Absolute neutron fluence measurements between 0.5 and 3 MeV and their intercomparisons

Primary standards of monoenergetic neutron fluences for 0.565, 1.5 and 7.5 MeV neutrons produced by the Li-7(p,n)Be-7 reaction have been developed for the calibration of neutron dosimeters and spectrometers. The fluences for 0.565 MeV neutrons were measured using both H-2 and CH4 proton recoil propo rtional counters with the measured spectra fitted to the modified SPEC-4 Mo nte Carlo simulations for the subtraction of gamma and recoil carbons. The fluences for 1.5 and 7.5 MeV neutrons were determined with vacuum-type prot on recoil telescopes. Various uncertainties for each detector are analyzed and its overall uncertainty is 3.1% for gas counter and less than 3% for th e telescope. These neutron fluence standards have been intercompared with t hose of the National Physical Laboratory of the United Kingdom by the use o f two transfer instruments: a long counter and a He-3 detector. The compari son results will be presented and discussed. (C) 1999 Elsevier Science B.V. All rights reserved.