GAS-TO-WALL ABSORBED DOSE CONVERSION FACTORS FOR NEUTRON ENERGIES OF 25 TO 250 MEV

Cavity chamber absorbed dose measurements do not usually strictly adhe re to the conditions of the Fano theorem and therefore the differences in the gas and wall mass stopping powers must be taken into account. Values of gas-to-wall absorbed dose conversion factors r(m,g) were cal culated for neutron energies of 25 to 250 MeV for detectors with walls of C, O, Mg, Al, Si, Fe, Zr, AlN, Al2O3, SiO2, ZrO2, and A-150 tissue -equivalent (TE) plastic and with gas cavities of acetylene, dry air, Ar, an Ar-CO2 mixture, CO2, isobutane, isobutane-based TE, methane, me thane-based TE, propane, and propane-based TE. The r(m,g) calculations required initial spectral fluences of H-1, H-2, H-3, He-3, and He-4 i ons released by neutron reactions in the walls, and these were calcula ted with Los Alamos High Energy Transport code. Mass-stopping-power da ta were taken from Ziegler and co-workers. Additional calculations wer e made in order to test the sensitivity of r(m,g) to input data from o ther sources, i.e., ion spectral fluences from the ALICE nuclear react ion code and mass-stopping powers from the recent ICRU evaluation. (C) 1997 Academic Press.