Laser line selection in an electric-discharge CO laser

Abstract

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 R B E of tritium p 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 R B E of tritium p rays relative to 6oCo y rays are presented. I t is found that R B E of tritium p rays depends on the ability of the cell to repair DNA damage. The present model is applied to the survival of Escherichia coli B , -, exposed to tritiated water and 7 MeV electrons. Although the average L E T of tritium p rays is remarkably higher than that of 7 MeV electrons, the experimental result that R B E of tritium p rays relative to 7 MeV electrons is close to unity, is reasonably explained by the present model.