Gamow-Teller beta decay and isospin impurity in nuclei near the proton drip line

It is shown that ‘‘superallowed’’ Gamow-Teller (GT) beta decays are possible for N=Z nuclei heavier than ${}_{28}{}^{56}{}_{}{}^{}\mathrm{Ni}_{28}^{}{}_{}{}^{}$, performing Hartree-Fock plus random phase approximation (Tamm-Dancoff approximation) calculations. Since Fermi-type beta decays are forbidden in N=Z even-even nuclei, it is pointed out that the main decay mode of the nuclei such as ${}_{50}{}^{100}{}_{}{}^{}\mathrm{Sn}_{50}^{}{}_{}{}^{}$ may be ‘‘superallowed’’ GT beta decay, which is a beta decay to the GT giant resonance state. The amplitude of isospin T=1 admixed to the T=0 ground state in N=Z nuclei is also calculated and discussed.