PRECISE MEASUREMENT OF GAMMA-RAY ENERGIES AND GAMMA-RAY EMISSION PROBABILITIES IN HF-178M2 DECAY

Nowadays large interest is attached to the production of exotic beams and targets for nuclear structure and reaction studies. The nucleus Hf -178, with its long-lived (T-1/2 = 31 years) high-spin isomeric state I-pi = 16(+) at a relatively low-excitation energy (2.446 MeV), is ind eed a unique probe for studying phenomena in a new way. A wide researc h program has been underway in the framework of the ''Hafnium Collabor ation'' which now concerns around 80 scientists. Various targets have been prepared and adapted to different types of experiments. irradiati on processes with high-intensity beams, high-purity chemistry methods and isotopic separations have been developed The obtaining of apprecia ble amounts of very high purity Hf-178m2 by isotopic separation, has m ade it possible for us to carry out gamma-ray measurements with goad s tatistics and high energy resolution with a gamma-spectrometer, in ord er to use this isomer as a calibration standard ir the 200 to 600 keV energy range. For example, relative to the main gamma-rays, energies h ave been determined with an absolute uncertainty of about 2 eV and pho ton emission probabilities with a relative uncertainty better than 1%.