Facility for Rare Isotope Beams

What do atomic nuclei look like? There are several known images of nuclei: liquid droplets, independent nucleons "moving" in a mean potential, and clusters of nucleons floating in the nucleus. One of the methods to capture the different images of nuclei is the knockout reaction. In this reaction, the components of the nucleus are knocked out by incident particles at intermediate energies. If the rest of the nucleus is not disturbed except for the knocked-out particle, it can be determined to what extent the knocked-out particle was present in the nucleus and how it moved. By knocking out nucleons or clusters, the image of the nucleus captured by the independent particle or cluster image emerges. In this talk I will give an overview of our recent activities on nucleon and cluster knockout reactions from stable and unstable nuclei. From a theoretical point of view, the focus will be on the development of a new reaction model, CDCCIA, for the knockout of fragile particles.

Fingerprints of the properties of exotic nuclei on nucleosynthesis observables have been used for decades to frame our picture of how the heaviest elements in our Solar System came to be. The abundance of elements in our Sun, as well as nearby metal-poor stars, hints at multiple neutron capture nucleosynthesis processes, the slow (s), intermediate (i) and rapid (r) neutron capture processes. While the s-process terminates its heavy element production at Pb-208, we know that the r-process or i-process must be capable of going beyond since we observe long-lived actinides like U-238 in stars and traces of Cm-247 in meteorites. However, which astrophysical site(s) are responsible for actinide production, and exactly how heavy each nucleosynthesis process can ultimately reach remains unclear. Utilizing metal-poor stars rich in r-process elements, we will explore recent work that has suggested signatures of fission fragments of isotopes with A~260 to be observed. I will also discuss a recent application of machine learning to decipher metal-poor star abundance patterns. Further, we will discuss the utility of MeV gamma-rays, in particular a 2.6 MeV emission line of Tl-208 that could be used to hunt locally for in situ neutron capture nucleosynthesis from both i-process and r-process sources. I will also discuss the opportunity to refine our understanding through measurements at radioactive isotope beam facilities in the near future, such as constraints on neutron captures along the Tl isotopic chain. It is via studies such as these, which work to combine the current picture of leading astrophysical candidates with carefully considered nuclear data, that the big picture of heavy element origins can be teased out.

TBD

Gravitational waves are tiny ripples in the fabric of spacetime that travel to us from some of the most extreme events in our Universe, distant mergers of black holes and neutron stars. Observations of these events chart the history of stars through the collapsed remnants that are left behind at the end of their lives. Interpreting the patterns of their waves tells us about how these compact remnants orbit and spin, and can tell us how matter behaves at densities beyond that of an atomic nucleus. Mergers involving neutron stars are engines of transient astronomy, launching gamma-ray bursts and spreading newly created heavy elements into the universe. In this talk, I will tell some of the story of this new field of gravitational wave astronomy and show how our first detections are laying the groundwork for future observatories that can see across our entire Universe. Jocelyn Read is a Professor of Physics at California State University Fullerton in the Nicholas and Lee Begovich Center for Gravitational Wave Physics and Astronomy, and currently a Visiting Fellow at the Perimeter Institute. Her research connects the nuclear astrophysics of neutron stars with gravitational wave observations. She earned her Ph.D. in 2008 from the University of Wisconsin Milwaukee, where she developed a widely used model for dense matter inside neutron stars and produced first estimates of how gravitational waves from neutron star mergers would inform these properties. Her work has included proposed mechanisms for precursor flares in gamma-ray bursts, new methods for gravitational-wave cosmology, uncertainty quantification for neutron-star merger source modeling, and measurements of dense matter properties with LIGO and Virgo gravitational-wave observations. She is actively contributing to the development of the next-generation gravitational-wave observatory Cosmic Explorer. Read co-chaired the LIGO/Virgo Binary Neutron Star Sources Working Group from 2014 to 2016 and was part of the team awarded the 2016 Special Breakthrough Prize in Fundamental Physics for the discovery of gravitational waves. She co-led the Extreme Matter team of the LIGO-Virgo-Kagra Collaboration from 2016 to 2022, through the first discovery and analysis of gravitational waves from a neutron-star merger. She has held visiting positions at the California Institute of Technology and the Carnegie Observatories in Pasadena. Read chairs the Advisory Board for the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) and served on the Scientific Advisory Committee for the Australian Research Council Centre of Excellence for Gravitational Wave Discovery (OzGrav). She was elected a Fellow of the American Physical Society (APS) in 2019.

Nuclear reactions among charged particles in stars take place at energies generally well below the Coulomb barrier, so the Coulomb barrier penetration factor exponentially suppresses the cross sections down to values as small as few nanobarns or picobarns. Therefore, approaching astrophysical energies opens new challenges and calls for new approaches. I will introduce the mission of nuclear astrophysics and discuss how experiments are usually conducted. Then, I will focus on the use of indirect methods as complementary approaches to direct measurements, discussing in detail the asymptotic normalization coefficient (ANC) and the Trojan Horse Method (THM). These methods are used to deduce the astrophysical factors of reactions with photons and charged particles in the exit channel, respectively, with no need of extrapolation. I will present recent results of the application of the two methods as examples. First, I will discuss the 6Li(3He,d)7Be measurement used to deduced the ANC’s of the 3He+4He->7Be and p+6Li->7Be channels and the corresponding radiative capture astrophysical factors. Then, I will illustrate the THM measurement of the 27Al(p,a)24Mg astrophysical factor through the 2H(27Al,a24Mg)n reaction. The reaction rate of the 27Al(p,g)28Si reaction was also deduced thanks to the determination of the proton partial widths. Both the ANC and the THM applications made it possible to assess the occurrence or exclude the presence of resonances that could be responsible significant changes of the reaction rates at temperatures of astrophysical interest.