Low energy component of the spectra of fast neutron beams in clinical use

A fast neutron spectrometer based on an NE 213 liquid scintillator cell has been developed. For good spatial resolution within a water phantom, the cylindrical scintillator is small (1.5 cm diameter*1.5 cm length). Discrimination between neutron and gamma-ray induced ionisation events in the scintillator is effected on the basis of scintillation pulse shape. Some preliminary measurements of the fast neutron spectrum of a 10 Ci 238Pu-Be isotopic neutron source are presented.