Fast neutron beam dosimetry: comparison of the ion chamber and proportional counter approaches

Data were presented comparing the absorbed dose in tissue exposed to beams of fast neutrons as measured by ion chambers and tissue-equivalent proportional counters. The fast neutron beams studied include 14 MeV monoenergetic beams and those generated by high energy deuterons incident on beryllium. The ion chamber approaches include the tissue-equivalent plastic, tissue-equivalent gas and polyethylene wall-ethylene gas systems. The proportional counters were of the tissue-equivalent wall-tissue-equivalent gas type. Sources of uncertainty were discussed, including values of stopping power ratios, W for the gases, differences in atomic composition between the wall and the gases, and separation of the photon component of the total dose.