Cross sections and analyzing powers for the(p→,n)reaction on3Heand4Heat 200 MeV

Double-differential cross sections and analyzing powers A{sub y} for the ({rvec p},n) reactions on {sup 3}He and {sup 4}He were measured at 200 MeV between {theta}{sub lab}=0{degree} and 44{degree}. The neutron spectra from {sup 3}He({rvec p},n) are dominated by the quasifree scattering peak and show no evidence for resonances in the three-proton system. The spectra from {sup 4}He({rvec p},n) exhibit strong resonance behavior in the p{sup 3}He system at low relative p{sup 3}He energies owing to the excitation of known L=1 resonances in {sup 4}Li, but there is no distinct quasifree peak in the measured spectra. The experimental A{sub y} for {sup 3}He({rvec p},n), averaged over the experimental range of neutron energies, are similar to those for free nucleon-nucleon (NN) scattering, whereas for {sup 4}He({rvec p},n) the A{sub y} are generally larger than the free values. The cross sections at far forward angles for both {sup 3}He and {sup 4}He appear to be suppressed relative to the free {ital NN} cross sections by Pauli blocking. At most angles, the shapes of the cross section spectra from both {sup 3}He and {sup 4}He are reproduced by distorted-wave impulse approximation (DWIA) calculations using a quasifree scattering model. Specifically for {sup 4}He({rvec p},n),more » the model requires the use of an optical potential which has a strong L=1 potential resonance corresponding to the low-lying L=1 states in {sup 4}Li. {copyright} {ital 1998} {ital The American Physical Society}« less