Precision Measurements on Ions

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The Florida State University precision Penning trap mass spectrometer is one of the world's most precise systems for measuring atomic masses (more colloquially, for "weighing atoms"). An atom's mass is a basic property and atomic masses have many important applications in physics and chemistry. In particular, because of the equivalence of energy and mass (through "E = mc2"), atomic mass differences determine the energy released in nuclear reactions. Although many atomic masses have already been precisely measured there are several scientifically important applications where measurements at still higher precision are required. These applications include determining more precise values of the "fundamental constants," and determining the mass of the neutrino, an extremely light and weakly interacting fundamental particle that pervades the universe. The fundamental constants (for example, the masses of the electron and proton) are needed for essentially all calculations in physics. But in particular, ever-more precise values are needed so that the theories included in the so-called "Standard-Model" of particle physics can be precisely compared with experimental results. If discrepancies between the results of theory and experiment are discovered, this may lead to insights into how to modify the Standard Model, which despite great success in explaining most observations, is unable, for example, to explain the currently mysterious phenomena of Dark Matter and Dark Energy. At the same time the project provides training for student researchers, from high-school to post-doctoral, in many widely applicable scientific techniques, preparing them for careers in industry and national laboratories as well as academe, hence contributing to the scientifically trained workforce.The basic method is to measure ratios of cyclotron frequencies of single ions in a precision, cryogenic, 8.5 tesla Penning ion trap using phase-coherent techniques, with ion detection via image currents using a dc-SQUID. Measurements to be accomplished will include the mass ratio of the deuteron to the proton (relevant to ultra-precise spectroscopy of hydrogen, deuterium and their diatomic molecules), of tritium to helium-3 (relevant to neutrino mass), the atomic masses of alkali metals (for the fine structure constant), of chains of calcium isotopes (for testing quantum-electrodynamics theory), and other isotope chains (for searches for deviations from so-called King-plot linearity of isotope shifts, which may point to new physics). Aiming for a few parts-per-trillion fractional precision for some measurements, the PI plans to develop a method for the simultaneous measurement of the cyclotron frequencies of two ions in a Penning trap, in which the two ions are in a coupled magnetron orbit. (This method was initially developed at MIT c. 2000, but was only applied to four ion pairs, and not to hydrogen or helium isotopes.) By measuring the cyclotron frequencies simultaneously, the measurement will greatly suppress the effect of variation in the magnetic field, which is the main cause of statistical uncertainty in the measurements of a cyclotron frequency ratio.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.