radiation may be measured by an "Equal Effectiveness Ratio", a quantity defined as the ratio of the standard radiation dose to the densely—ionizing radiation dose producing the same level of effect. The present document will not dis- cuss the theoretical foundations of these concepts which are reviewed elsewhere [K10, R4] and are discussed in other annexes of the UNSCEAR report. It will only consider evidence regarding life-shortening, according to the order of publication. 193. The early experiments on neutron RBE by Henshaw [H6], Evans J|E2), Gowen [G8] and Neary et al. [N3] will simply be cited. They were analysed by the 1958 report of the Committee [U1] which discussed all data in the rodent irradiated chronically and summarized them in one graph [M13] (see Figure XIV). The percentage mean survival time was plotted versus the gamma-ray or the fast neutron exposure- or dose-rate in R or rad/week. The data appeared to be superimposable when the gamma- and neutron-scales were in the ratio of 1:13. From this it could be ‘deduced (in spite of some uncertainties in the comparison of data from different laboratories) that the RBE between fast neutrons and gamma rays applicable to life-shortening in the rodent for chronic durationof life-exposure was about 13. 194, A study of x rays (250 kVp, 185 rad/min) and of fast neutrons (fission spectrum, 2.7 x 10 neutrons/em“/sec) was performed in CF1 female mice by Curtis and Gebhard [C17]. In a first series, single doses (474-641 of x rays and 280- 330 rad of neutrons) were used; in another experiment mice received 35 per cent of the LDS 9/30 of both radiations once a week for 4 weeks; in a third series 50 per cent of the LD 50/30 was given once every two weeks for 4 weeks. for life-shortening was estimated at 1.7 for all series. The RBE These results are dif- ficult to interpret not only for the lack of an increase of RBE with fractionation, but also for the low RBE value of the acute exposures. 195. When straight lines were fitted to the data of Upton et al. [U5] on LAF1 mice irradiated with gamma rays or fast neutrons from a nuclear explosion, very similar RBE values of 2.1 and 2.3 were obtained in male and female animals, respectively. Mole and Thomas [M7] estimated the RBE of fission neutrons against Co gamma with the same source of radiation and the same animals as reported previously [N1, N3, M13]. The life-shortening effects of 16-17 rad/week of fast neutrons or of 210 and 110 R/week of gamma rays were found to be equivalent both for terminated and for duration-of-life exposures. For all levels of re-