Abstract
Neutron rich nuclei around 48Ca have been measured with the CLARA–PRISMA setup, making use of 48Ca on 64Ni binary reactions, at 5.9 MeV/A. Angular distributions of γ rays give evidence, in several transfer channels, for a large spin alignment (≈70%) perpendicular to the reaction plane, making it possible to firmly establish spin and parities of the excited states. In the case of 49Ca, states arising from different types of particle–core couplings are, for the first time, unambiguously identified on basis of angular distribution, polarization and lifetime measurements. Shell model and particle–vibration coupling calculations are used to pin down the nature of the states. Evidence is found for the presence, in the same excitation energy region, of two types of coupled states, i.e. single particle coupled to either 48Ca or 50Ca simple configurations, and particle–vibration coupled states based on the 3− phonon of 48Ca.
Highlights
48Ca on 64Ni binary reactions, at 5.9 MeV/A
Evidence is found for the presence, in the same excitation energy region, of two types of coupled states, i.e. single particle coupled to either 48Ca or 50Ca simple configurations, and particle–vibration coupled states based on the 3− phonon of 48Ca
It is interesting to verify if these properties manifest themselves in adjacent nuclei, such as 49Ca, where states have been attributed to the coupling of core excitations with a single particle, either starting from 48Ca or 50Ca [14]
Summary
For the first time with heavy-ion transfer reactions, we clearly show the possibility of using angular distributions and polarization of the γ transitions to firmly establish spin and parity of the nuclear states. While the 3.589- and 4.017-MeV states were interpreted as J π = 5/2− and 9/2+ state (with large uncertainty due to the limited energy resolution of the detected particles), the state at 3.357 MeV showed a very anomalous angular distribution of the scattered proton, leading to a questionable assignment ( J π = 9/2+) These states were never unambiguously identified even in more recent γ -spectroscopy studies [18] (e.g. by measuring the character and multipolarity of the transitions involved). We describe the 9/2+ state of 49Ca by applying a particle–vibration weak coupling scheme [1], while we make use of shell model calculations to interpret the nature of the 7/2− state
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