The β-decay spectroscopy on 24 Si was carried out in order to investigate characteristic properties of proton-rich nuclei from a perspective of mirror asymmetry. We observed two β transitions to low-lying bound states in 24 Al for the first time. The B( GT ) of 24 Si were deduced to be 0.13(2) and 0.14(2), which were smaller than those of the mirror transition by 22(11)% and 10(8)%, respectively. Through the comparison with theoretical calculations taking into account the Coulomb force and the Thomas-Ehrman shift, the mirror asymmetry of B( GT ) is attributed to the lowering of the proton 1s1/2 orbital.
β
-decay spectroscopy of
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