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B(E2) measurements in light radioactive nuclei for guiding ​ab initio ​calculations

Presented By:  Samuel Henderson /

Samuel Henderson is a graduate student working with Dr. Tan Ahn at the Notre Dame Nuclear Science Laboratory. His graduate work focuses on measuring electromagnetic transitions in light, radioactive nuclei using particle and gamma detectors. His PhD research has been based on measurements of B(E2) values in 8Li and 7Be. He has also worked extensively with theorists to compare these measurements to ab initio calculations to learn more about the structure of these nuclei. The eventual goal of this research is to forward the understanding of unusual structures in light nuclei, such as cluster structures and halo nuclei, and provide experimental benchmarks for ab initio calculations. After completion of his degree, Samuel intends to continue research in nuclear structure and also pursue research in support of nuclear energy applications.


Ab initio​ calculations are capable of describing nuclear properties in low mass nuclei from the basic building blocks of nucleons and their interactions. Different nuclear interactions and techniques are used in the ​ab initio​ framework to calculate experimental observables, which when verified by experiment, can guide these calculations. Measuring electromagnetic transition strengths can provide stringent tests of these ​ab initio​ calculations, but many are limited to low mass nuclei (A<20). In this region, the number of electromagnetic transition strength measurements for unstable nuclei is severely lacking. In order to provide more tests of ​ab initio calculations, Coulomb excitation experiments were performed to measure the E2 transition strengths of the first excited state transition in ​7​Be and ​8​Li. The ​7​Be and ​8​Li were produced and separated with TwinSol at the Notre Dame Nuclear Science Laboratory and the excitation cross sections were measured using γ-ray yields produced via Coulomb excitation in coincidence with the scattered nuclei. The B(E2; 3/2​-​ → 1/2​-​) of ​7​Be and the B(E2; 2​+​ → 1​+​) of ​8​Li were deduced from these experiments, then compared to No-Core Shell-Model and Green’s Function Monte Carlo calculations with several different interactions. In the comparison to the ​ab initio calculations, it was found that taking a ratio of the transition strengths in ​7​Be and its mirror nucleus, ​7​Li, yielded a robust and converged value across all the considered ​ab initio calculations. Further, the ​ab initio​ calculations for this ratio showed no dependence on the choice of interaction and were in good agreement with each other and the experimental results. In a similar way, a ratio was constructed for ​8​Li by taking a ratio of the B(E2) with the square of the electric quadrupole moment of the ​8​Li ground state. However, the ​ab initio​ results for this ratio did vary with the interaction choice, not displaying the same interaction independence seen in the ​7​Be case, and only one interaction was in good agreement with the experimental result. This discrepancy between the two comparisons indicates a substantial difference in the structure of the first excited state in ​7​Be compared to ​8​Li. Additionally, the sensitivity of the calculated ​8​Li transition strength to the choice of interaction makes it useful for gaining insight into the interactions used by ​ab initio ​ calculations. Download AbstractPresentation Slides
Mar 4, 2021
1:00 pm (CST)
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