KERMA MEASUREMENTS IN POLYENERGETIC NEUTRON FIELDS

Absorbed dose was measured as a function of neutron energy with a smal l spherical proportional counter (PC) irradiated in the pulsed-beam br oad energy spectrum neutron fields of the Physikalisch-Technische Bund esanstalt (PTB) that were produced with the p + Be reaction and extend ed to 20 MeV neutron energy. Time-of-flight (TOF) discrimination metho ds augmented the traditional microdosimetric pulse height (PH) analysi s and yielded absorbed dose as a function of lineal energy y and neutr on TOF. Below 0.7 keV.mu m(-1) lineal energy, unfolding procedures gre atly improve the time resolution, e.g. from 225 ns full width at half maximum (FWHM) to 65 ns FWHM at 1.2 keV.mu m(-1). The overall time res olution from unfolded TOF spectra is approximately 30 ns FWHM. The abs orbed dose was normalised to neutron spectral fluence and, on the assu mption that kerma is numerically equal to absorbed dose, yielded relat ive neutron fluence-to-kerma conversion coefficients as a function of energy that are in good agreement with values from previous work.