A Nanosecond Neutron Time-of-Flight Spectrometer Using Avalanche Transistors

A neutron time-of-flight spectrometer has been constructed and used to measure the energy of inelastically scattered 14.6-Mev neutrons. Neutrons were produced by the T(d, n) He4 reaction and flight time was measured using the associated particle method. Both neutrons and associated alpha particles were detected with plastic scintillators and photomultipliers. The transit time difference in the neutron photomultiplier was minimized with the aid of a nanosecond flash lamp that could be placed at various spots on the photocathode. Inexpensive avalanche transistors were used as time markers, pulse amplifiers, and in pulse-height discriminators to provide a "fast-fast" coincidence system. Time-of-flight was resolved (FWHM) to 0.95 and 1.6 nanoseconds with 20 percent and 86 percent energy windows, respectively, on the neutron detector.