Abstract
Abstract The interpretation of ion yields measured with ion chambers or proportional counters in terms of energy deposited depends on a precise knowledge of the W values, i.e. the mean energy expended to form an ion pair. Methane-base tissue-equivalent (TE) gas is widely used in neutron dosimetry. Neutrons ionise indirectly by induced charged particles. In tissue and TE material, recoil or reaction protons account for a major fraction of the energy deposited. This report presents a new analytical representation of proton-W values. New experimental results are included which strongly influence the analytical fit, as they have small measurement uncertainties and include W values for proton energies as low as 1 keV and as high as 3.46 MeV. The differences between the present and older evaluations as found in the literature are discussed. The new analytical fit includes a 'bump' in W values for proton energies at about 300 keV. The covariance matrix of the new model is studied and the influence of the new fit on Wn values and on microdosimetric spectra for neutrons is discussed.
Published Version
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