WHAT IS NEW IN ATOMIC MASS DETERMINATIONS?

              Aaldert H. Wapstra and Georges Audi

    Atomic mass determinations with Penning traps have considerably
    improved the precision in our knowledge of the masses of
    fundamentally important atoms like the three lightest hydrogens and
    the two lightest heliums. A new determination of the capture gamma
    ray leading to deuterium then also leads to an improved mass value
    for the neutron. And the recent evaluation of natural constants now
    allows to express the corresponding mass excess values, both in mass
    units and in electronvolts, essentially without loss of precision.
    This is even true for some heavier nuclides (e. g. 23Na, 86Rb??,
    133Cs) for which Penning trap measurements also have yielded very
    precise mass values.

    Unfortunately, though, measurements intended to solve the 20 years
    old 20 keV uncertainty (compared to a suggested precision of less
    than 2 keV) in the masses of the mercury isotopes did not yet yield
    a convincing answer.

    Using the new data, we checked and, where necessary, improved all
    reported reaction energies for (n,gamma), (p,gamma) and (p,n)
    reactions. In some cases, this lead to removal of earlier
    discrepancies - but also new ones appeared, requiring further study.

    Continuation of the Mainz Penning trap work yielded about 10 keV
    precise mass values for many proton-rich nuclides of Xe isotopes and
    ones around 146Gd. In addition, Darmstadt measurements of frequency
    spectra in the big storage ring have yielded many, partly only
    slightly less precise values for proton-rich nuclides in the region
    A=100-200. Combination with measurements of decay energies in
    (series of successive) alpha decays (several made in Jyvaskula),
    this led to many more mass values. Thus, interesting information has
    been obtained on the course of the poton separation energies around
    and just above the proton drip line. Even more information on that
    subject arose from the continued measurements of nuclides decaying
    both by proton and alpha particle emission. Such measurements also
    yielded much information on the occurenece of isomers.

    We also looked at the resulting new information on the neutron
    pairing energies in proton-rich Hg and Pb nuclei. The
    Jensen-Hansen-Jonson estimate is decidedly better than the earlier
    formula (12 MeV)/$A sup half$.

    Several Mainz and Darmstadt measurements only yielded an average
    value for the mass of isomeric pairs, or even triplets, with
    half-lives comparable with the measuring times, nowadays one or a
    few seconds but may be less in the future. For this reason, among
    others, we partook in constructing a file NUBASE with data on
    isomers with a half-life above one milliescond. We consider to keep
    it yup to date, to lower the limit to 100 ns, and to keep it
    available om internet.

    Extremely interesting are the newly reported results on very heavy
    nuclides, up to Z=118. Though there are doubts about the validity of
    some of those reports, we intend to accept them provisionally for
    our atomic mass calculations as long as not proven wrong.

    We continue our habit to estimate mass values for nuclides for which
    no sufficient data are avauilable. For proton-rich nuclides in the
    region A<100, we make use of estimates from the isobaric multuiplet
    mass eqaution when possible; for A>230 systematics of relative
    energies of Nilsson levels.