Evidence for Rotational Structure at High Spins inEr154,155

Abstract

Erbium nuclei around $N=86\mathrm{}$, which are weakly collective at spins below about $40\hslash$, have been studied at higher spin using techniques recently developed for studying continuum $\gamma$ rays. A strong collective structure appears to develop above spins around $40\hslash$, which can expalin why no discrete lines have been observed beyond $36\hslash$. The similarity of the spectra for heavier and lighter erbium nuclei at spins $\mathrm{}(40-60)\mathrm{}\hslash$ suggests the same shape (prolate) for both.