Relative Biological Effectiveness and Non-Poissonian Distribution of Dicentric Chromosome Aberrations after Californium-252 Neutron Exposures of Human Peripheral Blood Lymphocytes.

Cells exposed to fast neutrons often exhibit a non-Poisson distribution of chromosome aberrations due to the high ionization density of the secondary reaction products. However, it is unknown whether lymphocytes exposed to californium-252 (252Cf) spectrum neutrons, of mean energy 2.1 MeV, demonstrate this same dispersion effect at low doses. Furthermore, there is no consensus regarding the relative biological effectiveness (RBE) of 252Cf neutrons. Dicentric and ring chromosome formation was assessed in human peripheral blood lymphocytes irradiated at doses of 12-135 mGy. The number of aberrations observed were tested for adherence to a Poisson distribution and the maximum low-dose relative biological effectiveness (RBEM) was also assessed. When 252Cf-irradiated lymphocytes were examined along with previously published cesium-137 (137Cs) data, RBEM values of 15.0 ± 2.2 and 25.7 ± 3.8 were found for the neutron-plus-photon and neutron-only dose components, respectively. Four of the five dose points were found to exhibit the expected, or close to the expected non-Poisson over-dispersion of aberrations. Thus, even at low doses of 252Cf fast neutrons, when enough lymphocyte nuclei are scored, chromosome aberration clustering can be observed.