Authors:B. Gorski, S. Karamian, Yu. Oganessian, and S. Bogomolov
A method for the determination of Hf in an Yb matrix using the reaction176Hf(, 3n)177W is described. The excitation function of this reaction was measured and the4He ion energy of 36 MeV was chosen.177W was determined by -spectrometry after chemical isolation by means of extraction chromatography with tri-n-butyl phosphate. Calibration measurements were carried out with known quantities ofnatHf. The sensitivity limit obtained was at the level of 3·10–8 g/g. The Hf admixtures innatYb and176Yb samples were estimated quantitatively.
Authors:J. Kim, D. Trubert, O. Constantinescu, S. Karamian, Yu. Oganessian, Ch. Briancon, and M. Hussonnois
Neutron activation analysis has been applied to determine the purity of super-enriched176Yb as well as a diagnostic to optimize yields from the P.A.R.I.S. mass separator at Orsay. In 25 mass separations carried out during 3 months, 910 mg of super-enriched176Yb2O3 were recovered from the original 7 g of176Yb2O3 (97.5% enrichment). Neutron activation analysis has shown that only two per thousand of the initially present174Yb remained in the super-enriched product. Using this176Yb super-enriched (99.998%) target, micro-quantities of the high spin (16+) isomer178m2Hf were produced by the (,2n) reaction at the U-200 cyclotron in Dubna. Quantities of about 2·1012 atoms of this isomer have been irradiated by thermal neutron at the ORPHEE Reactor, Saclay. Only the neutron capture giving rise to the isomeric state 25/2– of179Hf has been measured, by detection -rays of this 25.1 days isomer. A cross section of 45±5 barns was obtained for178m2Hf(n,)179m2Hf.
Authors:J. Kim, J. Morel, M. Etcheverry, N. Coursol, D. Trubert, O. Constantinescu, S. Karamian, Yu. Oganessian, Ch. Briancon, and M. Hussonnois
Nowadays large interest is attached to the production of exotic beams and targets for nuclear structure and reaction studies. The nucleus178Hf, with is long-lived (T1/2=31 years) high-spin isomeric statel=16+ at a relatively low-excitation energy (2.446 MeV), is indeed a unique probe for studying phenomena in a new way. A wide research program has been underway in the framework of the Hafnium Collaboration which now concems around 80 scientists. Various targets have been prepared and adapted to different types of experiments. Irradiation processes with high-intensity beams, high-purity chemistry methods and isotopic separations have been developed. The obtaining of appreciable amounts of very high purity178m2Hf by isotopic separation, has made it possible for us to carry out -ray measurements with good statistics and high energy resolution with a -spectrometer, in order to use this isomer as a calibration standard in the 200 to 600 ke V energy range. For example, relative to the main -rays, energies have been determined with an absolute uncertainty of about 2 e V and photon emission probabilities with a relative uncertainty better than 1%.