Beta-delayed proton and gamma emission in the decay of $$^{21}$$
21
Mg has been measured at ISOLDE, CERN with the ISOLDE Decay Station (IDS) set-up. The existing decay scheme is updated, in particular what concerns proton transitions to excited states in $$^{20}$$
20
Ne. Signatures of interference in several parts of the spectrum are used to settle spin and parity assignments to highly excited states in $$^{21}$$
21
Na. The previously reported $$\beta $$
β
p$$\alpha $$
α
branch is confirmed. A half-life of 120.5(4) ms is extracted for $$^{21}$$
21
Mg. The revised decay scheme is employed to test mirror symmetry in the decay and to extract the beta strength distribution of $$^{21}$$
21
Mg that is compared with theory.