High-spin levels in137,139Ce and139,141Nd evidence for hole-core coupling

Abstract

Excited states of the137Ce,139Ce,139Nd and141Nd nuclei have been studied using the138Ba(α, 5nγ)137Ce,138Ba(3He, 4nγ)137Ce,138Ba(α, 3nγ)139Ce,140Ce(α, 5nγ)139Nd,140Ce(3He,4nγ)139Nd,140Ce(α, 3nγ)141Nd and142Ce(α, 5nγ)141Nd reactions. Singlesγ-ray spectra,γ —γ coincidence spectra, angular distributions and time distributions ofγ-rays with respect to beam pulses have been measured. Gamma transitions between excited states with spin values up to 21/2, 23/2 or 25/2 have been observed. Isomeric states with T1/2=70 ns have been observed in139Ce at 2631.5 keV (19/2) and in141Nd probably at 2952.0 keV (19/2). The level structure observed in the nuclei studied can be explained if the neutron-holes are coupled to the doubly even core excitations. The coupling of theh 11/2 neutron-hole with the 2+, 4+ and 3− collective excitations are calculated in terms of the weak and intermediate coupling models. The intermediate coupling results seem to be in better agreement with the experimental data. The energies of theree-particle states, being the result of the coupling of theh 11/2 neutron-hole with the two-proton excitations in the core, are well reproduced in the calculations when empirical values of the two-body interaction matrix elements were used.