Transitional Nuclei. II. Properties of the Levels in 152Sm and 152Gd from the Decay of the 152Eum,g Isomeric Pair

Abstract

The γ rays emitted in the decay of the 152Eum,g isomeric pair have been studied with the use of high-efficiency, high-resolution, solid-state detectors. These measurements together with Ge(Li)–Ge(Li) coincidence experiments revealed the existence of several new gamma transitions never previously reported. In all, 93 and 30 γ rays were observed in the decay of 152Eug and 152Eum, respectively. Calculations of the β- and γ-band mixing into the ground-state rotational band and into each other were carried out. These calculations showed that this mixing is insufficient in explaining the B(E2) ratios from the members of both the β and γ band. In addition, the very likely existence of a Kπ = 2− band in 152Sm, with levels at 1649.90 (2−) and 1757.0 keV (3−), has been unveiled in these measurements. Furthermore, the existence of a new Kπ = 0− octupole rotational band (levels at 1680.58 (1−) and 1730.3 (3−)) built on the β-vibrational band and the presence of a collective Kπ = 2+ vibrational state at 1769.1 keV, which most probably can be described as a coupled (βγ) two phonon state, are also proposed. Moreover, a new level at 1292.75 keV has been established through coincidence experiments in 152Sm. This level may be considered either as the 2+ member of a second β-vibrational band or, more likely, can be described as a truly spherical state in light of recent experiments involving (t,p) and (p,t) transfer reactions to levels of 152Sm. Finally, a qualitative analysis of the level structure of 152Gd, as well as 150Sm, seems to show that these two nuclei display a more rotational nature than a spherical (or vibrational) one as previously suggested.