Measuring B(E2) values in light radioactive nuclei to guide ab initio calculations
University of Notre Dame
Measuring electromagnetic transition strengths can provide stringent tests of nuclear ab initio calculations in low mass nuclei (A<20). In this mass region, there are a limited number of electromagnetic transition strength measurements available, especially for unstable nuclei. An experiment was performed with a 7Be beam at the University of Notre Dame Nuclear Science Laboratory to measure the E2 transition strength of the first excited state of 7Be. The 7Be was produced and separated with TwinSol and the γ-ray yields were measured in coincidence with scattered 7Be. This measurement of the 7Be B(E2; 3/2 -→1/2 - ), along with a previous measurement of the 7Li B(E2; 3/2 -→1/2 - ), has been used to benchmark a variety of ab initio calculations. These tests were continued by extending into the A=8 region and a similar Coulomb excitation experiment was performed to measure the B(E2; 2 +→1 + ) of the first excited state of 8Li. These two experiments, as well as the comparison of their results to ab initio calculations, will be presented. For the A=7 isobars, ab initio calculations with a variety of nuclear interactions used were all seen to agree with the experiment result, bolstering confidence in the reliability of these calculations. However, the ab initio calculations largely do not agree with the experimental measurement of 8Li and much greater variation between the calculated values is seen. While the reason for this discrepancy in these comparisons can tentatively be explained within the ab initio framework, this 8Li transition strength still presents a new challenge for these ab initio calculations to meet.
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