Test of recoil spectrometer by measurement of the neutron spectrum of a polonlium-beryllim neutron source
A proton-recoil neutron spectrometer for use with the Cockroft-Walton neutron generator now under construction was designed, built, and used to measure the spectrum of a 0.3 curie polonium-beryllium neutron source as a test of operation. In this device, protons recoiling from a thin polyethylene radiator foil at less than the maximum accepted angle with the neutron pass through a proportional counter where energy loss rate is measured and strike a thin CsI(Tl) crystal mounted on a DuMont 6292 Photomultiplier tube. The resulting pulse, which is a measure of the energy of the proton, passes through a gate circuit into a single-channel analyzer. This gate opens only when the signal pulse is in coincidence with a proportional counter pulse of proper size to identify the particle as a proton. The original energy of the neutron can then be calculated from knowledge of the proton spectrum and the average energy losses in radiator, proportional counter, and n-p scattering. Except for a considerable excess of observed low energy particles believed to be caused by neutron scattering in the brass wall opposite the radiator, the agreement with the known spectrum was generally within the 16% average uncertainty. Suggestions are made for improving this performance.