Excitation of analogue isovector resonances via the (n,p) reaction at 60 MeV

Publisher Website
Google Scholar
Abstract
The (n,p) charge-exchange reaction is used as a selective tool for studying T+1 isovector excitations. Here, 60 MeV neutrons have been used to measure (n,p) spectra from a range of nuclei. For 6Li and 7Li large components of l=1 dipole strength, not seen in photoneutron data, have been found at higher excitation. In the cases of 6Li, 12C and 16O comparison with photonuclear and (d,2He) data indicates that most of the l=1 strength appears to be s=0. Gamow-Teller (GT)-type transitions have been measured in 6Li, 12C and 28Si and a measure of nu sigma tau , the isovector spin-dependent component of the effective nucleon-nucleon interaction, has been obtained at 60 MeV. In the Ni isotopes, increasing blocking of the GDR with N-Z is seen. A structure of substantial strength in 209Bi(n,p)209Pb, originally thought to be isovector quadrupole, may more probably be evidence of a 2h(cross) omega sigma tau -type excitation.