The calibration of neutron instruments and dosimeters at intermediate energies

A system of Bonner spheres, a Harwell Type 95/0075 neutron survey meter, an albedo dosimeter and a 237Np fission-foil dosimeter have been calibrated using a bare antimony-beryllium (Sb-Be) source emitting neutrons principally at 23 keV, and a moderated Sb-Be source emitting a broad spectrum of neutrons centred on 0.5 keV. Special techniques and precautions were employed to overcome problems associated with the large gamma-ray emission from the sources. The responses of the Bonner spheres were found to be in reasonable agreement with some published response curves and in poor agreement with others. The 0075 survey meter was found to over-read by a factor of about three for both sources (compared with the newer ICRP conversion function). The measurements confirmed that the albedo dosimeter has a response proportional to dose-equivalent over much of the intermediate-energy range and that the 237Np fission-foil dosimeter in free-air shows appreciable sensitivity to 0.5 keV neutrons and a low sensitivity at 23 keV, consistent with published cross-sections. The presence of a phantom was shown to modify significantly the response of this dosimeter. (Auth.)