PARAMETERIZATION OF DETECTOR EFFICIENCY FOR THE STANDARDIZATION OF NAA WITH STABLE LOW FLUX REACTORS

With SLOWPOKE and MNS reactors which have reproducible neutron fluxes, the standardization of multielement NAA can be reduced to measuring a ctivation constants once for all elements and then determining relativ e detection efficiencies for new detectors and counting geometries. In this work a method has been developed for the parameterization of the efficiency of germanium detectors. The gamma-ray detection efficiency was measured as a function of energy and distance for three detectors . The variation with distance was found to follow a modified EID law, within 1%, for point sources 1 mm to 250 mm from the detector. A model , including coincidence summing corrections, was developed to calculat e efficiency for NAA samples; it requires 16 measured parameters. Test s showed that the calculated relative detection efficiencies are accur ate to better than 3% for close counting geometries and sample volumes up to a few millilitres. Areas of possible improvement to the accurac y of the method are suggested.