Radiation quality of tritium beta-rays: microdosimetric distributions for nanometer-size targets in a medium containing tritiated water

Theory of relative biological effectiveness (RBE) of tritium beta rays: bacteria killing effects of tritiated water

A new model is applied to bacteria exposed to tritiated water. In this model, the relation between the radiation quality, induction of single- and double-strand breaks in DNA and their repair in vivo can be reasonably described in terms of the microdosimetric distribution and the modification factors for single- and double-strand breaks in DNA. First, a mathematical formulation of RBE of tritium beta rays relative to an arbitrary reference radiation for killing effect on bacteria is derived on this model. Typical theoretical results on the survival curve parameters for bacteria exposed to tritiated water and RBE of tritium beta rays relative to 60Co gamma rays are presented. It is found that RBE of tritium beta rays depends on the ability of the cell to repair DNA damage. The present model is applied to the survival of Escherichia coli Bs-1 exposed to tritiated water and 7 MeV electrons. Although the average LET of tritium beta rays is remarkably higher than that of 7 MeV electrons, the experimental result that RBE of tritium beta rays relative to 7 MeV electrons is close to unity, is reasonably explained by the present model.