Lifetime of the 31- state and octupole collectivity in 96Zr.

The half-life of the 1897.2-keV, 3[sub 1][sup [minus]] state in [sup 96]Zr has been measured as (67.8[plus minus]4.3) ps using the recoil-distance technique following inelastic excitation by 105-MeV [sup 32]S ions. This is equivalent to a lifetime which is about 40% longer than those reported from two recent centroid-shift measurements. Our lifetime implies [ital B]([ital E]3)[up arrow]=(0.180[plus minus]0.018) [ital e][sup 2]b[sup 3], i.e., (47.1[plus minus]4.7) W.u., which is the most enhanced one-phonon g.s.[r arrow]3[sub 1][sup [minus]] transition strength observed in nuclei. A recent quasiparticle random-phase approximation (QRPA) calculation reproduces our result. Serious doubts are raised about an earlier conclusion that the reduced octupole transition probabilities of mirror'' nuclei correspond to the harmonic low for small amplitude vibrations. The enhanced [ital B]([ital E]1:3[sub 1][sup [minus]][r arrow]2[sub 1][sup +])=(1.71[plus minus]0.11) 10[sup [minus]5] [ital e2]b deduced from the present work is consistent with appreciable octupole deformation. The measured [ital B]([ital E]3)[up arrow] resolves problems in the interpretation of the isospin character of the [ital E]3 transition derived from inelastic scattering data.