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

The cyclotron frequency ratio of ${^{187}\mathrm{Os}}^{29+}$ to ${^{187}\mathrm{Re}}^{29+}$ ions was measured with the Penning-trap mass spectrometer PENTATRAP. The achieved result of $R=1.000\text{ }000\text{ }013\text{ }882(5)$ 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 $\mathrm{\ensuremath{\Delta}}E=53.5(10)\text{ }\text{ }\mathrm{eV}$. Finally, using the achieved results, the mass difference between neutral $^{187}\mathrm{Re}$ and $^{187}\mathrm{Os}$, i.e., the $Q$ value of the ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of $^{187}\mathrm{Re}$, is determined to be 2470.9(13) eV.