The mirror nuclei 25Mg and 25Al are expected to have very similar structures. The Gamow-Teller (GT) transitions from the J π = 5/2+ ground state of 25Mg to the excited states in 25Al were studied by high-resolution measurements of the 25Mg(3He, t) charge-exchange reaction at 0 ° and at 140 MeV/nucleon. Assuming the usual ΔJ π = 1+ selection rule for the spin-isospin-type GT transitions, the states with Jπ = 3/2+, 5/2 +, and 7/2+ should be excited. However, of the more than ten states with these Jπ values below 6 MeV excitation energy, only the 5/2+ ground state and the 7/2+, 1.613 MeV state in 25Al were strongly populated, while all other states were strongly suppressed. The analysis of Ml transitions in 25Mg also suggested a very similar feature for the analogous M1 transitions. Both 25Mg and 25Al are known to be largely deformed, and most low-lying states can be interpreted in terms of one-particle quantum numbers in the deformed potential and the associated rotational spectra. The observed suppression can be explained in terms of the K quantum number selection rules that are inherent to axially deformed nuclei.
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