a theoretical construction and carries along all the inherent uncertainties, both physical and biological, which have been discussed in many of the preceding sections of this report. The numbers generated in the above paragraph are cited, not as absolutes, but as relative values, to point up a significant relationship: namely, that a local area may be lerge enough to be regarded as a critical geographical parameter. This local area will be above the safety levels for strontium-90 long before this situation exists on a world-wide basis if the contamination is brought about by surface bursts of nuclear weapons. . It may be superfluous to point out that the problems faced by those of the target population left alive after having been hit by 750 one megaton bombs would be likely to be such as to make that of accumulating one microcurie of strontium-90 in their bones over the next generation or so a very secondary consideration. It seems apparent that a military requirement which would result in mounting such an attack against a population would be so over-riding as to ignore the possibility of carcinogenesis in the remnants of the population some 20 years later. On the other hand, if the 50% of the strontium-90 which does not fall out locally on the target area is distributed uniformly worldwide, then the bone deposition outside the local area would be 1.54x10" microcuries, and thus 2 x 25,000 MI = 50,000 MI of surface burst | weapons on any target area would be required to bring the world outside that target area to the 1 microcurie bone level. in relating to atmos- _pheric or other storagemechanisms,stillunresolved. Thereis ~considerable evidence pointing to stratospheric storage of radioactive material, but the quantity of material involved and the rate at which it descends are still in dispute. The British have estimated that half the material located above the tropopause will descend from the stratosphere into the troposphere every 5 years and that the material will 18 2