We have observed the excitation of the 29.83 keV nuclear level of the radioactive ${}^{40}\mathrm{K}$ nuclide, which level is not populated by any radioactive source, by synchrotron radiation for the first time. The absolute energy of the level of $29.834\pm 0.011\mathrm{keV}$ and the half-life of $4.13\pm 0.12\mathrm{ns}$ were obtained from our measurements. Our success in observing the nuclear excitation of radioactive ${}^{40}\mathrm{K}$ in a KCl powder sample shows the possibility for study of the local vibrational states and the electronic states of potassium in various areas of research.

• Received 26 August 1999

DOI:https://doi.org/10.1103/PhysRevLett.84.566