Decay ofP28

${}_{}{}^{28}{}_{}{}^{}\mathrm{P}$ has been formed in the ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}\mathrm{}(p,n)\mathrm{}{}_{}{}^{28}{}_{}{}^{}\mathrm{P}$ reaction at $E_p=16.5\mathrm{} \mathrm{and} 20$ MeV and its $\gamma$-ray spectrum was measured by means of two different target-transfer and Ge(Li) detector systems. $\gamma$-efficiency calibrations of the detectors were carried out with several radioactivity and neutron-capture $\gamma$-ray sources. Nine excited states of ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ up to 9382 keV are found to be populated in ${}_{}{}^{28}{}_{}{}^{}\mathrm{P}$ decay and the various positron and $\gamma$-ray branching ratios have been derived. The ${}_{}{}^{28}{}_{}{}^{}\mathrm{P}$ positron branch to the 1779-keV first excited state of ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ is ${68.4}_{-2.8\mathrm{}}^{+2.0\mathrm{}}$%. Comparison of this with the corresponding mirror ${\beta }^{-}$ decay of ${}_{}{}^{28}{}_{}{}^{}\mathrm{Al}$ gives $\frac{{\mathrm{}\left(\mathrm{ft}\right)\mathrm{}}^{+}}{{\mathrm{}\left(\mathrm{ft}\right)\mathrm{}}^{-}}={0.96}_{-0.03\mathrm{}}^{+0.04\mathrm{}}$ in striking disagreement with the results derived from earlier experimental data. The $\mathrm{ft}$ of (2.95 ± 0.23)× ${10}^3$ sec for ${}_{}{}^{28}{}_{}{}^{}\mathrm{P}$ ${\beta }^{+}$ decay to the ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ $T=1\mathrm{}$ analog state at 9316 keV agrees with that expected for a pure vector transition. A review is presented of mirror symmetry in even-$A$ systems with the conclusion that they do not reveal significant evidence for second class currents.