The mutagenic effectiveness of 8.5 and 24.5 keV neutrons in Barley

Abstract

The mutagenic effects of intermediate energy neutrons of 8.5 and 24.5 keV are compared with those of of higher energies (100 and 200 keV and fission neutrons). Due to the low dose-rate of intermediate neutrons and the small space available for irradiation, embryos of resting seeds of Bonus barley were used for the study. The relative biological effectiveness (RBE) of these neutrons was obtained by comparison with the effectiveness of 180 kV X-rays in inducing chlorophyll mutations. The following RBE values of mutagenic effectiveness of neutrons of different energies were found (with 80% confidence intervals); 8.5 keV: 0 (neg.−3.3); 24.5 keV: 21 (12–33); 100 keV: 204 (120–330); 200 keV: 102 (49–190); fision neutrons, ∼ 1MeV: 37 (29–47). However, the difference in RBE between 100 and 200 keV neutrons was not significant in the present case. The low mutagenic effectiveness of low-energy neutrons can be ascribed mainly to the short range of the charged particles. According to the two-hit theory for the induction of chromosomal aberrations by ionizing radiation, this would mean that mutations induced with the high RBE of high-LET radiations are mainly chromosomal aberrations (multi-locus deletions).