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²⁰Mg has been populated in the ²⁴Mg(α, ⁸He) reaction at E_α = 126.9 MeV (TR76B) and 156 MeV (RO74E) with differential cross sections (lab) of 3 ± 1 nb/sr (θ = 5°, lab) and ~ 7 nb/sr (2°), respectively. Assuming the mass of ⁸He to be 31.601 ± 0.013 MeV, the mass excess of ²⁰Mg is 17.57 ± 0.03 MeV. (WA77) adopt a mass excess of 17.568 ± 0.027 MeV, and so do we. ²⁰Mg is then stable with respect to breakup into ¹⁹Na + p [see ¹⁹Na] and ¹⁸Ne + 2p by 2.65 ± 0.03 and 2.33 ± 0.03 MeV, respectively. See (WA76L) for a display of calculations of the mass of ²⁰Mg and (72AJ02) for the earlier work. The mass excess of ²⁰Mg appears to involve a deviation from the quadratic IMME prediction (TR76B). Using the wave function predictions of (LA73) and the mass excess of ²⁰Mg (TR76B) calculate the partial τ_1/2 for the allowed Fermi transition from the 0⁺; T = 2 ground state of ²⁰Mg to the 0⁺; T = 2 state in ²⁰Na [not observed] to be ~ 3.4 sec, corresponding to a β⁺ branching of ~ 4%. See also (BE76T, SH77I).