A process for transferring energy from electron shells into nuclear excitation, NEET, has offered the promise for modulating nuclear properties at accessible levels of power. It had been proven recently by exciting a nuclear level of 197Au with synchrotron radiation, but measured couplings were far below theoretical objectives. Reported here is an extension of that approach for excitation to 178Hf m2 isomeric nuclei. Isomeric targets were irradiated with X-rays in the beamline BL01B1 at the synchrotron radiation source SPring-8. Energies were tuned from 9 to 13 keV. In this range an excitation branch attributed to NEET was found to have a probability of 2 × 10−3 relative to L-shell photoionization. The resulting emission of exoergic γ-photons was observed from the target at a rate approaching the theoretical maximum.

A sample containing 6.3ϫ10 14 nuclei of the 16 ϩ isomer of 178 Hf having a half life of 31 years and excitation energy of 2.446 MeV was irradiated with x-ray pulses derived from a device operated at 15 mA to produce bremsstrahlung radiation with an end point energy set to be 63 keV. Gamma spectra of the isomeric target were taken with two independent Ge detectors. Intensities of the 213.4 keV (4 ϩ →2 ϩ ) and 325.5 keV (6 ϩ →4 ϩ ) transitions in the ground state band of 178 Hf were found to increase when irradiated. The largest enhancement was 1.6Ϯ0.3% measured in the 213.4 keV transition. Such an accelerated decay of the 178 Hf isomer is consistent with an integrated cross section exceeding 2.2ϫ10 Ϫ22 cm 2 keV if the resonant absorption takes place below 20 keV as indicated by the use of selective absorption filters in the irradiating beam.

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