Measurement of total and partial cross sections of the ^{90}Zr(p,gamma )^{91}Nb reaction with in-beam gamma -ray spectroscopy

Abstract

The origin of many p-nuclei remains an unsolved problem in nuclear astrophysics. While photo-dissociation reactions in the gamma -process can explain the production of many p-nuclei, some, notably ^{92,94}Mo and ^{96,98}Ru are underproduced in network calculations. The ^{90}Zr(p,gamma )^{91}Nb reaction is part of a possible (p,gamma ) reaction chain for the production of the p-nucleus ^{92}Mo. Available data show a large disagreement between the different reported cross sections measurements for the ^{90}Zr(p,gamma )^{91}Nb reaction. We measured proton capture cross sections with an enriched ^{90}Zr target using in-beam gamma -ray spectroscopy for proton energies between 2.75 MeV and 5.1 MeV. The emitted gamma -rays were detected using the HORUS (High efficiency Observatory for gamma -Ray Unique Spectroscopy) detector array at the University of Cologne, Germany. To account for the possible contribution of the ^{91}Zr(p,n) reaction, an enriched ^{91}Zr was irradiated. We measured production cross sections for the ground and isomeric state of ^{91}Nb as well as partial cross section for up to ten high-energy primary transitions. The results are in good agreement with a former in-beam gamma -ray spectroscopy measurement by Laird et al.. We provide a possible explanation for the discrepancies between our data and other available measurements.