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

Highlights: → Effective resonance energy E-barr is an essential nuclear parameter in the k0-NAA method. → For this, the cadmium ratio method was employed by dual monitors, 55Mn and 98Mo. → Then we have obtained experimentally the E-barr-values for 158Gd and 179Hf isotopes. → In this paper the available E-barr-values for both 158Gd and 179Hf isotopes are compared. - Abstract: The accuracy and precision of effective resonance energy E-barr 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-barr is an essential parameter, which is directly introduced in the k0-NAA standardization method. Therefore, the effective resonance energies E-barr 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 (Gth) and resonance neutron self-shielding (Gepi) for the irradiated samples, and self absorption (Fs) and true coincidence summing (Fcoi) effects for the measured γ-rays were taken into account. The experimental E-barr-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-barr-values of 158Gd and 179Hf were also theoretically calculated by using the recent resonance data in the literature. Since the experimentally determined E-barr-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-barr energies are thus compared with the present and earlier theoretical values, respectively. The presently measured E-barr value for 158Gd is generally larger than those obtained E-barr values from theoretical approaches by ∼9.1-16.9%. Whereas, the theoretically calculated E-barr-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.