A "GREY " NEUTRON DETECTOR FOR THE INTERMEDIATE ENERGY REGION

A neutron detector for the accurate measurement of relative neutron flux intensities in the keV energy region is described. The detector consists, in its simplest arrangement, of a paraffin pile and a NaI(Tl) detector to detect the 2.2 MeV capture y-rays. The efficiency curve is relatively flat in the considered energy range. The efficiency curve depends only slightly on a change in the parameters used for its ca1culation. The application ofthe detector in neutron cross section experiments is described. that all neutrons are slowed down and captured in the moderator (no leakage). b. There should be no y-ray absorption in the sphere. With these assumptions and neglecting the capture in components of the moderator other than hydrogen, the 2.2-MeV y-ray flux integrated over the surface of the sphere is independent of the primary neutron energy of the source and equal to the neutron source strength. This means that the efficiency of the detector will be expected to be a constant. Due to this important basic principle of the detector, calculated efficiency curves taking into account the y-ray absorption in the sphere are very reliable as long as no neutron leakage occurs