EFFECTIVE 2-BODY FORCE INFERRED FROM (P,N) REACTION ON 170 180 27AL AND OTHER LIGHT NUCLEI

Using the Livermore variable-energy cyclotron time-of-flight facility, the angular distribution of the neutrons from the (p,n) reaction on O17, O18, and Al27 has been measured in 15°steps from 0°to 135°for 13 proton energies between 7 and 13.5 MeV. The persistence of a rather large O18(p,n)F18 ground-state reaction (T=1,J=1) over the entire energy region studied clearly indicates the operation of a spin-flip mechanism in the effective two-body force. The O18 and O17(p,n) isobaric cross sections (T=0,J=0) are experimentally observed to be roughly equal, while optical-model calculations (including the isospin potential) predict O18 cross sections to be twice as large as those for O17. This disagreement can be qualitatively explained by the presence of a large spin-flip term in the effective two-body force. The O17(p,n1)F*17 (Ji=52+,Jf=12+) and the O18(p,n)F*18 (T=0,Ji=0+,Jf=2+) cross sections indicate a sizeable value for the quadrupole term in the multipole expansion of the effective two-body force. These data and other light-nucleus data are analyzed using the distorted-wave Born approximation to yield an estimate of the effective central two-body interaction. For an assumed Yukawa force with a range of 1.4 fm, this analysis yields V9 MeV and V6 MeV. A comparison is made between these force constants and those obtained from other sources. © 1969 The American Physical Society.