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Determination of d(3)-Be and d(4)-Be neutron spectra using a recoil proton spectrometer

At the Gray Laboratory a 4 MV van de Graaff accelerator is used to produce neutrons for radiobiology research by bombarding a thick beryllium target with deuterons. Several of the parameters used in neutron dosimetry are dependent upon the neutron energy spectrum. This has prompted the construction of a recoil proton spectrometer which uses a high-resolution silicon surface barrier detector to measure the energy of protons scattered from a thin polypropylene radiator by the neutron beam. Because of the high-scatter environment within the neutron room, fast coincidence methods have been employed to reject spurious pulses. The coincidence signal is derived from a proportional counter located between the silicon and the radiator. By making the radiator as thin as practicable, it has been possible to reduce the lower energy detection threshold to 600 keV. Results are presented for the d(4)-Be spectrum at 0 and 9 degrees to the deuteron beam axis and the d(3)-Be spectrum at 9 degrees . The energy calibration and response have been checked by measuring near-monoenergetic neutrons from th d(4)-D reaction.