UNCLASSIFIED —— oe ae ee is completely absorbed in that organ. The dimensions of the organs of mice are such that a considerable fraction of the more energetic beta particles may not be stopped in the organ and thus may expend their energy in other tissues. The organs in man, on the other hand, have dimensions sufficiently large as compared to the range of the beta par- ticles to make valid the assumption of the equivalence of energy emis sion and absorption. Thus by extrapolating the values of concentration and distribution as observed in the mouse (based on the assumptions of similar organ distribution and similar ratio of organ sizes in mice and men), calculation of dose may be made in man. With these assumptions the relative dose that might be received by the various organs of man following an exposure to a dry-particle Sr90Cl2 aerosol were calculated. The Sr concentration in organs as determined from measurements of the Sr®5 tracer (gamma activity per gram of tissue) are listed in Fig. 4. Values for the initial relative dose rate (at 0.5 hour) and the total relative dose*™ (28-day period) are presented in Table 6, based on 100 percent for the skeleton. At early times following inhalation, the stomach and the G.I. tract receive the highest dose rates, due to the heavy concentrations of activity. Measurement of the stomach and in- testine was done on the whole specimen, including its contents. The intrinsic geometric and self-absorption factors involved in the deter- mination of the beta dose to the mucosa of the stomach andintestine, which have been neglected in this simplified calculation, would markedly reduce the dose as listed in Table 6. The rapid excretion of activity is reflected, however, in the dose calculations, which indicate that by far the highest total dose is delivered to the skeletal system, which "fixes'' Sr and releases it only very slowly (rate constant \2= 0.019/day, equivalent to t)/2 = 36 days (see Table 5)). The dose to the head is the next largest, about one-fourth that received by the total skeletal system. The components of the G.I. tract are next in order, with the large intestine receiving more than twice the dose to the stomach and small intestine and twice that delivered to the respiratory tract and lungs. ~*The doses were calculated mathematically, with the use of the con-: stants obtained for the biological decay curves (Table 5) and were checked by mechanical integration of the curves performed with a planimeter. -16- =E ££ £€ EF KR 68 EF wf bL 2 £2 £E B&B kc £§ fF £