Invariant Mass Spectroscopy for the Neutron Rich Nuclei

The neutron-rich carbon isotopes (19,17)C and a boron isotope (14)B are investigated respectively via proton inelastic and charge-exchange reactions on a liquid hydrogen target at around 70 MeV/nucleon at RIKEN. The invariant mass method in inverse kinematics involving coincidence detection of a charged fragment and a neutron both emitted at forward angles is employed to map the energy spectrum above the neutron decay threshold. Several resonance structures are revealed in the invariant mass spectra, and the nature for some of them is discussed from comparisons of differential cross section data with predictions of microscopic DWBA calculations based on spsdp f shell model wave functions and a recent parametrization of semi-microscopic nucleon-nucleus optical model potential (JLMB). By extrapolating the (p, n) cross sections leading to the 1(+) state at 1.27 MeV in (14)B to zero momentum transfer the Gamow-Teller transition strength is deduced. The value is found to compare well with that reported in a beta-delayed neutron emission study.