Spectroscopic Study of 63Ni via Cold Neutron Capture Reaction: I. Nuclear Structure of 63Ni

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The \gamma-radiation has been investigated for 63Ni produced by cold neutron capture in an enriched 62Ni sample. The 315 \gamma-rays produced were placed in a 63Ni level scheme, in which 272 placements are new. We determined the excitation energies with 0.2--0.8 keV error and the branching ratios of 62 bound levels in 63Ni, including 30 new levels. The Q-value of the 62Ni(n,\gamma)63Ni reaction amounts to 6837.75\pm 0.18 keV. A large-scale shell-model calculation was performed that included the four single-particle orbits of 0f_{7/2}, 1p_{3/2}, 0f_{5/2}, and 1p_{1/2}, assuming an inert 40Ca core for negative-parity states, and those of 1p_{3/2}, 0f_{5/2}, 1p_{1/2}, and 0g_{9/2}, assuming a 56Ni core for positive-parity states. The energies of the low-lying 63Ni states were successfully reproduced. A mean-field statistical-model calculation was also performed by using a self-consistent interaction between the Hartree--Fock + Bardeen--Cooper--Schrieffer method and the statistical calculation. The calculation result is consistent with the experimental level density of 63Ni.
2012-08-15