Experimental determination of effective resonance energies for the (n,?) reactions of 71Ga, 75As, 115In, 152Sm, 158Gd, 164Dy, 170Er, 179Hf by dual monitor method

In this thesis, the main aim is to determine experimentally an average (effective) resonance energy replacing by all resonances lying in epithermal neutron spectra. To do this, a dual monitor (55Mn-98Mo) having favorable resonance properties is suggested. The effective resonance energy (Er) values for the 71Ga(n,?)72Ga, 75As(n,?)76As, 115In(n,?)116mIn, 152Sm(n,?)153Sm, 158Gd(n,?)159Gd, 164Dy(n,?)165Dy, 170Er(n,?)171Er and 179Hf(n,?)180mHf reactions were measured by using Cadmium ratios from a dual monitor (55Mn-98Mo). The powder samples were irradiated in an isotropic neutron field obtained from 241Am-Be neutron sources having an activity of 3x592 GBq. Thermal neutrons were shielded by using 1 mm thick Cd cylindrical box. Thus the induced activities in the samples were measured with a coaxial p-type HPGe detector with a relative efficiency of 120,8%. The necessary correction factors for gamma self-attenuation (Fg), thermal neutron self-shielding (Gth) and resonance neutron self-shielding (Gepi) effects were taken into account. To minimize the true coincidence summing (TCS) events due to possible X and ? ray summing effects, the very small samples were measured at a sample-detector distance of 10 cm. Also the Cd-ratios were determined by using the comparator technique, thus cancelling out the same magnitudes of TCS correction factors. The experimentally determined Er -values were 174±36 eV for 71Ga(n,?)72Ga, 112±23 eV for 75As(n,?)76As, 1,58±0,33 eV for 115In(n,?)116mIn, 8,65±1,80 eV for 152Sm(n,?)153Sm, 49,6±10,4 eV for 158Gd(n,?)159Gd, 225±47 eV for 164Dy(n,?)165Dy, 129±27 eV for 170Er(n,?)171Er and 17,0±3,5 for 179Hf(n,?)180mHf reactions, respectively. Since the experimentally determined Er -values for the 115In, 152Sm, 158Gd, 164Dy, 170Er and 179Hf isotopes are not available in literature, the present experimental results are compared only with those of the newest and earlier theoretically calculated ones. The present experimental results for the Er -values were also theoretically calculated by using the newest resonance data. The results show that the present experimental Er -values for the investigated isotopes agree within 0,6-15% with those of the theoretically calculated ones, except for 164Dy(n,?)165Dy. It is fonnd that the experimental Er -value 164Dy isotope shows a discrepancy varying between 0,4% and 35% from the calculated ones obtained by older and recent resonance data. In literature survey, a wide variation of the available Er -values implies the need for the new experimental determinations of Er -values for other isotopes to obtain more reliable and accurate analytical results. Because the Er -values, especially used in k0 standardization method can affect significiantly other analytical results obtained from a 1/E1+? distribution epithermal neutron spectra existing in real neutron fields