Beta and gamma decays of Jπ = 1+, 24mAl state
A β-γ spectroscopy of the Jπ, 426 keV isomeric state of 24Al (24mAl) has been carried out by using a 24Al secondary beam with high purity and high isomeric ratio. From the absolute γ-ray and β-particle intensities observed in the decay of the isomeric state, the branching ratio RB of the isomeric γ decay from 24mAl to the Jπ = 4+, ground state of 24Al have been derived. The obtained RB value of 69.6(7)% is much smaller than the previously accepted value of 82.5(30)%. The precise half-life for the isomer decay, T1/2m = 130.9(13) ms, has been also determined in this experiment. Accordingly, the M3 γ-decay strength B(M3) of the 24mAl decay becomes smaller and the total β-decay branching ratio becomes larger. In particular, the β-decay branching ratio to the ground state of 24Mg becomes 24.3(9)%, which is 2.4 times larger than the previous value of 10.1(28)%. By combining the branching ratio and the half-life, the Gamow-Teller (GT) transition strength B(GT) of 0.0194(7) is deduced for the GT transition from 24mAl to the Jπ = 0+, ground state of 24Mg. This value is in good agreement with the values derived from charge-exchange reactions.