The Application of a Neutron Identification Circuit to the Study of Fast-Neutron Interactions in Stilbene

A neutron identification circuit is described which has a threshold corresponding to a neutron energy of about 350 kev (50–60 kev equivalent electron energy). The photomultiplier is operated under conditions of space-charge saturation. Selection of pulses due to recoil protons or heavier particles is accomplished by allowing the initial negative-going spike of the space-charge-limited pulse from the last dynode to activate a trigger circuit, the output of which is used to gate the subsequent positive portion of the dynode pulse for presentation to a simple diode discriminator. Separation of pulses due to recoil protons and to α particles is also possible to some extent.The circuit is applied to an investigation of fast-neutron interactions in stilbene. For the case of 14.85-Mev neutrons it is shown that the majority of pulses of low light-output are due to α particles produced by neutron interactions with the carbon and that structure is apparent in this α-particle spectrum. α-Particle groups due to the C 12 (n, α)Be 9 reaction and to the breakup of C 12 from its excited states at 7.656 Mev and 9.63 or 10.1 Mev are identified.