0018933 stratosphere at which the rate of injection of radioactive bomb debris will be equal to the decay plus deposition rate. A concensos reached at the 1957 Congreszional Committee hearings on fallout placed the permissible rate of testing zt 2-10 MT. per year (Reference 24}. The validity of such numbers depends in large pxrt on the reliahility of experimental detsrrainations of the fraction of the wezpen appearing in global fallout, This fraction hrs usually been estimzted indirectly by mezsuring the fallout in the local arez and subtraction from unity, The methods used for the determinztion of local fzllout have invelved measurement of gemma ray field contours or representative sampling cf the material arriving at the surface of the earth (References 25 and 2&}, The totzl amount of radio- active debris in the fallout area may be celculated if the relation between dose rate and surface density of radioactive m2teriz] is known, Similarly, semples representing 2 known area of the fzllout field may be znzlyzed for araount ef weapon debris and 2ll such are2s summed to give the total local fallout, A combination of fallout sampling and enzlysis plus gamma radia- fica mes.surements has also been used (Reference 26}, These procedures are subject to 2 number of difficulties and una car tainties, not only with regzrd to making adequate sample collections “and rzdistion field msasurements, but also in data interpretation, The es- treblishment of accurate gemma contours requres an extensive and costly