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 2.5 MeV neutrons produced by the 7Li(p,n)7Be reaction have been developed for the calibration of neutron dosimeters and spectrometers. The fluences for 0.565 MeV neutrons were measured using both H2 and CH4 proton recoil proportional counters with the measured spectra fitted to the modified SPEC-4 Monte Carlo simulations for the subtraction of gamma and recoil carbons. The fluences for 1.5 and 2.5 MeV neutrons were determined with vacuum-type proton recoil telescopes. Various uncertainties for each detector are analyzed and its overall uncertainty is 3.1% for gas counter and less than 3% for the telescope. These neutron fluence standards have been intercompared with those of the National Physical Laboratory of the United Kingdom by the use of two transfer instruments: a long counter and a 3He detector. The comparison results will be presented and discussed.