Constraining the astrophysical p process: Cross section measurement of the Kr 84 (p,γ) Rb 85 reaction in inverse kinematics

One of the biggest questions in nuclear astrophysics is understanding where the elements come from and how they are made. This work focuses on the p process, a nucleosynthesis process that consists of a series of photodisintegration reactions responsible for producing stable isotopes on the proton-rich side of stability. These nuclei, known as the p nuclei, cannot be made through the well-known neutron-capture processes. Currently p-process models rely heavily on theory to provide the relevant reaction rates to predict the final p-nuclei abundances and more experimental data is needed. The present work reports on an experiment performed with the SuN detector at the National Superconducting Cyclotron Laboratory, NSCL, at Michigan State University using the ReA facility to measure the Kr84(p,γ)Rb85 reaction cross section in inverse kinematics. The reverse Rb85(γ,p)Kr84 reaction is a branching point in the p-process reaction network that was highlighted as an important reaction in sensitivity studies in the production of the Kr78 p nucleus. A new hydrogen gas target was designed and fabricated and a new analysis technique for background subtraction and efficiency calculations of the detector were developed. The experimental cross section is compared to standard statistical model calculations using the non-smoker and talys codes.