Determination of effective resonance energies for the $^{185}$Re(n,$\gamma )^{186}$Re and $^{187}$Re(n,$\gamma )^{188}$Re reactions by cadmium ratio method


Abstract: The effective resonance energy ($\bar{E}_{r})$ values for the $^{185}$Re(n,$\gamma )^{186}$Re and $^{187}$Re(n,$\gamma )^{188}$Re reactions were measured by using the cadmium ratio method. $^{197}$Au and $^{98}$Mo isotopes were selected as dual monitors to determine the epithermal neutron spectrum shape factor in the irradiation sites of a 37 GBq $^{241}$Am-Be neutron source. The analytical grade rhenium(VII) oxide samples were diluted with Al$_{2}$O$_{3}$ powder to reduce neutron self-shielding effects, and they were put into 1-mm thick small cylindrical polytetrafluoroethylene (PTFE) boxes. Samples were irradiated in a $^{241}$Am-Be neutron source. The activation produced in the irradiated samples was measured in close-counting geometry on the end cap of a Ge detector in order to obtain better counting statistics. The correction factors for gamma-ray self-absorption ($F_{s})$, thermal neutron self-shielding ($G_{th})$, and epithermal neutron self-shielding ($G_{epi})$ effects were determined with suitable approaches. Consequently, the experimental $\bar{E}_{r}$-values were measured to be 3.49 ± 0.54 eV for $^{185}$Re and 41.77 ± 6.79 eV for $^{187}$Re target nuclide, respectively. Furthermore, the $\bar{E}_{r}$-values were theoretically computed through up-to-date resonance data obtained from the ENDF/B VII library using two different approaches. Since there is no experimental data available in the literature for the $\bar{E}_{r}$-values of these isotopes, the results were compared with the theoretical values in the literature.

Keywords: Effective resonance energy, neutron activation, cadmium ratio, epithermal spectrum shape factor, rhenium

Full Text: PDF