High-spin states and evidence for particle-core coupling in the N = 83 isotones: ¹⁴³Nd, ¹⁴⁵Sm and ¹⁴⁷Gd

Abstract

The level structure of the ¹⁴³Nd, ¹⁴⁵Sm and ¹⁴⁷Gd nuclei has been studied using the ${}^{142}\text{Ce}\text{(α, 3}\text{n}\text{γ)}{}^{143}\text{Nd}\text{,}{}^{144}\text{Nd}\text{(α, 3}\text{n}\text{γ)}{}^{145}\text{Sm}$ and ¹⁴⁴Sm(α, nγ)¹⁴⁷Gd reactions. Singles γ-ray, γ-γ coincidence spectra, angular and time distributions with respect to the beam bursts have been measured at various bombarding energies. Gamma transitions between excited states with spin values up to $\text{25}\text{2}$⁺ have been observed in all the nuclei investigated. The lifetime and angular distribution measurements performed confirm the recently proposed reassignment of some low-lying high-spin states in the N = 83 isotones considered as $\text{13}\text{2}$⁺ excitations. The observed level structure in these N = 83 nuclei can be explained if the extra neutron outside the N = 82 closed shell is coupled to doubly even core excitations. The coupling of the neutron single particle excitations (mainly in the 2f_{$\text{7}\text{2}$}, 1h_{$\text{9}\text{2}$} and li_{$\text{13}\text{2}$} orbitals) to the lowest 2⁺ and 3⁻ vibrations of the core is calculated within the framework of an intermediate coupling model. The results obtained in these calculations are in good agreement with the experimental data. The energies of the three-particle states, being the results of the coupling of the 2f_{$\text{7}\text{2}$} or the 1i_{$\text{13}\text{2}$} extra neutron to two-proton excitations in the core, are nicely reproduced in the calculations, when empirical values of the two-body interaction matrix elements are used.