Neutron‐deficient nuclei withTzequals to −3/2 and −2 have been produced at the GANIL/LISE3 facility in fragmentation reactions of a 95MeV/u36Arprimary beam in a12Ctarget. For the first time, &bgr;‐delayed proton and &bgr;‐&ggr; emission has been simultaneously observed in the decay of21Mg,25Siand26P. The decay scheme of the latter is proposed and the Gamow‐Teller strength distribution in its &bgr; decay is compared to shell‐model calculations based on the USD interaction. The B(GT) values derived from the absolute measurement of the &bgr;‐branching ratios are in agreement with the quenching factor of about 60&percent; obtained for allowed Gamow‐Teller transitions in this mass region. A precise half‐life of 43.7 (6)mswas determined for26P, the &bgr;‐2pemission of which was studied. The expected contribution of spectroscopic studies of neutron‐rich nuclei is discussed with respect to the mirror asymmetry phenomenon occuring in analogous &bgr; decays. © 2003 American Institute of Physics