Potential energy surface calculations have predicted the existence of the island of triaxial strongly deformed (TSD) nuclei with N~94 and Z~72. Subsequent calculations indicated that 164,166Hf would be the most favorable even-even nuclei in the island region for finding low-lying TSD structures. But experimental discoveries of TSD bands only have been reported in 161 C163,164,165 C167Lu nuclei with the wobbling mode, a unique signature of nuclei with stable triaxiality. And experimental investigation of Hf nuclei performed with Euroball and Gammasphere produced negative results on the two Hf isotopes. Later investigations in 168Hf and 173,174,175Hf show existence of strongly-deformed bands, but none has been confirmed as TSD structures. These results motivated an extension of the search for TSD bands in the region to heavier Hf-isotopes like 171,172Hf. A Gammasphere experiment was carried out to search for triaxial strongly deformed (TSD) structures in 171,172Hf. Three strongly deformed bands in 172Hf and one in 171Hf were identified through 48Ca (128Te, xn) reactions. Linking transitions were established for the band in 171Hf and, consequently, its excitation energies and spins (up to 111/2 ) were firmly established. However, none of the 172Hf sequences was linked to known structures. Experimental evidence of triaxiality was not observed in these bands. The new bands are compared with other known strongly deformed bands in neighboring Hf isotopes. Theoretical investigations within cranked-shell models and Cranked Relativistic Mean-Field (CRMF) Calculations have been performed. Cranking calculations with the Ultimate Cranker code suggest that the band in 171Hf and two previously proposed TSD candidates in 170Hf and 175Hf are built upon proton (i13/2h9/2) configurations, associated with near-prolate shapes and deformations enhanced with respect to the normal deformed bands. Cranked relativistic meanield calculations suggest that band 2 in 175Hf has most likely a near-prolate superdeformed shape involving the high-j intruder orbitals. It is quite likely that the bands in 172Hf are similar in character to this band. In this experiment six normal deformed bands in 171Hf and five in 172Hf were identified, also known low spin structures have been extended considerably. Linking transitions to known low spin structures were well established for these five bands of 171Hf but none of 172Hf. The spin and parity determinations of these rotational bands have been performed based on DCO ratio and intensity measurement. The suggested configurations of these structures also have been proposed.
| Identifer | oai:union.ndltd.org:MSSTATE/oai:scholarsjunction.msstate.edu:td-3493 |
| Date | 03 May 2008 |
| Creators | Zhang, Yanci |
| Publisher | Scholars Junction |
| Source Sets | Mississippi State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Theses and Dissertations |
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