High resolution measurements of neutron energy spectra from AmBe and AmB neutron sources

A 3He sandwich spectrometer incorporating two semiconductor detectors and a proportional counter region has been designed and constructed to perform high resolution measurements of neutron energy spectra in the energy range 100 keV to 15 MeV. The efficiency of the spectrometer was determined experimentally, using a 252Cf spontaneous fission source, in the low-scatter facility of the National Physical Laboratory. The Monte Carlo technique was also used to determine the efficiency and these calculated values were used to extrapolate the measured efficiency to higher energies. The neutron energy spectra from two different sized AmBe neutron sources and an AmB neutron source were measured. Although these spectra have been measured previously, the present work represents an improvement in the energy resolution and extends the energy range. Average values for dose equivalent quantities for neutrons from these sources are also presented. The spectral data is available from the authors, as a printed table or on a computer diskette, on request.