Lowest2+State inGd8264146and the Energy Gap atZ=64

Abstract

A search for the lowest $2^{+}$ state in ${}_{}{}^{146}{}_{}{}^{}\mathrm{Gd}$ using ($\alpha$,$2n\gamma$) excitation function measurements near threshold has located that state at 1971 keV. Its energy, more that 300 keV higher than in any other $N=82\mathrm{}$ nucleus, provides clear spectroscopic evidence for a large gap in the single-particle spectrum at $Z=64\mathrm{}$.