Measurement of the 85Kr(d,pg) reaction as a surrogate of the neutron capture

Neutron capture cross sections play a crucial role in the modeling of the astrophysical neutron capture processes, the s- and r-process. In the s-process, which is responsible for the synthesis of about 50% of the elements heavier than iron, measurements of (n,g) cross sections are particularly important in the so-called branching points, where the isotopes involved are radioactive and there is competition between beta-decay and neutron capture. However, directly measuring these cross sections is extremely challenging, if not impossible, due to the radioactivity of the isotopes or the difficulty in obtaining pure samples. For this reason, indirect methods have been developed to extract the (n,g) cross sections from different reactions: it is the case of the surrogate reaction method, which can calculate the (n,g) cross sections using experimental inputs from the (d,pg) reaction. 85Kr is an important branching point of the s-process, which influences both the 86Kr/82Kr ratio in presolar grains and the abundances of heavy Strontium isotopes, which are produced also by r-process. The 85Kr(n,g) cross section has never been measured directly, but 85Kr can be accelerated as a pure beam. The 85Kr(d,pg)86Kr reaction has been carried out at 10 MeV/u in inverse kinematics at Argonne National Laboratory using the HELIOS spectrometer and the Apollo array. This work presents the results of this experiment. Chapter 1 discusses the astrophysical motivation of the measurement. Chapter 2 presents the theory of nuclear structure and nuclear reactions of interest for this work. In Chapter 3, the surrogate reaction method is explained, including an example of its application. In Chapter 4, the experimental set-up is described and the data analysis process is explained, presenting the results. In Chapter 5, future measurements are presented