Analogous Gamow-Teller and M1 transitions in 26Mg, 26Al, and 26Si -: art. no. 064312

Under the assumption that isospin T is a good quantum number, isobaric analog states and various analogous transitions among these states are expected in isobars with mass number A. Strengths of analogous Gamow-Teller (GT) and M1 transitions have been compared for an A = 26 isobar triplet with T-z = + 1, 0, and - 1, where T-z is defined by T-z = (N - Z)/2. The T-z = 1 --> 0 GT transitions from the J(pi) = 0(+) ground state of Mg-26 to excited J(pi) = 1(+) states in Al-26 were studied up to the excitation energy (E-x) of 9 MeV by using a high energy-resolution (He-3,t) reaction. The distribution of observed GT strengths was well reproduced in a shell-model calculation. The isospin symmetric T-z = -1-->0 GT transitions can be studied in the Si-26 beta decay. The GT strengths from the (He-3,t) reaction were in good agreement with the beta-decay values evaluated up to E-x = 2.7-MeV states in 26Al. The GT strengths were further compared with the strengths of analogous M1 gamma transitions in Al-26, i.e., the M1 transitions from the excited 1(+) states to the isobaric analog state of the Mg-26 ground state in Al-26. Through this comparison, contributions of spin and orbital terms in these M1 transitions were studied. The GT and M1 strengths as well as spin and orbital contributions in M1 strengths are interpreted by both the shell model and the particle-rotor model assuming a correlated proton and neutron pair around a Mg-24 core. The isospin T of each excited 1(+) state in Al-26 was also studied by examining the existence or the nonexistence of the analog 1(+) state in the T-z = 1 Mg-26 nucleus.