Fine structure and compound nucleus cross-section enhancement observed in the 88Sr(p, p 0) reaction near the lowest [formula omitted] isobaric analogue resonance in 89Y

Abstract

The excitation functions of the reaction 88Sr(p, p 0) at θ lab = 90°, 130° and 165° were measured at the new Dynamitron-Tandem accelerator at Bochum in the energy range 5.90 ≤ E p ≤ 6.27 MeV, i.e. near the lowest s 1 2 . isobaric analogue resonance in 89Y, in steps of 1.1 keV. These measurements were undertaken in order to demonstrate for the first time the existence of fine structure in the case where many (p, n) channels are open and where the isospin T < states overlap. The mean level width Γ < of the T < compound states and the compound elastic contribution to the cross section were evaluated by means of fluctuation averaging. By comparing the measured cross section with an optical model plus resonance calculation, the total width Γ, the partial width Γ p and the resonance mixing phase of the T > state as well as the external versus internal mixing were determined. The behaviour of the mean coherence width as a function of energy is calculated and the mean compound nucleus contribution is also estimated by analyzing the data in terms of the optical model. Various Hauser-Feshbach formulas are tested and the dependence of the elastic enhancement factor on the transmission coefficient has been studied.