Breakdown of vibrational structure in Ru-98

Abstract

The nucleus Ru-98, the lightest collective Ru isotope with N>50, has been studied employing the (alpha,2n) reaction using YRAST Ball detectors. The new data, as well as a systematic set of limits on the intensities of unobserved transitions, reveal a structure that resembles a near harmonic vibrator spectrum up through the two-phonon triplet but show an almost complete breakdown of vibrator structure thereafter. These results are not understood theoretically and are at variance with previous interpretations of this nucleus. A rare anomaly in yrast B(E2) values is also pointed out.