Beryllium Spectroscopy

The beryllium spectroscopy project is a fundamental (or pure) physics project.  Fundamental physics is concerned with understanding why nature behaves the way it does.  This is the type of physics most physicists study.  Every physics professor at Smith College has a fundamental research project.  For example, Gary Felder studies the dynamics of the early universe in the first few moments after the big bang.  Nalini Easwar is interested in the complex fluid like properties of granular materials.  Nat Fortune studies why “frustrated” systems behave the way they do.  Courtney Lannert is interested in studying collective quantum-mechanical phenomena, and Doreen Weinberger is interested in understanding nonlinear optical systems.  In atomic and nuclear physics, we want to understand how all of the components of an atom come together.  If we really understand this, we should be able to model and predict what an atom will do in any environment.

This project involves performing high precision spectroscopy on the neutral beryllium isotope chain to delineate various theoretical models, test quantum electrodynamics, and help determine the nuclear charge radius of beryllium – all of which will improve our understanding of atomic theory.  Basically we shine a well calibrated laser at a beam of atomic beryllium and scan the wavelength of the laser while monitor the interaction between the atoms and the laser light.  When we see a strong atom/light interaction we know something interesting is occurring.  Specifically we know that we excited a beryllium atom into a higher energy state. Our goal is to measure, to high precision, the energy levels of various energy states.

Why do we want to do this?  Well, currently, theoretical estimates of several energy levels have more than an order of magnitude more precision than experimental measurements. Experimentally, the energy levels of beryllium are known to as many as four orders of magnitude less precision than the alkali atoms and as many as three orders of magnitude less precision than other alkali earth atoms.  Also, next year theorists are planning calculations to further improve the precision of energy levels for some states in beryllium.  As you can probably imagine, these calculations get more complicated the more protons, neutrons, and electrons your system has.  Improved experimental measurements on these states will provide critical feedback to theoretical results and improve our understanding of atomic theory by 1) determining which theoretical predictions are most accurate, 2) providing a test of quantum electrodynamics, and 3) help determine some properties of the beryllium nucleus.

Here are some fairly technical notes on what we plan to do (see picture below for a simplified energy diagram of beryllium):

  • Improve the experimental precision on the clock transition by a factor of 500 as a precursor to possible future optical lattice beryllium atomic clocks.
  • Perform high precision spectroscopy on the intercombination lines and improve the precision of the energy levels by a factor of 500, 100, and 500 respectively to assist theorists in determining and optimizing which theoretical models describe multi-electron systems to high (sub-nano-Hartree) precision.
  • Improve the transition frequency by a factor of 90 and measure the hyperfine structure to resolve theoretical conflicts between predicted hyperfine structures for the triplet S states of the 9Be atom.
  • Improve the experimental precision on the energy level by a factor of 1800 as a test of quantum electrodynamics.
  • Make high precision measurements of the and transition frequencies in order to perform Rydberg spectroscopy on the and states to determine the quantum defects and improve the precision of the ionization potential by a factor of 300. This measurement will serve as a test of quantum electrodynamics
  • Repeat many of the above measurements using the radioactive isotopes 10Be and 7Be, gaining additional information about the isotope shifts.
  • Determine the still unmeasured nuclear electric quadrupole moment for 7Be, which gives us information about the charge distribution inside the nucleus.

Figure 1:  A simplified energy level diagram of the beryllium atom.  It shows all of the laser wavelengths this project needs.

Level Current Energy
Current Error (cm-1) Error Goal
Factor Improvement
2s2p 3P0 21978.28 0.05 <0.0001 >500
2s2p 3P1 21978.92 0.01 <0.0001 >100
2s2p 3P2 21981.27 0.05 <0.0001 >500
2s2p 1P1 42565.4501 0.0013 Completed
2s3p 3S1 52080.94 0.09 0.001 ~90
2s3d 1D2 64 428.40 321 0.00055 Completed
2s4s 3S1 64506.56 0.18 0.0001 ~1800
2snp 3P >70000 ~0.1-1 0.0002
Ionization Threshold 75192.64 0.06 0.0002 ~300

Table 1: This table shows the energy levels that will be measured in this project, the current experimental values and errors for beryllium-9, and the error goals for this project.

Funding through the National Science Foundation:
PHY-1428112 (MRI)
PHY-1555232 (Early CAREER Award)