Enhanced decay of the 31-yr isomer of ${}^{178}\mathrm{Hf}$ induced by x-ray irradiation has been reported previously. Here we describe an attempt to reproduce this result with an intense “white” x-ray beam from the Advanced Photon Source. No induced decay was observed. The upper limits for the energy-integrated cross sections for such a process, over the range of energies of 20–60 keV x rays, are less than $2\times {10}^{-27\mathrm{}}{\mathrm{cm}}^2\mathrm{keV}$, below the previously reported values by more than 5 orders of magnitude; at 8 keV the limit is $5\times {10}^{-26\mathrm{}}{\mathrm{cm}}^2\mathrm{keV}$.

• Received 18 April 2001

DOI:https://doi.org/10.1103/PhysRevLett.87.072503