gamma emission from the 31-yr isomer of Hf-178 induced by x-ray irradiation - art. no. 054305

A sample containing 6.3x10(14) nuclei of the 16(+) isomer of Hf-178 having a half life of 31 years and excitation energy of 2.446 MeV was irradiated w ith x-ray pulses derived from a device operated at 15 mA to produce bremsst rahlung radiation with an end point energy set to be 63 keV. Gamma spectra of the isomeric target were taken with two independent Ge detectors. Intens ities of the 213.4 keV (4(+)-->2(+)) and 325.5 keV (6(+)-->4(+)) transition s in the ground state band of Hf-178 were found to increase when irradiated . The largest enhancement was 1.6+/-0.3% measured in the 213.4 keV transiti on. Such an accelerated decay of the Hf-178 isomer is consistent with an in tegrated cross section exceeding 2.2x10(-22) cm(2) keV if the resonant abso rption takes place below 20 keV as indicated by the use of selective absorp tion filters in the irradiating beam.