Search for Shape Coexistence in Ca Isotopes by (\(n_\mathrm {th}\),\(\gamma \)) Reactions

The \(A\sim 40\) mass region is ideal to study the evolution of nuclear structure and to probe different theoretical approaches. In particular, in these nuclei, phenomena like shape coexistence are expected to appear. The objective of this work is to study the evolution of such phenomena across the Ca isotopic chain by performing complete low-spin spectroscopy of even–even \(^{42,44}\)Ca and odd–even \(^{43,45}\)Ca isotopes and, together with the already published results on \(^{41,47,49}\)Ca, track the evolution of nuclear structure along \(Z=20\). All four isotopes relevant to this work were populated by (\(n_\mathrm {th}\),\(\gamma \)) neutron-capture reactions exploiting thermal neutrons from the ILL (Grenoble) nuclear reactor. In this article, we present preliminary results on \(^{42}\)Ca and \(^{44}\)Ca. In our experiments, we used the FIPPS spectrometer to detect \(\gamma \)-rays, and both double-\(\gamma \)- and triple-\(\gamma \)-coincidence techniques were used to reconstruct the decay schemes. The result is 10 new levels and 109 new transitions for \(^{42}\)Ca, and 27 new levels and 280 new \(\gamma \) rays in \(^{44}\)Ca. Preliminary angular correlation studies of \(^{42}\)Ca excited states will also be presented, and the population of \(0^+\) excited states, possibly associated with shape coexistence, will be discussed. Abstract Published by the Jagiellonian University 2026 authors