Partial cross sections of the 92Mo(p,γ) reaction and the γ-strength in 93Tc

Background: For a p nucleus, 92 Mo has a high natural isotopic abundance of over 14 %. The γ-process nucleosynthesis is believed to produce 92 Mo, but fails to explain its large abundance, especially with respect to the other p nuclei produced in the same stellar environment. Further studies require precise nuclear models for the calculation of reaction cross sections. Purpose: A measurement of the total and partial cross sections of the 92Mo(p,γ)93Tc reaction allows a stringent test of statistical model predictions. Not only different proton+nucleus optical model potentials, but also the γ-ray strength function of 93Tc can be investigated. In addition, high resolution in-beam γ-ray spectroscopy enables determination of new precise nuclear structure data on 93Tc.
Method: Total and partial cross-section values were measured by means of the in-beam method. Prompt γ-rays produced during the irradiation of 92Mo with protons at seven different energies between 3.7 MeV to 5.3 MeV were detected using the high-purity germanium (HPGe) detector array HORUS at the Institute for nuclear Physics, University of Cologne. The γγ-coincidence method was applied to correlate γ-ray cascades in 93Tc with their origin in the 92Mo+p compound state.
Results: The measured cross sections are compared to Hauser-Feshbach calculations using the statistical model code TALYS on the basis of different nuclear physics input models. Using default settings based on standard phenomenological models, the experimental values cannot be reproduced. A shell model calculation was carried out to predict the M1 strength in 93Tc. Together with Gogny- or Skyrme-HFB plus Quasi-Particle Random Phase Approximation (QRPA) for the gamma-ray strength model, the description between experimental data and theoretical predictions could be significantly improved. In addition, deviations from the adopted level scheme were found.
Conclusions: Using Gogny- or Skyrme-HFB+QRPA E1 and shell-model M1 strength, statistical model predictions can be significantly improved. Partial cross sections provide a valuable testing ground for γ-ray strength functions for nuclear astrophysics applications. In addition, they can be used to investigate nuclear-structure properties of the compound nucleus.