139. In the field of inhaled alpha-emitters an experimental study in rats treated with 238 EL, e395, and a Am given as oxides or nitrates was reported recently [M19]. Survival time of the animais and latency time, frequencey, location and histotype of the tumours were analyzed as a function of the dose rate and of the dose distribution. An acceleration of the tumour induction time (and therefore of aftersurvival time) with increasing dose and the existence of a non-neoplastic life-shortening at high doses were also apparent. Similar findings were also obtained in dogs inhaling 2395, py Bair [B16] and by Park [P1]. 6. 1hO0. Conclusions The effect of life-shortening induced by continuous exposure may be analysed as a function of the dose=rate of the treatment or against the total dose received (at the various dose rates) from the beginning of exposure to death. There is enough data in the mouse to examine both types of dependen- cies and to attempt some descriptive analysis. wut. Figure IX shows on the ordinate the percent life-shortening induced af- ter exposure at the dose rates indicated on the abscissa in rad/day. available on various strains and sexes have been grouped, case of neutron and low-LET radiations. separately for the The graph includes therefore all the variability expressed in this type of experiments. that the data by Moos et al. All data It should be pointed out [M14, M15], although following qualitatively a Similar trend, have quite different quantitative relationships and could not be considered with the other series. The x— and gamma-ray data include 5 diffe- rent series performed on 4 strains of male and female mice; the neutron data include 5 series on 3 strains and both sexes. the. The nature of the plot in Figure IX is such that the low dose-rate end of the abscissa is greatly expanded. ¥ where A Sigmoid relationships of the type 100 (1 - eB) (16) is the dose-rate in rad/day may reasonably be fitted to the data. When a non-weighted curve was fitted to the data by a least-square method, the solutions were, in case of the low-LET radiation