A COMBINATION NEUTRON AND GAMMA RAY SPECTROMETER

An instrument has been developed to measure neutron and gamma ray spectra simultaneously in a mixed radiation field. The method utilizes a single stilbene scintillation crystal with a pulse-shape discrimination cricuit. The system routes pulses due to electrons to one output and those due to protons to another output. The spectra are then independently accumulated and analyzed. The response of the spectrometer to neutrons and gamma rays is included. The gamma ray efficiency of the stilbene crystal (1 1 2 o {combining double acute accent} dia. × 1 1 2 o {combining double acute accent} high) varied from approximately 20% at 1 MeV down to 7% at 10 MeV (counts per incident particle). The gamma ray resolution of the complete spectrometer system, including unfolding, is 31% at 0.322 MeV and 14% at 1.84 MeV. The neutron efficiency of the crystal varied from approximately 48% at 1 MeV down to 13% at 10 MeV (counts per incident particle). The neutron resolution of the spectrometer is 17.4% at 2.0 MeV and 5.2% at 15.5 MeV. Measured neutron and gamma ray spectra from a PuBe neutron source are presented. The total neutron output of the source, measured by the National Bureau of Standards, is 1.00 × 107 n/sec. The output measured with the stilbene spectrometer is 1.09 × 107 n/sec. The agreement is within 10%. © 1968.