The (3He, 7Be) reaction on light nuclei

Abstract An experimental study of the ( 3 He, 7 Be) reaction has been performed at 30 MeV with 10 B, 12 C, 16 O, 19 F, 20 Ne, 28 Si and 40 Ca target nuclei.The doublet arising from the occurrence of two bound states of the 7 Be nucleus, the 7 Be (0) 3 2 − ground state, and the 7 Be (1) 1 2 − first excited state, was resolved in all the spectra. Angular distributions up to about 90° or more in the c.m. system are presented for the strongest transitions. A mechanism of one-step pick-up of four correlated nucleons, with the internal quantum numbers of a free α-particle, in short α-pick-up, is consistent with the main characteristics of the data. Unambiguous experimental evidence, though, calls for at least a partial correction to this simplified picture: the angular distributions of 7 Be (0) and 7 Be (1) are found to be somewhat different, and the shapes of the angular distributions vary rather quickly with the incident energy. The nature and validity of the assumptions of an α-pick-up mechanism are discussed, and tentative DWBA fits to the data are obtained with a “fixed range” interaction approximation. The main spectroscopic information is that the α-transfer spectroscopic factor does not decrease between 12 C and 40 Ca. nearly as strongly as shell-model wave functions would suggest.