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

International audienceWe present recent results on the structure of the one-valence-particle Ca41 and Ca49 nuclei and the one-valence-hole Ca47 nucleus. The isotopes of interest were populated via the cold-neutron-capture reactions Ca40(n,γ), Ca48(n,γ), and Ca46(n,γ), respectively. The experiments were performed at the Institut Laue-Langevin, within the EXILL campaign, which employed a large array of high-purity germanium (HPGe) detectors. The γ decay and level schemes of these nuclei were investigated by γ-ray coincidence relationships, leading to the identification of 41, 10, and 6 new transitions in Ca41, Ca47, and Ca49, respectively. Branching ratios and intensities were extracted for the γ decay from each state, and γ-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 Ca41, Ca49, and Ca47 nuclei is characterized by the coexistence of either 2p-1h (two-particle–one-hole) and 1p-2h excitations, or couplings between single-particle or single-hole degrees of freedom and collective vibrations (phonons) of the doubly-magic “core.