Experimental microdosimetric distributions of protons, from 19 to 65 MeV, using an A150-walled low pressure proportional counter

Microdosimetric distributions of protons, from 19 to 65 MeV, were measured using an A150-walled Low Pressure Proportional Counter at the cyclotron facility in the National Inst. of Radiological Sciences. The measured distributions were found to be very different from the spectra assumed by the Continuous Slowing Down Approximation. The measurements consisted of determining the energy deposition by direct incident protons, by secondary electrons produced in the wall of the detector and by scattered protons at the wall. The secondary electron and the scattered proton distributions were studied using analytical functions and the MCNPX Monte Carlo code, respectively. (authors)