Response to Georges Audi Re Nature paper for inclusion in AMDC
    Newsletter 1/11/06

    "A direct test of E = mc2"

    Marking the end of the World Year of Physics the result of a direct
    test of Einstein's famous equation E = mc2 was published in Nature
    (S. Rainville et al. vol. 438, 1096 (2005). The test was based on
    the comparison of the neutron binding energies of 29Si and 33S, each
    obtained by precision Penning trap mass spectrometry ("m"), and by
    precision gamma-ray wavelength measurement ("E"). The comparison,
    at the 10-7 level, can alternatively be considered as a check of
    precision gamma-ray measurement techniques, or as obtaining a value
    for the molar Planck constant Nah. The atomic mass measurements were
    carried out by David Pritchard's group at MIT in early 2003 and used
    a novel technique with two ions in a single Penning trap. In this
    method the ion pairs to be compared, in this case 28SiH+/29Si+, and
    subsequently 32SH+/33S+, were placed in a controlled, coupled
    magnetron orbit, enabling simultaneous measurement of the cyclotron
    frequencies, hence almost eliminating sensitivity to magnetic field
    variations as a source of error. This enabled mass comparison at the
    unprecedented sub 1e-11 level. More information about the technique,
    results of the high precision mass comparisons of 13CH2+/14N2+ and
    of 14N2+/12C16O+ , and of the effect of molecular polarizability on
    cyclotron frequency, are given in the previous two publications of
    the group: S. Rainville et al., Science 303, 334 (2004) and J.K.
    Thompson et al, Nature 430, 58 (2004). This work also marks the last
    of a series of major accomplishments by David Pritchard's MIT
    precision mass spectrometry group.

    "MIT mass spectrometer now at Florida State University, Tallahassee"

    In mid 2003 the MIT precision mass spectrometry group was disbanded
    and the apparatus moved to Florida State University. The FSU group
    (Edmund Myers et al.) rebuilt the system and so far has used it for
    mass measurements of 32S, 84,86Kr and 129, 132Xe using single ions
    in the Penning trap, see W. Shi et al, Phys. Rev. A72, 022510
    (2005). They have also measured the mass of 31P, using two ions in a
    trap, but alternating between large and small cyclotron orbits,
    (IJMS, in press). Work on reproducing the two-ion simultaneous
    cyclotron frequency measurement technique at FSU is in progress.