S. A. Karamian

K-mixing in nuclear reactions

Isomer-to-ground-state ratios are measured for the group of photon- and α-induced nuclear reactions. The photonuclear reactions on high-spin isomeric targets - 178Hfm2 (16+) and 180Tam (9-) - were detected successfully. Results are analysed from the point of view of the K-selectivity manifestation for the level population. The yields comparison with the regular values confirms strong K-mixing at high excitations.

Production, chemical and isotopic separation of the178m2Hf high-spin isomer

The 178m2Hf with its long-lived (T1/2=31 y), high-spin Iπ = 16+, isomeric state, is a challenge for new and exotic nuclear physics studies. The 178m2Hf isomer has been produced in microweight quantities using the 176Yb(α,2n) nuclear reaction, by irradiation with a high-intensity beam using the U-200 cyclotron in Dubna. Radiochemistry and mass separation methods have been developed, with the aim to separate and purify the produced Hf material. Thin targets of isomeric hafnium-178 on carbon backings have been prepared and used in experiments with neutron, proton and deuteron beams.

Evidence for K mixing in 178Hf

Systematics for the appearance of K-mixing levels for the pumping or spontaneous decay of multi-quasiparticle isomers in Hf isotopes are detailed in this letter. The possible location of such a level in the nuclide 178Hf is discussed and an experiment is proposed to investigate its existence.

Weak K hindrance manifested in {alpha} decay of the {sup 178}Hf{sup m2} isomer

An experiment has been performed to detect the {alpha} emission mode in {sup 178}Hf{sup m2} isomer decay and a partial half-life of (2.5{+-}0.5)x10{sup 10}y was measured. It was concluded that {alpha} decay is strongly retarded by the centrifugal barrier arising due to the high spin of this isomeric state. Additional analysis shows, however, that the K-hindrance in this {alpha} decay is relatively weak, despite the strong manifestation of spin-hindrance.