Fast Neutron Coincidence Spectrometer. II

A fast neutron coincidence spectrometer utilizing stilbene scintillators is described. The principle of the spectrometer is based upon the pulse-height analysis of the recoil protons resulting from a 45 degree scattering of the incident neutron beam. This is achieved by requiring the scattered neutron to be recorded in a secondary ring of ten stilbene scintillators. With delays corresponding to a fixed time of flight, a coincidence between the primary and secondary crystals gates the primary pulse. At 4 Mev the efficiency is of the order of 10−4 per incident neutron, and the pulse-height distribution has a width at half-maximum of 17%. The corresponding energy width is 10%. The time-of-flight characteristic is used to reject gamma rays. Limitations caused by accidentals and pulse-height resolution are discussed.