ENHANCEMENT OF THE ISOVECTOR M1 STRENGTH IN SI-28 DUE TO MESON-EXCHANGE CURRENTS

Meson exchange currents (MEC's) can induce an enhancement of the B(M1) strength in nuclei over the corresponding Gamow-Teller strength. Such an increase was observed in Si-28 [C. Luttge et al., Phys. Rev. C 53, 127 (1996)], but the experimental ratio was much larger than shell, m odel predictions using the unified sd-shell interaction and correction s to the g factors which incorporate MEC effects. It is pointed out th at, when taking the Gamow-Teller strength from a reanalysis of the Si- 28(p,n) data as well as from a recent Si-28(He-3,t) experiment, the de rived ratio is now in good agreement with the shelf model results. Thi s finding provides strong support that the observed enhancement is due to meson exchange currents.