Lethal and Hematologic Effects of 14.6 MeV Neutrons on Beagles with Estimation of RBE

Beagles from our colony were exposed in plywood boxes to 14.6 MeV neutrons from Lawrence Radiation Laboratory's insulated core transformer. Hematologic response was followed in a small group and the ${\rm LD}_{50(30)}$ determined in 82 dogs. The ${\rm LD}_{50(30)}$ for 1 MVp x-rays was confirmed with similar dogs from the colony, irradiated and maintained under nearly identical conditions. Neutron dosimetry was performed utilizing an appropriate phantom. The hematologic response to 189 rads midline exposure volume dose (MEVD) or 136 rads midline tissue dose (MTD) of 14.6 MeV neutrons is presented. The ${\rm LD}_{50(30)}$ was 379 rads (MEVD) with 95% confidence limits 349-461 rads (MEVD) based on 82 dogs, while the corresponding values for x-ray were 326 R (363-295) (MEVD) utilizing 24 dogs. Dosimetric data are presented in support of the estimate of neutron ${\rm LD}_{50(30)}$ of 281 rads (MTD) (including 3% γ-ray contribution) compared with x-ray ${\rm LD}_{50(30)}$ of 288 rads (MTD). Thus the RBE of 14.6 MeV neutrons compared to 1 MVp x-rays is 1.01. These results are discussed and compared with previous neutron irradiation results in dogs.