Relative Biological Effectiveness (RBE) and Dose Rate Dependent Ratio of Translocation to Dicentric Chromosome Yield in 252 Cf Neutrons

Abstract

The relative biological effectiveness (RBE) of 252 Cf neutrons at different dose rates (2, 0.2&0.02 cGy/min) was assessed in human lymphocyte and bone marrow cells using cytogenetic end points (by Giemsa staining). The RBE values for 1 Gy of 252 Cf neutrons for chromosomal aberration yield in lymphocyte at the dose rates of 2 and 0.02 cGy/min were 3.3 and 12.0, respectively, in comparison to that of 60 Co γ - or 137 Cs γ -rays. RBE values of Cf(n) in human bone marrow were determined for the first time in the present study, and were 6.5 for chromatid-type and 4.4 for chromosome-type aberrations at the dose rate of 2 cGy/min. These values were higher than those of lymphocytes obtained in the present study. As studied by FISH method, the exposure of 252 Cf neutrons and 60 Co γ - and 137 Cs γ -rays at different dose rates also revealed the fact that the ratio of the dicentric chromosome yield to the translocation yield was influenced by LET and dose rates. No dose rate effect was found for the induction of dicentric chromosome aberrations. But an increase in the incidence of translocation was observed in the 252 Cf neutrons exposure at a dose rate of 0.02 cGy/min. These results suggest that the formation of dicentrics and translocations differed with source of radiation and dose rate.