Eur. Phys. J. A (2004) 19: 25-31
https://doi.org/10.1140/epja/i2003-10115-2

Suppression of Gamow-Teller and M1 transitions in deformed mirror nuclei ²⁵Mg and ²⁵Al

Direct observation of K selection rules

¹ Department of Physics, Osaka University, 560-0043, Osaka, Toyonaka, Japan
² Research Center for Nuclear Physics, Osaka University, 567-0047, Osaka, Ibaraki, Japan
³ Kernfysisch Versneller Instituut, Zernikelaan 25, 9747, AA Groningen, The Netherlands
⁴ Division of Mathematical Physics, LTH, University of Lund, P.O. Box 118, S-22100 , Lund, Sweden
⁵ Department of Physics, Kyoto University, 606-8502, Kyoto, Sakyo, Japan

^* e-mail: fujita@rcnp.osaka-u.ac.jp

Abstract

The mirror nuclei ²⁵Mg and ²⁵Al are expected to have very similar structures. The Gamow-Teller (GT) transitions from the ground state of ²⁵Mg to the excited states in ²⁵Al were studied by high-resolution measurements of the ²⁵Mg() charge-exchange reaction at and at 140 MeV/nucleon. Assuming the usual selection rule for the spin-isospin-type GT transitions, the states with , and 7/2 ⁺ should be excited. However, of the more than ten states with these 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 M1 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.-1