Experimental constraints on the γ -ray strength function in 90 Zr using partial cross sections of the Y89(p,γ)Zr90 reaction

摘要

Partial cross sections of the Y89(p,γ)Zr90 reaction have been measured to investigate the γ -ray strength function in the neutron–magic nucleus 90 Zr. For five proton energies between Ep=3.65 MeV and Ep=4.70 MeV , partial cross sections for the population of seven discrete states in 90 Zr have been determined by means of in-beam γ -ray spectroscopy. Since these γ -ray transitions are dominantly of E 1 character, the present measurement allows an access to the low-lying dipole strength in 90 Zr. A γ -ray strength function based on the experimental data could be extracted, which is used to describe the total and partial cross sections of this reaction by Hauser–Feshbach calculations successfully. Significant differences with respect to previously measured strength functions from photoabsorption data point towards deviations from the Brink–Axel hypothesis relating the photo-excitation and de-excitation strength functions.