Evidence for the forced gamma emission from the 31-year isomer of hafnium-178

A sample containing 0.63 x 10(15) nuclei of the 4 quasiparticle isomer of H f-178 having a half life of 31 years and excitation energy of 2.45 MeV was irradiated with X-ray pulses derived from a commercial X-ray unit typically used in dental medicine, it was operated at 15 mA to produce Bremsstrahlun g radiation with an endpoint energy of 90 keV, With a high purity Ge detect or the number of gamma photons collected from transitions between the lower members of the ground state band was found to increase by about 2% above t hat emitted by spontaneous decay of the isomer, Such an enhancement is cons istent with an integrated cross section of 2 x 10(-21) cm(2) keV, a value i n agreement with results scaled from comparable measurements for Ta-180. Ho wever, this is believed to be the first observation of photon initiated gam ma emission, with a substantial gain in energy. This result has considerabl e significance to the development of a gamma-ray laser.