Measurement of Neutron Kerma Factors in C and O: Neutron Energy Range of 20 MeV to 70 MeV

Kerma factors for oxygen and carbon have been measured in nearly monoenergetic neutron beams of energies between 34 MeV and 66 MeV. The kerma was determined experimentally with low pressure proportional counters (PC) by measuring the absorbed doses to the gases. Recently calculated gas-to-wall absorbed dose conversion factors, rm.g, were used to deduce the doses in the PC wall materials. The kerma in oxygen was obtained from the difference of the kerma determined with ZrO2 and Zr walled PCs, that in carbon was determined with graphite-walled PCs. The neutron fluences were measured with a proton recoil telescope, the spectral fluences with an NE213 scintillation detector by applying pulse shape and time-of-flight techniques. The kerma factors of carbon from the present measurements were compared with values of previous works which were analysed anew using the improved rm.g values.