RUI: Measurement of the Ionization Energy of Lithium 6 and 7

The fundamental purpose of atomic physics is to understand the complex interactions and inner workings of the atom. This project will further our knowledge of the lithium atom and test one sector of our best theoretical model, known as the Standard Model of Particle Physics. Our knowledge of atomic systems is driven by both experimental and theoretical results.

This project aims to resolve a discrepancy between previous measurements of the ionization energy of lithium-7 and make a second measurement for the ionization energy of lithium-6. Ionization energy is an important parameter that can serve as a test of quantum electrodynamics (QED). Specifically, measurements of the ionization energy can be useful for confirming theoretical calculations that are used in experiments that identify and explore changes in the nuclear charge distribution for the short-lived radioisotopes of lithium.

This research takes place at a liberal arts college and will involve undergraduate students in all aspects of the work, training the next generation of scientists and engineers. In addition to work on the home campus of Assumption College, some of the work will take place at Smith College to take advantage of advanced laser equipment available there, including some enabled by a recent Major Research Instrumentation award from NSF.

This work will develop the students’ proficiencies in experimental physics which are highly transferable to a range a careers and future work. In addition, the PI will offer workshops that aim to develop physicists’ facility to engage in critical conversations in the classroom and research environments.

The PI and her students will measure the absolute transition frequencies of a large number of nS, nP, and nD states in neutral lithium-7 and lithium-6 from n = 10 to the ionization threshold to sub-MHz precision. The experiment will utilize Rydberg spectroscopy through the ionization threshold directly from the ground state, with all laser frequencies calibrated by a frequency comb.

Spectroscopy on the nP states will be performed with a single photon from the ground state between 236 nm and 230 nm. The nS and nD states will be explored through off-resonance two photon transitions between 472 nm and 460 nm, again directly from the ground state. The project will resolve experimental discrepancies in current reported values. Quantum interference effects on the 2s 2S1/2 → 2p 2P3/2 states will be explored.

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.