The Microdosimetry of 250 kVp and 65 kVp X Rays, 60 Co Gamma Rays, and Tritium Beta Particles

Energy deposition from single events occurring in spherical sites ranging in diameter from about 50 to 550 μ g cm⁻² have been studied by means of a grid-walled proportional counter. Single- and multiple-event spectra from medium- and low-energy bremsstrahlung are compared to those produced by60 Co gamma rays and tritium beta rays. From these spectra the dose-mean specific energy from single events and the number of events per rad exceeding a given event size are calculated for sites of various diameter. The relevancy of these data to the Kellerer-Rossi theory of dual radiation action is discussed and for each of the radiations studied, an estimate is made of the dose range in which the biological effects vary linearly or as the square of the dose.