a Determination of the Proton/electron Mass Ratio and the Electron's Atomic Mass via Penning Trap Mass Spectroscopy.
Abstract
The University of Washington Penning trap mass spectrometer has been used to obtain a ten fold improved measurement of the electron's atomic mass. The trap alternately confines a single C^{6+} ion and either a single electron or a small cloud of 5 to 13 electrons in a 58 kG uniform magnetic field in order to directly compare their cyclotron frequencies. Comparison with the neutral carbon is attained by correcting the ion mass for the removed electrons and their binding energies; this yields for the electron's atomic mass, M_ {e} = 0.000 548 579 911 1(12) u. Combining this with the accepted value of the proton's atomic mass yields the proton/electron mass ratio m_ {p}/m_{e} = 1836.152 666 5(4 0). The 2.2 ppb uncertainty is still limited by the electron's mass. The cyclotron resonances are detected via small couplings of the magnetic states to the particle's harmonic motion along the axis of the field. These couplings cause small shifts in the frequency of the axial motion which is monitored continuously through non-destructive rf detection. Previous determinations were limited in accuracy due to a second order magnetic field gradient used for the coupling to the electron cyclotron states. For the new measurement, small anharmonic terms in the trap potential are used to detect the change in both the ion's cyclotron energy and the electron cloud's axial energy collisionally transferred from the heated cyclotron motion. Relativistic effects dominate in the description of these line shapes and provide the coupling for the single electron. Magnetic field inhomogeniety (linear or quadratic) no longer presents a limitation. Details of the spectrometer, particle loading, cooling, and detection methods are given along with detailed expressions for the frequency shifts and systematic errors associated with the residual energies in each of the normal modes and the major perturbations to the ideal trap. Systematic corrections were applied for the electrons' residual axial and cyclotron energies and for the electrostatic image charge effects on the ion. Corrections for electron cloud number, cyclotron drive power and line splitting were found unnecessary at this level of accuracy. Magnetic field stability is the major source of statistical error.
- Publication:
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Ph.D. Thesis
- Pub Date:
- January 1995
- Bibcode:
- 1995PhDT........30F
- Keywords:
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- Physics: Atomic