Comparative Effects of Protracted Exposures to ⁶⁰Co γ-radiation and ²³⁹Pu α-radiation on Breeding Performance in Female Mice

Summary

Breeding performances are compared of hybrid female mice given ²³⁹Pu (5 or 10 μCikg⁻¹ body mass in 1 per cent trisodium citrate via the tail-vein), or kept in a 10 rad/day or 20 rad/day ⁶⁰Co γ-irradiation field (but mated in the control area), or unirradiated. Ovarian dose-rates from the injected plutonium were initially 0·8 and 1·7 rad/day, changing little thereafter; actual γ-ray dose-rates to breeding females averaged around 8 and 16 rad/day respectively. Both γ-ray treatments affected reproductive performance more than the plutonium injections, with respect to duration of fertility and to offspring per litter in successive 4-weekly periods, though overall mean litter-sizes were not significantly less than controls. The r.b.e. for these effects on reproduction, attributed to germ-cell killing, is about 2·5 for the α-particles vs. γ-rays, lower than for testis mass reduction in males. This low r.b.e. may be connected with inhomogeneity of α-particle dose within the ovary, but it is known that fission neutron versus gamma r.b.e.'s for impairment of female fertility are also lower than those for impairment of male fertility.