Relative biological effectiveness of neutrons: induction of malformations in a mouse strain with genetic predisposition.

Female hybrid mice (C57BL/6J x HLG) were exposed to 0.5 Gy of cyclotron neutrons (mean energy 5.8 MeV) after mating with HLG males when embryos were at the early zygote stage. Uterine contents were examined on gestation day 19 for prenatal mortality and malformed development. The results were compared to those obtained after irradiation of zygotes with 1.0 and 1.7 Gy X rays. The number of malformed fetuses was greater than for the unirradiated controls. Gastroschisis was the main observation, but exencephaly was also observed. The neutron relative biological effectiveness (RBE) for the induction of lethal events and malformations in the [(C57BL/6J x HLG)F(1)x HLG] mice was estimated. This value is higher than that for the RBE calculated for the HLG strain, which is known to be more sensitive to radiation than the hybrids.