Faculty Research Prize: High Precision Spectroscopy in Light Atoms for Tests of QED and the Development of Nuclear Structure Theory

Over the past few decades, the lightest atoms — hydrogen, helium, and lithium — provided an excellent testing ground for quantum electrodynamics (QED). With advances in theoretical methods, which have become increasingly sophisticated and robust, slightly heavier atoms have gained significant interest. At Smith College, our research focuses on measuring absolute transition frequencies and energy levels in atoms with Z = 4 to Z = 8. Specifically, we aim to determine the absolute energy of various states in the stable isotopes of beryllium, boron, nitrogen, and oxygen for current and near-term tests of QED.

In addition, spectroscopic measurements across the oxygen isotope chain provide valuable insights into nuclear structure. Oxygen isotopes all possess a closed proton shell, and traditional nuclear models predict closed neutron shells at N = 8 (¹⁶O) and N = 20 (²⁸O). However, recent evidence suggests additional closed neutron shells at N = 6, 14, and 16, challenging the conventional understanding of the shell model in neutron-rich nuclei. Another unexpected finding is that the neutron drip line for oxygen occurs at ²⁰O, well before the predicted ²⁸O. Interestingly, when a proton is added to oxygen, forming fluorine (Z = 9), up to six additional neutrons can be bound, moving the neutron drip line back to where it is predicted for fluorine, which highlights the significant role of proton-neutron interactions in nuclear stability.

In this talk, I will provide an overview of our completed measurements, current research efforts, and future plans for both QED tests and isotopic studies of oxygen in support of the development of nuclear structure theory.