RBE of quasi-monoenergetic 60 MeV neutron radiation for induction of dicentric chromosomes in human lymphocytes

The production of dicentric chromosomes in human lymphocytes by high-energy neutron radiation was studied using a quasi-monoenergetic 60 MeV neutron beam. The average yield coefficient (alpha) over bar of the linear dose-response relationship for dicentric chromosomes was measured to be (0.146 +/- 0.016) Gy(-1). This confirms our earlier observations that above 400 keV, the yield of dicentric chromosomes decreases with increasing neutron energy. Using the linear-quadratic dose-response relationship for dicentric chromosomes established in blood of the same donor for Co-60 gamma-rays as a reference radiation, an average maximum low-dose RBE (RBEM) of 14 +/- 4 for 60 MeV quasi-monoenergetic neutrons with a dose-weighted average energy (E) over bar of 41.0 MeV is obtained. A correction procedure was applied, to account for the low-energy continuum of the quasi-monoenergetic spectral neutron distribution, and the yield coefficient alpha for 60 MeV neutrons was determined from the measured average yield coefficient (alpha) over bar. For alpha, value of (0.115 +/- 0.026) Gy(-1) was obtained corresponding to an RBEM of 11 +/- 4. The present experiments extend earlier investigations with monoenergetic neutrons to higher energies.