Study of 51Ca via three-neutron transfer

Low-lying levels in 51Ca have been studied via the reaction 48Ca(18O,15O)51Ca at a beam energy of 108 MeV. Recoiling 51Ca nuclei were detected in coincidence with 15O ejectiles, largely removing the substantial background from target contaminants that was encountered in previous work. The lowest 51Ca level identified is 1.01 ± 0.11 MeV less bound than the ground state, according to a recent measurement of the ground state mass using the 48Ca(14C,11C)51Ca reaction. Considerations of the difficulty in identifying the ground state peak suggest that published values of the mass excess should be viewed with caution, and that a definitive mass measurement is still required in order to resolve questions on the structure of the neutron rich calcium isotopes. A total of six energy levels in 51Ca have been identified and their mass excesses measured. Only two of these levels have been observed previously, via the (14C,11C) reaction. Striking differences in selectivity between the (18O,15O) and (14C,11C) transfer reactions are discussed