Precision Measurements on Ions

Florida State University, Tallahassee FL

Investigators

Abstract

Non-technical description: The Florida State University cryogenic Penning trap mass spectrometer is currently the world's most precise apparatus for measuring atomic masses (more colloquially, for "weighing atoms"). The mass of an atom is a basic property and so atomic masses have many important applications in chemistry and physics. 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 the mass of the neutrino, an extremely light and weakly interacting fundamental particle that pervades the universe. For years it was believed that the neutrino had no mass. We now know this not to be the case, and this new knowledge raises fundamental questions concerning the origin and structure of the universe. The project also provides training for student and post-doctoral researchers who are likely to make careers in academe, industry or national laboratories, hence contributing to the scientifically trained workforce. Technical description: Three of the measurements we propose will provide atomic mass differences, or nuclear Q-values, that will be used to test systematics in other projects that seek to set upper limits on the mass of the electron anti-neutrino from low energy beta-decays. These are measurements of the 3T-3He mass difference for the ongoing, very-large-scale tritium beta-decay spectrometer KATRIN; and the mass differences 187Re-187Os and 163Ho-163Dy, for projects that will use micro-calorimeter beta-decay spectrometers. Other measurements on light ions will reduce the uncertainty of the atomic mass of the proton. Another mass difference, 35Cl-36Cl, will enable a check of precision gamma-ray metrology. Measurements of the atomic masses of 40,48Ca are also planned, to enable ongoing precision g-factor measurements of 40,48Ca19+ to test relativistic atomic theory for the g-factor of hydrogen-like ions and to probe the dependence on nuclear structure. The measurements will consist of ratios of cyclotron frequencies of pairs of ions in the 8.5 tesla magnetic field of the FSU Penning trap mass spectrometer. Unique features of this spectrometer include the ability to make and isolate, in the Penning trap, a single ion of nearly any element; phase-coherent detection of the axial motion of an ion, via image currents, using a high-Q super-conducting tuned-circuit coupled to a dc-SQUID; and measurement of the ion's cyclotron frequency by mapping evolved cyclotron phase onto axial motion using an rf pi-pulse at the cyclotron-to-axial coupling frequency. Cyclotron frequency noise due to variation in the magnetic field is reduced by trapping both ions in the pair simultaneously.