A monoenergetic neutron beam facility for biological irradiations

Abstract

This paper describes in detail the calibration methods and utilisation of a fast neutron source for biological irradiations, which is relatively free from gamma ray contamination. The project arose from the need for biologists to have access to a source of high energy neutrons (>1 MeV) for comparison of data with that already obtained using lower LET sources such as X-rays and γ-rays. This Standard Neutron Irradiation Facility (SNIF) was set up on a 3 MV Van de Graaf accelerator and produced well characterised monoenergetic beams of 3 to 6 MeV neutrons using the 2D(d,n) 3He nuclear reaction. Full width neutron energy spreads of 200 keV for 5.4 MeV neutrons were readily obtainable as were fluxes up to 6×10 8 n/cm 2 s producing dose rates up to 100 Gy/h. The γ-ray contamination was estimated to be less than 5% for most neutron irradiations. The major limitation to the maximum dose rates attainable was the maximum power dissipation in the thin Havar window separating the pressurised cell deuterium gas from the evacuated beamline.