Characterization of the superdeformed band in189Hg

Abstract

Abstract:Much improved data on the superdeformed band in rSgHg have been obtained in the study of the la~ 5n) reaction at 165 MeV. Energies of ten intraband transitions have now been determined and the decay into the yrast line has been delineated. A discussion of probable spins for the 1891-Ig superdeformed band raises questions about proposed procedures for assigning spins to superdeformed states. PACS: 23.20.Lv, 27.80.w The e:dstence of an "island" of superdeformed (SD) nuclei in the vicinity of A = 190 is now well established [1]. Among the many unanswered questions arising from the available results, those regarding the limits of the SD island in proton and neutron number and those regarding the possibility of assigning spins to the SD states have received considerable attention [1,2]. In an experiment designed for the study of superdeformation in 19~ Drigert et al. [3] found a weak SD band which was assigned to 189Hg on the basis of the available coincidence information. However, this information was rather fragmentary since, at the selected beam energy, the intensities of the measured transitions were very weak. We report here on a subsequent experiment designed to optimize the yield in the lS9Hg SD band. Additional transitions have been observed and the decay towards the yrast line has been delineated.The experiment was performed at the ATLAS superconducting linear accelerator at Argonne National Laboratory with the Argonne-Notre Dame BGO v-ray facility consisting of i2 Compton-suppressed germanium detectors (CSG) surrounding an inner array of 50 BGO ele-* Present address: GSI, W-6100 Darmstadt, Federal Republic of Germany ** Permanent address: Physics Department, Australian National University, Canberra, Australia *** Present address: Physics Department, University of Washington, Seattle, WA98195, USA ments. The 1S~ reaction at 165 MeV was selected to populate the highest spin states in lSgHg. Two stacked thin targets, totaling lmg/cm 2, of enriched (98%) 16~ were used. Only events where at least 4 array elements fired in prompt coincidence with a minimum of 2 CSG's were recorded. In the analysis, transitions between the highest-spin states were relatively enhanced by selecting V -V coincidence matrices with the condition that at least 10 of the array elements had fired. The final coincidence matrix contained approximately 10 s events.All the lines reported in ref. 3 have been observed in the present data as can be seen from fig. 1, where the sum of the spectra in coincidence with the three cleanest transitions is presented. The improved statistics results in a more precise determination of the transition energies in the SD band as well as in its extension by at least one, and more likely two, additional transitions. Furthermore, the SD v-rays are clearly in coincidence with known [4] yrast transitions in lS9Hg, some of which are indicated in fig. 1. Thus, there is no remaining uncertainty concerning the assignment of this band to lSgHg. This nucleus is the lightest Hg isotope for which superdeformati...

Model of superfluid liquid with triplet pairing, cranking model and model of variable moment of inertia in superdeformed bands inA?190 region

“…This quantity a used in [23], was taken to fit, because the experimental error bars in determination of the level energies are usually not reported. As a first illustrative example, not studied in [23], the results obtained for the recently observed [15] superdeformed band in 189Hg are given in Table 1. This case is of particular interest since it raises questions about procedures based on the methods [22,28] for assigning spins to superdeformed states.…”

Shape coexistence in neutron-deficient Hg188 investigated via lifetime measurements

“…Indeed, in the 5DCH approach a two-center basis has to be adopted for diagonalizing the Bohr Hamiltonian in order to explore the highly deformed structure [56]. Such a structure has not been observed in 188 Hg, while it is known in the neighboring 189 Hg and 190 Hg [59][60][61].…”

Systematic study of superdeformed rotational bands in Hg isotopes

“…The 190 Hg was suggested to be the lightest isotope with the SD shapes for the Hg nucleus [1]. After numerous experimental efforts [9,28], SD band in 189 Hg was assigned firmly making it the lightest Hg isotope with yrast energy spin of 14.5ÿ. The band structure of 189 Hg was analysed through particle rotor model by assuming I 0 to be 14.5ÿ and 15.5ÿ [29].…”