  For the first time a direct determination of the atomic mass difference of
187Re and 187Os has been performed with the Penning-trap mass spectrometer
SHIPTRAP applying the novel phase-imaging ion-cyclotron-resonance technique.
The obtained value of 2492(30stat)(15sys) eV is in excellent agreement with the
Q values determined indirectly with microcalorimetry and thus resolves a
long-standing discrepancy with older proportional counter measurements. This is
essential for the determination of the neutrino mass from the beta-decay of
187Re as planned in future microcalorimetric measurements. In addition, an
accurate mass difference of 187Re and 187Os is also important for the
assessment of 187Re for cosmochronology.
