Neutron-Induced Genetic Effects: A Review

Abstract

Abstract Early studies of the production of gene mutations and chromosomal aberrations by neutron irradiation of various plant and animal systems suffered from difficulties in establishing neutron dose. Gene mutation studies yielded estimates of relative biological effectiveness (RBE) of less than unity. More recent work incorporating more accurate dosimetry has shown that this value is always greater than one, and have established RBE values, dose-effect kinetics and dose rate effects for a variety of genetic end-points. In spite of a rather large variability among the results reported by various authors, it appears that several rather general conclusions can be drawn, at least regarding the genetic effects of fast neutron irradiation. 1. It seems clear that RBE values are always at least one and often much greater. 2. RBE values are much lower for point mutations than for chromosomal aberrations in animal cells. 3. RBE values are larger in plant than in animal cells, and similar for mutation and for chromosome aberration production, supporting the idea that most plant mutations involve chromosomal rearrangements. 4. RBE is a function of neutron energy, increasing with increasing LET to a maximum at around 60 KeV/μ and then decreasing again at higher LET. 5. Neutrons induce multiple-hit events which have non-linear dose-effect kinetics for low LET radiations as a linear function of dose. 6. Neutron effects are in general much less subject to modification by other parameters, such as dose rate or oxygen in tension, than are low LET radiations. Thermal neutrons deposit energy in tissue by capture rather than by production of a recoil proton, making determination of their relative effectiveness dependent on precise determinations of the energy deposited from proton and α particle production and from prompt and delayed β particle and γ ray production. Determination of thermal neutron RBE for chromosomal aberration production has yielded values about three times greater than would have been expected from the same doses of the various capture radiations given externally. The RBE for mutation production appears to be similar to that for fast neutrons.