have been subjected to much serutiny and have been questioned by many because the results of one sampling station collecting fall-out on one square foot of surface are extrapolated to areas of thousands of square miles. However, the personne] at the New York: Operations Office feel confident that their results can be de- fended and that they should be considered + 30% to 50% reliable. IIT. BIOLOGICAL ASPECTS OF THE FALL-OUT PROBLEM A. Evaluation of the Human Hazard Due to Radioactive Fall-out: External. Several parameters need assessment in order to evaluate the external hazard to humans from fall-out radiation. The effects of whole body radiation with regard to its lethality, sickness, and genetic potentials are the most important factors to be considered. ‘The beta burn problem also requires evaluation. The biological phenomena concerned are extremely complex and only the grossest type of classification of hazard can be attempted. How- ever, for large scale populations, gross estimates of lethality, sickness, etc., probably suffice to define the problem. In setting allowable limits of exposure to avoid the hazard range, the problem of bias toward setting standards of safety enters the 62