The RBE of 30 kV X-rays for the induction of dicentric chromosomes in human lymphocytes.

The frequency of dicentric chromosomes induced by the irradiation of human lymphocytes in Go phase was determined with hard (150 kV) and soft (30 kV) X-rays. When a linear-quadratic dose-effect relation was used to fit the experimental data, a significant linear contribution was found for 30 kV X-rays. The RBE of 30 kV compared with 150 kV X-rays approaches the value 3 at a 30 kV X-rays dose of 20 rad and decreases with increasing dose. From the results it may be concluded that chromatids with primary breaks, undergoing second order reactions and thus forming dicentric chromosomes, are produced by traversals of low-energy electrons through chromatin material.