Beta decay of proton excess nucleus 24Si and its mirror symmetry

Characteristic properties of proton excess nuclei are investigated by the beta decay spectroscopy of 24Si by using RIKEN projectile-fragment separator (RIPS). The detailed decay scheme is decided and Gamow-Teller transition strength B(GT) is determined. Considering the mirror symmetry breaking, effects of weakly bound s-orbit protons on the nuclear structure are discussed. Comparing the asymmetry (Thomas-Ehrman shift) of the excitation energies between 24Al and 24Na, which are mirror nuclei each other, it is concluded by using the new value of the electromagnetic transition probability that the wave function configuration is not changed, although completely different result has been obtained that the configuration is changed due to the lowering of the s-orbit by using the conventional values of the transition probability. In the former case, TE shift of the related state of 24Al is interpreted by the lowering of the proton Coulomb energy due to the spatially broadened distribution that is to say on the classical picture. Considering the accuracy of the present experiment and its consistency with other experiments, the value of the electromagnetic transition probability may be further renewed. It is, however, suggested finally that the idea that change of wave function configuration caused by TE will be the key to solve the puzzling experimental results of the proton excess nuclei even though not in 24Al. (S. Funahashi)