Direct Q-Value Determination of the β− Decay of 187Re

The cyclotron frequency ratio of 187Os29+ to 187Re29+ ions was measured with the Penning-trap mass spectrometer PENTATRAP. The achieved result of R=1.000 000 013 882(5) is to date the most precise such measurement performed on ions. Furthermore, the total binding-energy difference of the 29 missing electrons in Re and Os was calculated by relativistic multiconfiguration methods, yielding the value of ΔE=53.5(10) eV. Finally, using the achieved results, the mass difference between neutral 187Re and 187Os, i.e., the Q value of the β-− decay of 187Re, is determined to be 2470.9(13) eV.