Variation of RBE between p(75) + Be and d(50) + Be neutrons determined for chromosome aberrations in Allium cepa

The RBE of p(75) + Be neutrons relative to d(50) + Be neutrons has been determined for chromosome aberrations induced in Allium cepa (onion) roots. Two biological criteria were selected: the average number of aberrations (mainly fragments) per cell in anaphase and telophase, and the percentage of aberration-free cells. The influence of sampling time (3 to 7 h incubation) between irradiation and fixation was investigated systematically. This factor did not significantly influence the results. The RBE values of p(75) + Be neutrons compared to those of d(50) + Be neutrons were 0.85 (0.79-0.91) and 0.87 (0.80-0.95) for the first and the second criteria, respectively. In previous experiments for the same beams, we found an RBE of 0.90 (0.86-0.94) for survival of V79 cells (D0 ratio), 0.96 (0.93-0.99) for the intestinal crypt cell system, and 0.83 (0.70-0.96) for Vicia faba growth delay.