Abstract
Abstract The rate of induction of reciprocal translocations by fast neutron irradiation of mouse spermatogonia was studied by cytological examination of descendant spermatocytes. With acute irradiation (49–55 rad/min) the frequency of affected spermatocytes rose to a maximun of 8.7% at 100 rad, falling abruptly at higher doses to 1.6% at 220 rad. With chronic irradiation over 12 weeks, however, no such fall-off was found. Instead, the yield at 214-rad neutrons was 21.7%, while that at 62-rad was 3.3%, which is significantly less than expected on a linear hypothesis. If one assumes linearity at low doses, the neutron-X RBE for acute irradiation is about 4 and the neutron-γ RBE for chronic irradiation is about 20–25.
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