The decay scheme of ${}_{}{}^{20}{}_{}{}^{}\mathrm{Na}$ has been studied in detail to obtain information on the $\beta$-decay mirror symmetry properties of the mass-20 multiplet and to determine the Fermi decay strength to the $T=1\mathrm{}$ isobaric analog state in ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$. The ratio $\frac{{\mathrm{ft}}^{+}}{{\mathrm{ft}}^{-}}$ was determined to be 1.026 ± 0.024 for the ${\beta }^{+}$ 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 ± 233 sec indicating that most of the Fermi strength is concentrated in this transition. A weak $\gamma$ transition from the $2^{+}$ isobaric analog state to the $2^{+}$ first excited state of ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ was observed and new ${\beta }^{+}$-delayed $\alpha$ 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.

• Received 22 January 1973

DOI:https://doi.org/10.1103/PhysRevC.8.161