Kerma Measurements in Polyenergetic Neutron Fields

Abstract

Absorbed dose was measured as a function of neutron energy with a small spherical proportional counter (PC) irradiated in the pulsed-beam broad energy spectrum neutron fields of the Physikalisch-Technische Bundesanstalt (PTB) that were produced with the p + Be reaction and extended to 20 MeV neutron energy. Time-of-flight (TOF) discrimination methods augmented the traditional microdosimetric pulse height (PH) analysis and yielded absorbed dose as a function of lineal energy y and neutron TOF. Below 0.7 keV.μm -1 lineal energy, unfolding procedures greatly improve the time resolution, e.g. from 225 ns full width at half maximum (FWHM) to 65 ns FWHM at 1.2 KeV.μm -1 . The overall time resolution from unfolded TOF spectra is approximately 30 ns FWHM. The absorbed dose was normalised to neutron spectral fluence and, on the assumption that kerma is numerically equal to absorbed dose, yielded relative neutron fluence-to-kerma conversion coefficients as a function of energy that are in good agreement with values from previous work.