- 62 the highest dose (mrad per picocurie per milligram of iron) is delivered to ferritin aggregates as compared with red blood cell or the whole body. How- ever, the integral dose (gram-rad per picocurie per milligram of iron)is "inversely related and the smaller entities,such as ferritin, aggregates receive smaller integral doses than the red blood cells or the entire body. The dose to ferritin aggregates is several orders of magnitude greater than that to red cells whereas the integral dose to ferritin aggregates is less than that to the red cells. On must also consider the possible effects of radiation on different targets. That is, circulating red cells do not divide and the ferritin aggregates within the entire human body contain roughly 400 milligrams of stable iron. Calculations were made of the total (infinity) dose to various biological ‘ entities of New York residents in 1965 arising from average concentrations of 3.4 picocuries of iron-55 per milligram of iron. The results indicated doses of 1.4, 0.46 and 235 millirad for the red cells, red marrow and ferritin aggregates, respectively. However, the integral doses for the red cells, red marrow and ferritin aggregates were 3.5, 0.69 and about 0.5 gram-rads. Question 12C Is it true that in 1960, the ICRP maximum permissible concentration of strontiwum-9O was 33 picocuries per litcr of milk, but that in 1962, the Federal Ra@intion Council raised the acceptable concentration to 200? If so, what changed the earlier benefit-vs-risk judgment? Had the risk gone down, or had the benefit gone up? Answer 12C The basic radiation protection standard for strontium-90 has been the