Study of the Gamma Rays from Thermal-Neutron Capture inNi64

The $\gamma$ radiation emitted following thermal-neutron capture in ${\mathrm{Ni}}^{64}$ has been studied in singles and coincidence with 15-, 30-, and 40-${\mathrm{cm}}^3$ Ge(Li) detectors. $\gamma$ rays of the following energies (in keV) and relative intensities (in parentheses) were assigned to ${\mathrm{Ni}}^{65}$: 63.6 (13), 247.1 (0.5), 310.5 (23.0), 382.0 (0.7), 628.8 (7.3), 692.2 (1.5), [726 (0.2)], 1107.4 (3.8), [1418 (0.2)], 2083.8 (0.6), 2147.2 (0.3), 3950.2 (1.1), 4679.5 (3.8), 5405.2 (9.2), 5787.1 (18), 6034.0 (70). All these transitions were incorporated in a level scheme for the ${\mathrm{Ni}}^{65}$ nucleus with levels at the following energies: 63.6 ± 0.3, 310.5 ± 0.2, 692.3 ± 0.3, 1417.9 ± 0.4, and 2147.2 ± 0.5 keV. A lower lifetime limit of $\tau >3\mathrm{}$ μsec was measured and a conversion coefficient $\alpha \sim 5$ deduced for the 63.5-keV state. These are consistent with the ${\frac{1}{2}}^{-}$ assignment made in a study of the ${\mathrm{Ni}}^{64}\mathrm{}(d,p)\mathrm{}{\mathrm{Ni}}^{65}$ reaction. A ${\frac{3}{2}}^{-}$ assignment is suggested for the 310.5-keV state by the branching ratio to the 63.6-keV level and the ground state. The neutron separation energy is 6097.6 ± 0.6 keV for ${\mathrm{Ni}}^{65}$ and 6837.6 ± 1.0 keV for ${\mathrm{Ni}}^{63}$. The strengths of the five observed primary transitions and corresponding proton groups in the ($d,p$) reaction have been compared and a correlation co-efficient of 0.8 obtained. The $\gamma$ decay of the ${\mathrm{Ni}}^{65}$ ground state was also investigated.