First observation of the electron capture of ⁷⁶As

For a variety of radionuclides which decay via $\beta^{-}$ and a weak $\beta^{+}$-channel the electron-capture (EC) is not observed yet. As the interest of exact decay characteristica increased again, not least with the need of reliable data for experiments on investigation of the neutrinoless double-beta-decay, an experiment for the investigation of the $^{76}$As-EC was performed. The first time observation of the EC of $^{76}$As by this experiment resulted in a total branching-ratio for the EC / $\beta^{+}$-channel of $p_\mathrm{EC} = 0.0269 \pm \left(0.0080(\mathrm{stat.}) \pm 0.0029(\mathrm{sys.}) \right)$ and $p_\mathrm{EC} = 0.0263 \pm \left(0.0077(\mathrm{stat.}) \pm 0.0047(\mathrm{sys.}) \right)$ according to two different methods. For the branching of this decay-channel into the first excited- and the ground state of \gess a limit was obtained.