MRI: Development of the SABRE Silicon Array for Branching Ratio Experiments

Two of the most compelling questions in science are: how were the elements created and how are they continuing to be synthesized today. Understanding the origins of the elements explains the origins of Earth. Exotic nuclei are often created in the astrophysical cauldrons of explosive alchemy, and the probabilities that these newly synthesized nuclei can retain the charged particles that created them determines whether heavier nuclei can be formed in the process.

The origin of the elements is ultimately tied to this competition between particle emission and absorption. This MRI development award will provide funds to build SABRE (Silicon Array for Branching Ratio Experiments) that will be combined with the unique TriSol facility at the Notre Dame Nuclear Science Lab (NSL) – and that new instrumentation will be used to measure particle-emission probabilities for nuclei critical to explosive nucleosynthesis.

Proton and alpha-induced reactions on exotic nuclei dominate the heavy-element nucleosynthesis in explosive environments such as novae, supernovae, and X-ray bursts. The new SABRE array in the TriSol facility at NSL will allow scientists to measure proton and α branching ratios as small as 10e−5. The key feature of this spectrometer is that it will allow experimenters to select specific reaction products that identify individual states of the resulting nucleus in a spectrum that is essentially background free.

That capability is what will allow the group to measure such low branching ratios and have significant impacts on understanding capture reactions at stellar temperatures. A prime example is the 15O(α, γ)19Ne reaction because of its key importance in triggering heavy element nucleosynthesis via the rapid proton-capture process.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.