Tumour Incidence and Longevity in Neutron and Gamma-irradiated Rabbits, with an Assessment of R.b.e.

Abstract

Rabbits were kept for the whole of their natural life-span (6-9 years) after exposures of 440-1410 rad of gamma-rays or 180-550 rad of fission neutrons . Irradiated rabbits did not live as long as unirradiated controls but the difference was statistically significant only after the higher doses of neutrons . Earlier deaths were explained by increased incidences of a wide variety of tumours . The increases were statistically significant for basal-cell tumours of the skin, fibrosarcomas, osteosarcomas and Sertoli-cell tumours of the testis . Other phenomena associated with natural ageing were unchanged or decreased in irradiated rabbits .The r .b .e . of the neutrons was assessed as 3-3. 5 for tumour induction and 3 . 5-4 .0 for longevity . Comparisons with previous data on acute and subacute effects suggest that the r .b .e . increased linearly with the logarithm of time for 5-2000 days after irradiation .