Test of the independence hypothesis and isospin conservation in compound-statistical reactions

Abstract

Abstract Energy spectra and angular distributions of protons and α-particles emitted in the decay of 56 Fe, 60 Ni, 63 Cu, 64 Zn, and 66 Zn were measured. These compound nuclei were produced with a given excitation energy by irradiation of appropriate targets with 14.0 MeV protons and 15–19 MeV α-particles. The proton spectra featured a low-energy peak ascribable to the (p, np) or (α, np) reaction as well as a higher energy peak due to the (p, p') or (α, p) reaction. These peaks were sufficiently well resolved that differential cross sections could be obtained for the p, np, as well as α exit channels. The α and np exit channels were found to be free of precompound effects and are not affected by isospin conservation. Comparison of these particular cross sections for both entrance channels permits a test of the independence hypothesis provided a correction is made for the different angular momentum distributions in the entrance channels. When this correction is applied on the basis of the spin-dependent statistical theory it is found that the independence hypothesis is confirmed in all cases. Comparison of the p and α exit channels leads to values of the isospin mixing fraction, μ, between the T > and T states of the compound nucleus. The values of μ are 0.4±0.2 for all five compound nuclei and correspond to Coulomb mixing widths whose value is approximately 20 keV.