Gt Question 12A . Do you, or any of your colleagues, have any reason to think that the acceptably safe? ~ * ‘b .. ~ “acceptable,” "safe," "permissible" doses of radiation may not be ‘Answer 12A No. Question 12B A study by Warren A. Brill at the National Center for Radiological Health concludes that an acceptable dose of iron-55 to the spleen probably re- sults in a dose two times higher to the red blood cells, and 800 times _ higher to the blood ferritins. experts? Is this conclusion accepted by other Answer 12B The conclusion was drawn by Warren A. Brill, although the information is primarily a summary of work done by other investigators. It is interesting to notethat problems related to iron-55 dosimetry in various biological entities have been under study for about a decade. Various organs such as the spleen, tissues such as blood and tissue components such as erythrocytes or ferritin aggregates have been investigated. The conclusion stated in the question is generally accepted by those knowledgeable in the field of dosimetry. We should be aware, however, of exactly the energy is absorbed, by what biological entity For itron-55 the energy available for deposition in biological systems averages about 6 keV (the ICRP uses a more conservative value of 6.5 keV). Auger electrons. The energy is emitted either as X-rays or as short-ranged The Auger electrons account for about 80% of the available energy so that, for cells containing high concentrations of iron-55, most of the decay energy is deposited within the cell. Because of this short range