Radiative M1 capture in light nuclei

The importance of semi-direct processes in E1 and E2 capture reactions has been well documented. Little is known, however, about M1 capture although a vast body of data indicates a non-statistical nature. We discuss here the importance of the semi-direct M1 process and concentrate in particular on recent experimental results claiming that the M1 strength in 29Si is nearly one order of magnitude smaller than in 28Si, the target nucleus. We use shell model arguments to demonstrate that this reduction is indeed consistent with the semi-direct reaction process and that other mechanisms like 2p-2h fragmentation and phonon coupling are not likely to be instrumental in elucidating further the non-statistical nature of the 28Si+n reaction. (orig.)