Investigation of Compound Nucleus Reactions on the Target Nuclei 88Sr and 89Y with Polarized Protons

Abstract

In scattering experiments, where the energy resolution is much greater than widths and spacings of the finestructure resonances, the energy averaged cross section is a sum of the direct (DI) and compound nucleus (CN) cross section. The polarization dependent part of the cross section 〈σA〉, which is independent of the CN-scattering, can be used to determine the direct part of the cross section and from that σCN = 6exp − σDI 1). We have investigated the proton induced CN-reactions on the target nuclei 88Sr and 89Y near the lowest isobaric analog resonances (IAR). In this energy region around 5 MeV direct inelastic reactions are strongly reduced due to the Coulomb barrier and the (p,n)-reactions proceed to 3 levels in the residual nuclei 88Y and 89Zr, respectively. Most partial waves have weak or medium absorption, the absorption is strong for the resonant d5/2 partial wave at resonance energy and for the neutron p-waves. The simultaneous description of compound-elastic and (p,n)-cross sections allows a critical test of the various Hauser-Feshbach formulas2, 3) for a situation, where only few channels are open and furthermore weak and strong absorption is present. Recently a similar test of CN-formulas has been made by Genz et al.4) in a many channel case (Ep ≈ 6.1MeV near the S1/2 IAR observed in the (p,po) and (p,n) reactions on88Sr), where the compoundelastic cross section has been extracted from a fluctuation analysis.