4He detectors for Mixed Oxide (MOX) fuel measurements

A neutron spectroscopic technique for plutonium content measurement is described. The technique exploits the kinematic cutoff of neutron emission in (α,n) reactions on oxygen. The Watt spectrum of fission neutron emission extends to higher energies without such a cutoff. 4He scintillation detectors were calibrated with an energy cut to reject neutrons of low energies, thereby making the detectors sensitive only to fission neutrons but not to neutrons from the (a,n) reaction on oxygen