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 σ^CN = 6^exp − σ^{DI 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 d_5/2 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 formulas^{2, 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 (E_p ≈ 6.1MeV near the S_1/2 IAR observed in the (p,p_o) and (p,n) reactions on⁸⁸Sr), where the compoundelastic cross section has been extracted from a fluctuation analysis.

Supported by the Deutsche Forschungsgemeinschaft