Dean L. Farnham

New measurement of the proton-electron mass ratio

Abstract Using a compensated quadring Penning trap operated in a high magnetic field (5.05 T) at cryogenic temperatures (4.2 K), an r.f. resonance ion storage technique allows cyclotron resonances for both electrons and protons, alternately trapped in the same magnetic well, to be compared in order to yield the proton-electron mass ratio m p / m e = 1836.152470(76). The 41 p.p.b. uncertainty primarily reflects a systematic shift which arises from the two charge types not having the same average magnetron orbit.

Ultrastable superconducting magnet system for a penning trap mass spectrometer

A custom-designed magnet/cryostat system is described which has demonstrated remarkably improved field stability over previous designs. To shield from external magnetic noise, a custom-fabricated flux-gate device remotely senses the changes in magnetic field and cancels them out at the site of the magnet/cryostat via a 1.7-m-diam Helmholtz coil. To provide further shielding, the basic superconducting solenoid includes a passive flux-stabilizing coil. To stabilize internal field shifts, the temperature of the materials in the immediate vicinity of the solenoid (which have a temperature-dependent susceptibility) is stabilized via the new cryostat geometry and by controlling the pressure of the evaporating liquid helium to a few parts per million. As a result, the total system now has a composite shielding factor of approximately 104 and an overall temporal stability on the order of 17(2) parts in 1012 per hour. This instrument, the heart of our new Penning trap mass spectrometer, has recently been used to d...

A Compensated Penning Trap Mass Spectrometer and the 3

Abstract The use of a compensated Penning trap to measure an ions mass relative to some calibration ion is described along with the leading systematic effects which must be considered. In this respect, magnet stability should no longer be a major limitation. This particular spectrometer has recently been used to determine preliminary atomic masses of both 3H and 3He and can be combined to yield a preliminary endpoint energy for the tritium decay (relative to neutral ground states) of 18 588(10) eV.

High precision Penning trap mass spectroscopy and a new measurement of the proton’s “atomic mass”

The Penning trap mass spectrometer (PTMS) at the University of Washington has been rebuilt into a new state-of-the-art magnet/cryostat system with external Helmholtz compensation coils (controlled by a nearby flux-gate sensor). This system gives a total magnetic shielding factor of ∼104 (which includes the effects of a passive internal flux-stabilizing coil supplied by the manufacturer). When the new magnet/cryostat is fitted with a system to control its boil-off pressure, the typical temporal field stability is ∼−0.017(2) ppb/h. The ultimate resolution of this improved spectrometer is expected to exceed 0.020 ppb with 100 hours of data using a single C4+ ion. The comparison of a C4+ ion with a C5+ ion suggests that the spectrometer’s accuracy may indeed match its resolution. To demonstrate the spectrometer’s improved performance over its previous version, the cyclotron frequency of a single proton is compared to the corresponding frequency of a single C4+ ion, yielding a determination of the proton’s ato...

Progress on the 3H-3He mass difference using the compensated Penning trap spectrometer

The use of the compensated Penning trap to measure an ions mass relative to some calibration ion is described along with the leading systematic effects which must be considered. In this respect, magnet stability should no longer be a major limitation. Sideband techniques are described that center ions in the trap and equilibrate the cyclotron motion. The spectrometers accuracy has been checked at the 1-ppb level by comparing the same atom with different charge states. The present application determines preliminary atomic masses of both 3H and 3He. These can be combined to yield an endpoint energy for the tritium decay (relative to neutral ground states) of 18 588(10)eV.

Variable magnetic bottle for precision geonium experiments

A novel technique has been developed which allows a quadratic magnetic field to be continuously varied (via a superconducting flux transformer) from the outside of an ultrahigh‐vacuum container placed within a superconducting solenoid. Enclosed within each of these vacuum vessels is a high‐precision (compensated) Penning trap which is used in a variety of geonium experiments at the University of Washington. By varying the dc current in an outer (normal) primary solenoid, the secondary current flowing within a shorted superconducting loop is varied accordingly. The superconducting loop need only be placed in a cylindrically symmetric position within the Penning trap in order to generate the B2 term, and with a clever choice of geometry, the zeroth‐order term can be totally eliminated. As an additional highlight, the uniform field from the main solenoid is drift stabilized to the same degree as the basic cancellation and further, an auxiliary trim coil can be used to fine trim the zeroth‐order null.

Physics accessible through ultrahigh resolution trapped ion mass spectroscopy

Abstract We describe how precision mass spectroscopy can test fundamental physics such as QED and CPT invariance. We also describe how mass spectroscopy can measure a variety of fundamental constants. This is followed by a brief description of the University of Washingtons compensated quadring Penning trap and a compilation of the current mass measurements it has taken.

Ground State Lamb Shift of Hydrogen-Like Uranium via rf Mass Spectroscopy

The advantages of multiply charged ions in Penning traps, coupled with demonstrated ICR linewidths of 0.1 ppb indicate that the rf mass spectrometer developed at the University of Washington is capable of weighing the ground state Lamb shift of hydrogen-like uranium to better than 10%. Recent experiments with the creation of fully stripped 12C6+ in a Penning trap via electron impact ionization suggest that a similar approach should work to obtain fully stripped 238U92+; however the loss in ionization cross-section which scales as Z-4 must be overcome.

Proton/electron mass ratio and the electron's "atomic mass"

The UW Penning trap mass spectrometer has been used to improve the values for the electrons atomic mass and the proton-electron mass ratio. The cyclotron frequency of small clouds of /spl les/15 electrons is compared with the cyclotron frequency of a single trapped carbon ion (C/sup 6+/) in order to determine their relative mass ratio. In these comparisons, a relatively uniform magnetic field is used in order to assure that each particle sees (on the average) the same field. During systematic studies, the trapping potential was changed by more than a factor of two for the electron. In addition, measurements were taken versus axial and cyclotron drive power as well as the size of the electron cloud. Since the detection mechanism is through the nonharmonic content of the trapping potential, this too was varied. Upon correcting for the lost electrons in carbon, the comparison directly yields M/sub e/=0.000 548 579 911 7(1 7) u. Using the accepted value for the protons atomic mass, we determine m/sub p//m/sub e/=1836.152 6636(58). These values are limited primarily by the present stability of the magnetic field. >

Mass Ratio Spectroscopy and the Proton’s Atomic Mass

The traditional compensated Penning trap has been used in the past to precisely measure mass ratios of positrons[1] and protons[2] relative to the electron. Present investigations may allow one to indirectly determine the neutron/proton mass ratio as well as the 3 H — 3 He mass difference to sub-ppb precision. The latter measurement may even have direct impact on the neutrino rest mass experiments[3]. It is also probable that variations of this trap will be used to make precision measurements of the antiproton relative to the proton[4]. Because of the present interest in such mass spectroscopy, a review of the basic method is in order with an emphasis on the use of multiply-charged ions for these measurements with an application to C 4+.