0018933 stratosphere at which the rate of injection of radioactive bomb debris will be equal to the decay plus deposition rate, A concensus reached at the 1957 Congressional Committee hearings on fallout placed the permissible rate of testing at 2-10 MT per year (Reference 24), The validity of such numbers depends in large part on the reliability of experimental determinations of the fraction ef the weapon appearing in global fallout, This fraction has usually been estimated indirectly by measuring the fallout in the local area and subtraction from unity, The methods used for the determination of local fallout have involved measurement of gamma ray field contours or representative sampling of the material arriving at the surface of the earth (References 25 and 26). The total amount of radio- active debris in the fallout area may be calculated if the relation between dose rate and surface density of radioactive material is known, Similarly, samples representing a known area of the fallout field may be analyzed for amount of weapon debris and all such areas summed to give the total local fatlout, A combination of fallout sampling and analysis plus gammaradia- tion measurements has also been used (Reference 26), These procedures are subject to a number of difficulties and uncertainties » not only with regard to making adequate sample collections and radiation field measurements, but also in data interpretation, The es- tablishment of accurate gamma contours requires an extensive and costly 24 a SAN BRENG FRE , at