Measurements on Radionuclides for Stellar Element Production

All elements from Carbon onwards that we observe in the Universe were produced by nuclear reactions inside stars. The basic mechanisms of synthesizing the elements have been understood for several decades. Nevertheless there are many open questions, in particular concerning the specific astrophysical scenarios where element synthesis takes place, specifically involving the role of radioactive nuclides. During the Erwin Schrödinger Fellowship, I want to address key questions of nucleosynthesis in stars by working within the nuclear physics group at the University of Edinburgh, an internationally leading group in the field of nuclear astrophysics. I plan to study critical destruction reactions of the cosmic gamma ray emitter aluminum-26 (26Al) which is produced in supernova explosions. 26Al has been observed by satellite telescope missions and is proof for ongoing nucleosynthesis in stars. I plan to measure neutron induced reactions on 26Al at the neutron time-of-flight facilities n_TOF at CERN and GELINA at the Institute of Reference Materials and Measurements, Belgium. The charged particles emitted in these reactions will be detected using advanced silicon strip detectors developed at the University of Edinburgh. Edinburgh is renowned for their world-leading expertise on silicon detectors. The experience gained in these experiments can be used to study other reactions involving charged particle detection with silicon detectors at n_TOF during my return phase at Vienna. The second part of my research proposal deals with the production of heavy elements. I will collaborate on experiments studying critical nuclear properties for the rapid neutron capture process producing heavy elements, such as half lives, beta-delayed neutron emission and masses of exotic, radioactive species. The proposed experiments will take place at the radioactive beam facility RIKEN in Japan, using the Advanced Implantation Detector Array AIDA, whose construction was led by the University of Edinburgh. AIDA is planned to be combined with the beta delayed neutron detector BELEN. Additionally, I will study the production of heavy elements by measuring neutron capture cross sections on germanium isotopes at the n_TOF facility, which is critical for understanding the formation of the heavier species from Arsenic to Yttrium. The last part of my research plan concerns the production of proton rich isotopes via proton and alpha induced reactions. I plan to collaborate on experiments to study those reactions in storage rings, a novel and innovative approach with many advantages compared to traditional methods. The University of Edinburgh is developing detectors that can be operated in the ultra high vacuum of storage rings and is a leading member of the TSR@ISOLDE project which foresees the installation the test storage ring at the HIE-ISOLDE setup at CERN.

The origin of the chemical elements in our cosmos is a main open question in modern physics. All elements heavier than Carbon are produced by nuclear reactions inside stars. During the Schrödinger Fellowship at the University of Edinburgh, UK, I investigated several unsolved problems regarding the synthesis of elements. I measured nuclear reactions as they happen in a star in the laboratory to explain elemental abundances in our cosmos and the astrophysical environments where nucleosynthesis takes place. This included measurement of the destruction of aluminium-26 by neutrons. The radioactive aluminium-26 was discovered to be present in our galaxy by satellite missions, which is proof that nucleosynthesis is still ongoing in our galaxy. To detect reactions of neutrons with aluminium my colleagues at Edinburgh and myself developed a Silicon Strip detection system. The measurement of neutron induced reactions on aluminium-26 was successfully performed at the Institute for Reference Materials and Measurements (IRMM) in Belgium. Results of this measurements will help to better understand the supernova mechanism, which is responsible for producing aluminium-26, and the abundances of aluminium-26 in our galaxy. The astrophysical environments responsible for production of elements heaver than iron are still unknown. Neutron capture measurement on germanium isotopes were conducted at the neutron time of flight facility n_TOF at CERN. The measurement of neutron capture probabilities is important to explain abundances of the elements from germanium to yttrium, but also to investigate and understand the abundances of elements in very old, ultra metal poor stars. The last part of the Fellowship related to the production of proton rich isotopes by proton and alpha particle induced reactions. The Schrödinger Fellowship allowed to collaborate on innovative experiments measuring nuclear reactions using storage ring, a new method which promises several advantages compared to traditional methods. First experiments were conducted at the experimental storage ring ESR at the GSI laboratory in Darmstadt. Summarizing, the Schrödinger Fellowship offered the unique possibility to work at an internationally renowned University with leading scientist in the field and perform experiments addressing key open questions in understanding the origin of the chemical elements.