The beta- and gamma-rays occurring in the decay of ${\mathrm{Al}}^{28}$ have been measured by means of lens spectrometers using sources activated by the ($n,\gamma$) and ($d,p$) reactions on aluminum. The gamma-ray has an energy of 1.782±0.010 Mev and the beta-ray end point is found to be 2.865±0.010 Mev. The total disintegration energy is consistent with nuclear reaction $Q$-values linking ${\mathrm{Al}}^{28}$ and ${\mathrm{Si}}^{28}$. It is shown that a discrepancy of 0.4 mMU in the ${\mathrm{Si}}^{28}$-${\mathrm{Al}}^{27}$ mass difference exists when reaction data is compared to mass spectroscopic values. A mass for ${\mathrm{Al}}^{27}$ of 26.990 140±0.000 035 is proposed, based on ${\mathrm{Si}}^{28}$, ${\mathrm{P}}^{31}$, and ${\mathrm{S}}^{32}$ as standards.

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