Nuclear reaction measurements for heavy element nucleosynthesis

Friday 27 July 2018, 12.00PM

Speaker(s): Ruchi Garg, University of Edinburgh

Part-I: 59​Cu(p,α)5​6​Ni 

Part-II: 77,78​Se,6​8​Zn(n,γ)

The heavy element nucleosynthesis is the area of research looking to predict and/or explain the observed abundances of nuclei heavier than iron. The proton rich nuclei are thought to be produced in the in hot environments such as supernovae via proton capture and the photodisintegration processes. But the observed abundances of lighter p-nuclei 9​2,94​Mo and 9​6,98​Ru are not reproduced in the stellar models using these processes. In a recent work, the 𝝼p process has been suggested as an explanation for the abundances of p-nuclei with A>64. However, in an end-point nuclear cycle involving Co, Ni, and Cu, the competition between (p,α) and (p,γ) reaction rates on the 5​9​Cu isotope could hinder the reaction flow from proceeding towards heavier elements by cycling the material back. This competition is temperature sensitive and therefore it is crucial to measure the 59​Cu(p,α)56​Ni reaction cross section in order to obtain the reliable modelling results. In addition to the reaction’s importance in understanding the origin of heavy p-nuclei, it is also of key importance for X-ray light curve, and affect the composition of burst ashes on the surface of the neutron star significantly.
Currently, there is no direct measurement of the 59​Cu(p,α)56​Ni reaction cross section. I will present the preliminary results of the first such measurement. The experiment was performed at ISOLDE facility at CERN in inverse kinematics with high intensity 59​Cu beam on CH​2​ foil target at 5 different beam energies between 3.6 - 5.0 MeV/u.

In another campaign, we are measuring the cross-sections of the neutron-capture reactions that play part in the s-process. S-process is responsible for the formation of nearly half of the abundance of heavy elements. To obtain credible results from the theoretical modelling of the process, the input of capture reaction rates is required to have less than 5% uncertainty on the stable isotopes (and sometimes on unstable isotopes that may form the branching points). I will present the method of neutron time-of-flight that is one of the few techniques that is used to make these measurements.

Location: P/T 111