Table 2— TESTS STOP IN DECEMBER 1957 {Units in millicuries per square mile) (2) Deposition (12/57) Stratospheric content (12/57) Fraction removed per year (2) 25 14 (28 Mt) 0.1 Stratospheric nonuniformity factor 25 11.5 (23 Mt) 0.2 1.0 3.0 5.3 19.6 Fallout, maximum from Sr® now in the stratosphere 25 me/sq. mile decayed to maximum Total fallout Time of maximum 21.6 22.0 27 1963 42 1962 (5.8 yrs.) (5.2 yrs.) Table 3—-TESTS CONTINUE AT SAME RATE* (Units in milicuries per square mile) A Tropospheric fallout to 12/57 B 21 6 21/4 6/4 to 12/57 Stratospheric 4 19 nonuniformity factor Fraction removed per year 1.0 3.0 0.1 0.2 Tropospheric injection rate, mc/sq. mile/year Stratospheric fallout Prediction of fallout at equilibrium (about 100 years) Accumulated tropospheric Accumulated stratospheric 210 60 144 x1 = 144 160 x 3 = 480 Total accumulated 354 540 *Common assumptions: total fallout = 25 at t = 4 years; stratospheric injection rate = 9 Mt/year or 4.5 mc/sq mile/year. scribed by Dr. Libby. On the other hand, some local values might be higher owing to smallscale meteorology and soil anomalies and dietary peculiarities. It appears that, despite wide differences of interpretation of the fallout mechanisms, the uncertainties of deposited fallout on the ground are smaller—by perhaps an order of magni- tude—than the conversion of this fallout to Sr** human bone content. The interpretations of hazard from a given predicted Sr*° bone content allows even larger differences of opinion than the forecast of how much Sr® will be in man. 7 CONCLUSIONS The technical conclusions drawn from the discussion are: (1) From evidence of total Sr fallout and tropospheric fallout, it is found that the stratospheric fallout fraction is markedly nonuniform and has a peak in the temperate latitudes of the northern hemisphere, (2) A seasonal variation in the rate of fallout is present which is probably due to variations in atmos- 337 ms