Meson-exchange enhancement of the first-forbiddenYg96(0−)→96Zrg(0+)βtransition:βdecay of the low-spin isomer ofY96

We have investigated the $0^{\mathrm{-}}$ ${}_{}{}^{96}{}_{}{}^{}\mathrm{Y}_{}^{\mathrm{g}}{}_{}{}^{}$ β decay to the levels of ${}_{}{}^{96}{}_{}{}^{}\mathrm{Zr}$. A detailed decay scheme comprised of 63 γ rays and 44 energy levels has been obtained from γ singles, γ multispectral scaling, and γ-γ and E0-γ coincidences. $Q_{\beta }$ was measured using the β-γ coincidence technique, while absolute E0 and γ-ray intensities were obtained from singles conversion electron and γ-ray spectra measured at beam saturation. The high sensitivity of the study was aimed at investigating the β feeding of levels with excitation enegy above 4 MeV. Although most of the new levels were found in this region, their total β feeding was found to be below 0.6%. The first-forbidden β-decay rate for $0^{\mathrm{-}}$ ${}_{}{}^{96}{}_{}{}^{}\mathrm{Y}_{}^{\mathrm{g}}{}_{}{}^{}$→$0^{+}$ ${}_{}{}^{96}{}_{}{}^{}\mathrm{Zr}_{}^{\mathrm{g}}{}_{}{}^{}$ has been calculated within the framework of the spherical shell model using a model space of π(0${\mathit{f}}_{7/2}$,0${\mathit{f}}_{5/2}$,1${\mathit{p}}_{3/2}$,1${\mathit{p}}_{1/2}$,0${\mathit{g}}_{9/2}$) 1${\mathit{p}}_{1/2}$,0${\mathit{g}}_{9/2}$)ν (${0\mathrm{g}}_{7/2}$,1${\mathit{d}}_{5/2}$,1${\mathit{d}}_{3/2}$,2${\mathit{s}}_{1/2}$) with limitations on the orbit occupancies. Additional evidence for meson enhancement of the timelike component of the axial current is obtained; the meson-exchange enhancement factor was found to be 1.75±0.30, where the uncertainty arises from the calculation.