Time of Flight Spectrometer for Fast Neutrons

A fast neutron spectrometer, using the time of flight method, which may also be used to study reactions involving the simultaneous emission of neutrons and gamma rays, is described. One stilbene scintillation counter is placed close to the source, the other a suitable distance away. The two are connected to a new type of coincidence time sorter which converts delay time between associated events into a pulse amplitude distribution which may be analyzed by a kicksorter, so enabling the whole range of delay times or energies to be displayed and recorded at one time. The delay time may result from neutron flight time following scattering in the first counter, from the time of flight of a neutron from the target associated with a gamma ray entering the first counter, or from a charged particle associated with a gamma ray. Using D(d,n)He3 neutrons and a flight path of 50 cm, it has been possible to measure the energy with an accuracy of 10%. Angular correlations arising from (−,nγ) reactions may be studied with energy discrimination of the neutrons; typical results are presented for the case Be9(d,nγ)B10.