Fermi Strength Research Articles

β+Decay ofNa20

The decay scheme of $^{20}\mathrm{Na}$ has been studied in detail to obtain information on the $\ensuremath{\beta}$-decay mirror symmetry properties of the mass-20 multiplet and to determine the Fermi decay strength to the $T=1$ isobaric analog state in $^{20}\mathrm{Ne}$. The ratio $\frac{{\mathrm{ft}}^{+}}{{\mathrm{ft}}^{\ensuremath{-}}}$ was determined to be 1.026 \ifmmode\pm\else\textpm\fi{} 0.024 for the ${\ensuremath{\beta}}^{+}$ transitions to the first excited state of $^{20}\mathrm{Ne}$. The $\mathrm{ft}$ value for the transition to the $T=1, 10.278$-MeV level was measured to be 2992 \ifmmode\pm\else\textpm\fi{} 233 sec indicating that most of the Fermi strength is concentrated in this transition. A weak $\ensuremath{\gamma}$ transition from the ${2}^{+}$ isobaric analog state to the ${2}^{+}$ first excited state of $^{20}\mathrm{Ne}$ was observed and new ${\ensuremath{\beta}}^{+}$-delayed $\ensuremath{\alpha}$ groups are reported at 3.27, 5.272, and 5.701 MeV. Theoretical $\mathrm{ft}$ values derived from the shell-model wave functions are compared with experiment.

Concerning the anomalous Fermi strength in the β+-decay of 20Na and mirror symmetry in the mass-20 multiplet

The β +-strength in the decay of 20Na to the isobaric analog state in 20Ne has been measured precisely. Contrary to previous measurements, it has been found that essentially the full Fermi strength is associated with this transition. A test of mirror symmetry has also been made for the decay to the first excited state of 20Ne. There is evidence of an asymmetry somewhat smaller than that expected from the Wilkinson systematics.