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.
Highlights
relative biological effectiveness (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 results suggest that the formation of dicentrics and translocations differed with source of radiation and dose rate
Previous reports have shown that low doses of fission-spectrum neutrons delivered at low dose rates enhanced the neoplastic transformation of mouse C3H10T1/2 cells and 6-thioguanine resistant (6-TGr) mutations of mouse L5178Y cells (Hill et al .,1982; Miller et al, 1988; Nakamura & Sawada 1988)
Summary
The RBE values of Cf and Cf(n) in the lymphocytes were 2.14 and 3.24 at an aberration yield equivalent to 2 Gy, and 2.45 and 3.63 at an aberration yield equivalent to 0.5 cGy. The RBE values at the three dose rates of 2, 0.2 and 0.02 cGy /min at an aberration yield equivalent to 1 Gy were 2.3, 7.6 and 7.7 for Cf, and 3.3, 11.0 and 12.0 for Cf(n), respectively. Yields of chromosome aberrations and RBE in bone marrow cells. The dose-response relationships in bone marrow cells at the dose rate of 2 cGy/min are shown in Table 2 & Fig. 2. Chromosome aberration yields of dicentrics plus centric rings and chromatid
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