Experimental determination of the α-shape factor in the 1/E1+α epithermal-isotopic neutron source-spectrum by dual monitor method

The alpha-shape factor of real, non ideal 1/E1+alpha epithermal neutron spectrum in an isotropic neutron field of Am-241-Be isotopic neutron sources was determined by dual monitor method using measured cadmium ratios of Au-197(n,gamma)Au-198 and Mo-98(n,gamma)Mo-99(beta(-))Tc-99m reactions. The irradiations of Gold (Au) and Molybdenum (Mo), chosen as suitable monitors, were carried out with and without a 1 mm-Cd shield case. The induced activities in these monitors was measured by high resolution gamma-ray spectrometry with an n-type HPGe detector. The thermal neutron self-shielding effects in the monitor foils used in irradiations are negligibly small, however, the resonance neutron self-shielding effects were taken into account in the determinations. Thus, the obtained results for the alpha-shape factors for a real 1/E1+alpha epithermal-(241) Am-Be neutron source-spectrum at the four irradiation sites of the neutron irradiator are given and discussed. It is emphasized that the Au-197-Mo-98 isotopes can be chosen as suitable monitors in alpha-shape factor determination in real epithermal neutron spectra. (C) 2003 Elsevier Ltd. All rights reserved.