Speaker
Description
Calcium nuclei between doubly closed shells, i.e. N=20 and N=28, offer a unique opportunity to investigate the evolution of nuclear structure from symmetric to neutron-rich systems. Along this isotopic chain, spherical configurations at shell closures are expected to be overcome by deformed structures in mid-shell nuclei, already at low excitation energy. This will significantly affect the interplay between single-particle and collective excitations, as well as particle/hole-core coupling schemes which appear in odd-mass isotopes. In this context, Ca nuclei lie in a mass region where different theoretical models, with different predictive powers, can be applied and turn out to be complementary to each other. This embraces ab initio approaches [1], shell-model calculations [2], DFT’s [3] and beyond-mean-field models [4-5].
In this work, we present recent results on the low-spin structure of $^{41-49}$Ca nuclei, populated in a series of (n,$\gamma$), neutron-capture experiments performed at Institut Laue-Langevin in Grenoble. These studies required the use of very rare target materials, such as $^{46}$Ca and $^{48}$Ca, as well as a radioactive $^{41}$Ca sample. High-resolution $\gamma$-ray spectroscopy was performed by using the high-efficiency EXILL [6-7] and FIPPS [8] HPGe composite arrays. Several new $\gamma$ rays were found, and level schemes were substantially extended up to the neutron-capture state, approaching a complete low-spin spectroscopy for these isotopes. Moreover, $\gamma$-ray angular correlations were performed in order to pin down the multipolarity of a number of transitions, thus helping in the spin-parity assignment of the observed states. A selection of the experimental results is discussed and compared with theoretical calculations, including those obtained with the Hybrid Configuration Mixing model recently developed by the Milano group [4,5,7].
[1] J. D. Holt et al., Phys. Rev. C 90, 024312 (2014).
[2] Y. Utsuno et al., Progr. Theor. Phys. Suppl. 196, 304 (2012).
[3] M. Bender et al., Rev. Mod. Phys. 75, 121 (2003).
[4] G. Colò et al., Phys. Rev. C 95 (2017) 034303.
[5] S. Bottoni et al., in preparation.
[6] M. Jentschel et al., J. Instrum. 12, 11003 (2017).
[7] S. Bottoni et al., Phys. Rev. C 103, 014320 (2020).
[8] C. Michelagnoli et al., EPJ Web of Conf. 193 04009 (2018).
