The proton capture cross sections of the stable molybdenum isotopes 92, 94, 95, and 98 have been measured by means of the activation method in the proton energy range between 1.5 and 3 MeV. Thin layers of natural molybdenum were irradiated at the Karlsruhe 3.75 MV Van de Graaff accelerator with proton beams of 20–55 $\mu$A. The activity induced by ($p,\gamma )$ reactions was measured with a calibrated HPGe detector. In this way, six cross sections for populating ground states and isomers in four different Tc isotopes could be determined simultaneously. The systematic uncertainties of this method are typically 4%. The fact that the resulting cross sections are 2–4 times larger than recent statistical model predictions illustrates the need of experimental data for the yet unexplored field of $(p$,$\gamma )$ reactions in the mass region beyond $A=90\mathrm{}$. The present results are important for a quantitative discussion of the production of the abundant $p$ nuclei ${}^{92}$Mo, ${}^{94}$Mo, ${}^{96}$Ru, and ${}^{98}$Ru during SN Ia explosions. They represent also a first step in establishing parameter systematics that allow for more reliable model extrapolations into the region of unstable nuclei of relevance for the $p$ process in SN II.

• Received 14 February 1997

DOI:https://doi.org/10.1103/PhysRevC.55.3127