594 ADVENTURES IX RADIOISOTOPE RESEARCH 



for this difference, the notion of roentgen equivalent man (rem) was introduced, 

 replacing the notion of roentgen equivalent physical (rep). For a-rays 1 rem = 

 = 20 rep (or less), while for /3- and y-rays 1 rem corresponds to 1 rep. In the 

 course of the disintegration of 1 microcurie of ThB + ThC + ThC, thus the a-rays 

 emitted produced not more than 4.0 X 10-2 lep. We arrive at this figure by assum- 

 ing that the whole amount of ThB administered decays in the body. In fact, some 

 ThB is excreted previous to its disintegration. 



The mean energy of the jS-rays emitted by ThB and its disintegration products 

 is 0.42 Mevs. or 6.7 X 10"'^ ergs per particle. By a similar calculation, as described 

 above, we conclude that the y5-particles of 1 microcurie of ThB produce during 

 its life-time an aggregate dose of 1.1 X 10~* rep/gm. 



The upper limit of the radiation dose produced by the decay of the y-rays 

 of 1 microcurie of ThB and its disintegration products is obtained by assuming 

 all y-radiation emitted to be absorbed in the body. The mean energy of the 

 y-radiation emitted being 1.1 Mev., the number of rep produced per day per gm 

 body weight works out to 3.0x10—*. The upper limit of rem/gm produced by 

 1 microcurie of ThB + ThC + ThC. Decaying in the organism is thus 4.0 X 10— ^ -f- 

 + 1.1x10-1 -f 3.0x10-* —4.4x10-2. The dose actuaUy produced lies quite 

 appreciably below this figure. We applied in all our experiments less than 2 micro- 

 curies of ThB. Thus the total maximum dose administered was below 8.8x10-2 

 rem. 



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