Calculation of recoil-order matrix elements for the beta decays ofF20andNa20.

The matrix elements which affect the shapes of the $\beta$ spectra and the $\beta -\gamma$ angular correlations are calculated for the ${}_{}{}^{20}{}_{}{}^{}\mathrm{F}$-${}_{}{}^{20}{}_{}{}^{}\mathrm{Na}$ mirror Gamow-Teller decays to the 1634 keV level of ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$. The dominant effects are due to the weak-magnetism and the axial-vector tensor form factors. Matrix elements relevant to the $\beta -\alpha$ correlations for other ${}_{}{}^{20}{}_{}{}^{}\mathrm{Na}$ decays are also evaluated, with similar conclusions.