Experimental Investigation and R-matrix Analysis of Low-lying Levels in 5He and 5Li

Abstract

The ~cle-unstable nuclei SHe and Su have been studied via the 4He<,U,6U)SHe and 4He( Li,6He)SU stripping reactions at beam energies of 50 MeV and the 6U(12C, 13N)SHe and 6Li(13C, 14C)SU pickup reactions at 90 MeV. The experimental data clearly demonstrate a dependence of the lineshapes on the method of production of the mass-5 nuclei (in this case pickup or stripping). The observed lineshapes were analysed using the R-matrix formalism in a two-level approximation for each r value, with parameter values deduced from fits to the available 4He + nucleon scattering data. A best channel radius of 5·5 ± 1· 0 fm was determined from the stripping data, and the corresponding set of R-matrix parameters also provided a satisfactory description of the pickup data. This channel radius is significantly larger than that employed in most previous analyses. Properties of the lowest ~ - and ! - sta~s of SHe and sU, observed via direct reactions, ate deduced from the parameter values. These properties are compared with results from earlier experimental analyses and the inferred properties of positive-parity states are compared with the results of recent shell-model calculations.