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

The cyclotron frequency ratio of ^187OOs²⁹⁺ 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.