Delayed Neutron Measurements with a 3MV Dynamitron Accelerator

As part of a programme in neutron physics, the Birmingham Dynamitron accelerator is being used with deuterated or tritiated targets to produce neutrons of different energies which then stimulate fission in heavy elements. This paper describes energy measurements of delayed neutrons emitted after bursts of fissions in a 235U sample; a 3He spectrometer with a resolution (f.w.h.m.) of about 30keV for fast neutrons is being used to measure neutron energies. Electrostatic deflection in the top terminal of the accelerator gives 0.8s pulses of protons or deuterons every 1.8s; delayed neutrons are detected after a delay of 0.1s to allow the electronics to recover from each burst and the primary neutrons to die away. Simultaneous recording of the rise time and amplitude of the detector pulses gives a clear separation of events caused by 3He(n,p) reactions from others. Examples of delayed-neutron energy spectra are given for fission produced by primary neutrons of different energies up to 6MeV.