Low-spin particle/hole-core excitations in ${}^{41,47,49}$Ca isotopes studied by cold-neutron capture reactions

Abstract

We present recent results on the structure of the one-valence-particle ${}^{41}$Ca and ${}^{49}$Ca, and one-valence-hole ${}^{47}$Ca, nuclei. The isotopes of interest were populated via the cold-neutron capture reactions ${}^{40}$Ca(n,$\gamma$), ${}^{48}$Ca(n,$\gamma$) and ${}^{46}$Ca(n,$\gamma$), respectively. The experiments were performed at the Institut Laue-Langevin, within the EXILL campaign, which employed a large array of HPGe detectors. The $\gamma$ decay and level schemes of these nuclei were investigated by $\gamma$-ray coincidence relationships, leading to the identification of 41, 10, and 6 new transitions in ${}^{41}$Ca, ${}^{47}$Ca, and ${}^{49}$Ca, respectively. Branching ratios and intensities were extracted for the $\gamma$ decay from each state, and $\gamma$-ray angular correlations were performed to establish a number of transition multipolarities and mixing ratios, thus helping in the spin assignment of the states. The experimental findings are discussed along with microscopic, self-consistent beyond-mean-field calculations performed with the Hybrid Configuration Mixing model, based on a Skyrme SkX Hamiltonian. The latter suggests that a fraction of the low-spin states of the ${}^{41}$Ca, ${}^{49}$Ca, and ${}^{47}$Ca nuclei is characterized by the coexistence of either 2p-1h and 1p-2h excitations, or couplings between single-particle/hole degrees of freedom and collective vibrations (phonons) of the doubly-magic "core".

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