Chemical stabilization of recoil ⁵⁶Mn in MnSO₄-KClO₄ mixed crystals following (n, γ) process

Abstract

Stabilization of recoil 56 Mn in mixed crystals of MnSO 4 -KClO 4 was studied with especial emphasis on isothermal annealing of neutron irradiated target. The results showed that * MnO 4 − yield (%) varies linearly with the increase in perchlorate concentration from 0.100 to 0.500 mol fraction, reaching a maximum value of (89.0 ± 1.1)%. However, the value of intercept (P 0 ) obtained was (63.0 ± 1.2)%. Isothermal annealing of 56 Mn in the present mixed crystal (MnSO 4 -KClO 4 ) of the two molar concentrations (i.e., 0.100 and 0.500 mol fraction) of perchlorate was studied at different temperatures for a desired length of time. The retention values increased with increasing temperature and time of annealing for both the samples. The values found for the two concentrations were (67.0 ± 1.0)% and (89.0 ± 1.1)%, respectively, at room temperature. Retention value increased gradually in the beginning but slowed down with a lapse of time and finally attained saturation within about 20 min of heating at 373 K in both cases. Limiting saturations were found to be (86.0 ± 1.0)% (max) for 0.100 molar concentration and (96.0 ± 0.8)% (max) for 0.500 molar concentration.The rate of annealing was found to increase while the extent of annealing decreased. The recoil re-entry process obeys first order rate law and the energies of activation for the system (MnSO 4 -KClO 4 ) computed from the classical Arrhenius plots were found to be 0.15 ± 0.05 eV for 0.1 molar ratio and (2.5 ± 0.06) × 10 −2 eV for 0.5 molar ratio. The low value of activation energy indicates that there is a recombination of recoil fragments and participation of defect controlled reactions in thermal annealing, leading to higher saturation retention in 0.500 molar ratio. The results obtained are discussed in the light of vacancies created by the dopant and helping in the proposed recoils stabilization mechanism.