Ultra-Precise Mass Measurements Using the UW-PTMS

Based on the use of a single ion, isolated at the center of a cryogenically cooled Penning trap, an environment is produced which makes this mass spectrometer remarkably free of systematic errors. The most notable developments in our quest for an ultra-high accuracy instrument were (a) the compensation of the trapping potential, (b) the discovery that motional sidebands could manipulate radial energies, (c) the use of multiply-charged ions that could improve signal-to-noise, and (d) the use of an ultra-stable superconducting magnet/cryostat system with drift <0.010 ppb/h. The dominant systematic errors are associated with radial electric fields caused by image charges in the trap electrodes and with the rf-electrical drive field used to determine the harmonic axial resonance. To illustrate the potential of this improved spectrometer, the four-fold improved measurement of the proton's mass and the eight-fold improved measurement of oxygen's atomic mass will be described. This revised version was published online in July 2006 with corrections to the Cover Date.