A novel application of the high-pressure ionisation chamber to measure the mean neutron energy or the gamma ray dose fraction in a mixed neutron-gamma radiation field

A novel application of the tissue-equivalent ionisation chamber operated at high pressures of 8 atm (1 atm = 101 325 Pa) is presented to measure the mean incident neutron energy or gamma ray absorbed dose fraction of an unspecified neutron-gamma radiation field in the neutron energy region 0.1-10 MeV. The method is based on initial recombination in high-pressure ionisation chambers irradiated by neutrons and gamma rays simultaneously. The concept of a 'spectrum-equivalent electron' which was introduced in a previous paper describing recombination of charge carriers produced by gamma rays is generalised here to included recombination of charge carriers in neutron recoil tracks (protons, alpha particles and heavy ions) produced in tissue-equivalent plastic. Empirical relations are then established between the recombination quantities, the mean incident neutron energy and the gamma ray absorbed dose fraction for neutrons in the energy range 0.1-10 MeV. The estimated total uncertainties in the mean neutron energy and gamma ray dose fraction are of the order of 10%. (author)