ven Tevet acerity Ge x The individual contributors to exposure cannot be readily summed except in the form of radiation dose. This has not been done in the present case but the summary from the 1966 report of UNSCEAR is included here as table 16. Generali Notes The numerical values have been rounded off sometimes even beyond the rounding done in the original compilation. Since the values are intended to represent the average over large areas there is little meaning to using more than one oth of gil rir omp significant figure. In many cases it has been necessary to convert the units from those of the original compilation and in a few cases it has been necessary to calculate values from basic handbook information. Those calculations relating to man are all on the basis of a 70 kg standard man with 2800 grams of skeletal ash. Tritium (Table 1) rac La 4 Natural tritium is produced in the atmosphere by cosmic ray bombardment at the rate of 0.5 to 0.6 atoms/sec per om*. This corresponds to an annual producticr rate of about 2500 pCi/m@ of the earth's surface. been estimated at 70 to 65 megacuries. The equilibrium inventory has The complete assessment of the environment had not been finished at the start of thermonuclear weapons testing and the data are not completely firm. Since tritium is produced in the stratosphere, the highest natural concentrations are in atmospheric hydrogen, water vapor and in precipitation. Older waters such as those from the deep oceans and deep wells have extremely iow concentrations while surface waters from the continents and the ocean are intermediate. The specific activity of natural tritium in man is generally lower than surface waters.