First-Forbidden Beta-Decay Matrix Elements inTm170

Abstract

The directional correlation between once forbidden, nonunique 883-keV $\ensuremath{\beta}$ and the 84-keV $\ensuremath{\gamma}$ ray in the decay of $^{170}\mathrm{Tm}$ has been measured as a function of $\ensuremath{\beta}$ energy in the range 227 to 747 keV employing a fast-slow scintillation assembly. The attenuation of the correlation due to the finite lifetime of the intermediate state is determined by conducting an integral correlation experiment in both solid and liquid sources and is found to be about 30%. The present results on the directional correlation are combined with the nonallowed shape of the 883-keV $\ensuremath{\beta}$ transition for the extraction of the matrix-element parameters. The relative sizes of the matrix-element parameters show that a cancellation of rank-1 matrix elements may be responsible for the observed behavior of the 883-keV $\ensuremath{\beta}$ transition. The present matrix element parameters are consistent with the description of Woods-Saxon wave functions characterizing the states. The results on conserved-vector-current (CVC) ratio are in accordance with the ideas due to Damgaard and Winther. The CVC ratio ($\frac{1}{\ensuremath{\xi}}$) ($\frac{\ensuremath{\int}i\overline{\ensuremath{\alpha}}}{\ensuremath{\int}\overline{r}}$) is found to be $0.48\ensuremath{\le}(\frac{1}{\ensuremath{\xi}})\ifmmode\times\else\texttimes\fi{}(\frac{\ensuremath{\int}i\overline{\ensuremath{\alpha}}}{\ensuremath{\int}\overline{r}})\ensuremath{\le}0.81$, while the correction term $\ensuremath{\lambda}[=\frac{\ensuremath{\int}\overline{r}{(\frac{r}{R})}^{2}}{\ensuremath{\int}\overline{r}}]$ in CVC ratio due to Damgaard and Winther is established to be 2.3.