Experimental determination of effective resonance energies for 158Gd(n,γ) 159Gd and 179Hf(n,γ) 180mHf reactions

Abstract

The accuracy and precision of effective resonance energy E ¯ r parameter is an important point in the determination of the mass fraction of an analyte contained in the sample when NAA is used. Because the effective resonance energy E ¯ r is an essential parameter, which is directly introduced in the k 0–NAA standardization method. Therefore, the effective resonance energies E ¯ r for the 158Gd(n,γ) 159Gd and 179Hf(n,γ) 180mHf reactions were determined by cadmium ratio method using 55Mn and 98Mo monitors. The samples were irradiated in an isotropic neutron field of 241Am–Be neutron sources. The induced activities for the radioisotopes were produced in the samples with and without a 1 mm-thick Cd shield and then measured with a p-type high pure Ge detector. The correction factors required for thermal neutron self-shielding ( G th ) and resonance neutron self-shielding ( G epi ) for the irradiated samples, and self absorption ( F s ) and true coincidence summing ( F coi ) effects for the measured γ-rays were taken into account. The experimental E ¯ r -values are found to be 49.6 ± 10.4 eV for 158Gd and 17.0 ± 3.5 eV for 179Hf target isotopes, respectively. The E ¯ r -values of 158Gd and 179Hf were also theoretically calculated by using the recent resonance data in the literature. Since the experimentally determined E ¯ r -values for the 158Gd(n,γ) 159Gd and 179Hf(n,γ) 180mHf reactions are not available in literature, the present experimental results for the E ¯ r energies are thus compared with the present and earlier theoretical values, respectively. The presently measured E ¯ r value for 158Gd is generally larger than those obtained E ¯ r values from theoretical approaches by ∼9.1–16.9%. Whereas, the theoretically calculated E ¯ r -values for 179Hf isotope deviated substantially from the presently measured value by ∼16.9–37.6%. The reasons for this discrepancy are discussed in this paper.