Spectroscopy of ⁵⁰Sc and ab initio calculations of B(M3) strengths

The GRIFFIN spectrometer at TRIUMF-ISAC has been used to study excited states and transitions in ⁵⁰Sc following the β decay of ⁵⁰Ca. Branching ratios were determined from the measured γ-ray intensities, and angular correlations of γ rays have been used to firmly assign the spins of excited states. The presence of an isomeric state that decays by an M3 transition with a B(M3) strength of 13.6(7) W.u. has been confirmed. We compare the first ab initio calculations of B(M3) strengths in light- and medium-mass nuclei from the valence-space in-medium similarity renormalization group approach, using consistently derived effective Hamiltonians and effective M3 operator. The experimental data are well reproduced for isoscalar M3 transitions when using bare g factors, but the strength of isovector M3 transitions are found to be underestimated by an order of magnitude.