Long-lived isomers in neutron-richZ=72–76 nuclides

Abstract

A study of neutron-rich isotopes in the A = 185 region of the nuclear chart has uncovered long-lived (>1 s) isomers in several isotopes of hafnium, tantalum, tungsten, rhenium, and osmium. The region was accessed via the use of projectile fragmentation with the UNILAC-SIS accelerators at GSI. Fragmentation products of 197 Au were passed through the fragment separator (FRS) and injected into the experimental storage ring (ESR), where single-ion identifications could be made. Evidence is presented for isomers in 183,184,186 Hf, 186,187 Ta, 186 W, 190,192,194 Re, and 195 Os with excitation energies in the range of 0.1-3.0 MeV. The lightest of these nuclides have well deformed prolate shapes, while the heaviest are transitional and susceptible to shape changes. Their properties are interpreted with the help of multi-quasiparticle and potential-energy-surface calculations.

Schottky mass measurements of heavy neutron-rich nuclides in the element range70≤Z≤79at the GSI Experimental Storage Ring

“…The experiment described here was part of a larger experimental campaign, some results of which are described in Refs. [10][11][12][13]. The 197 Au beams were accelerated to the energy of 11.4 MeV/u in the linear accelerator UNILAC and then injected into the heavy ion synchrotron SIS-18 [14], where they were further accelerated to an energy of 469.35 MeV/u.…”

“…3 together with the nuclides in the ground and isomeric states identified in the other part of this exper-iment (see Refs. [10][11][12][13]).…”

Nuclear physics experiments with ion storage rings

“…For instance, a region of neutron-rich nuclei around 188 Hf is predicted to exhibit isomers with exceptional properties [70,71,72]. It was recently mapped using SMS [64,73,74,75].…”

Toward precision mass measurements of neutron-rich nuclei relevant to r-process nucleosynthesis

“…In this particular example, the carbon foil in the time-pickup detector works as an effective ∆E detector. Its total thickness amounts to roughly 300 turns × 19 µg/cm 2 /turn = 0.57 mg/cm 2 ; thus, the peaks of 51 Co 27+ and 34 Ar 18+ ions could not be completely separated from each other in the signal height distribution. A dedicated, sufficiently thick ∆E detector will certainly be helpful.…”

“…As an example, one 208 Hg nucleus was identified as a H-like ion during a two-week experiment; this mass is crucial to addressing the proton-neutron interaction strength around the doubly magic 208 Pb nucleus [48]. The sensitivity to single stored ions in SMS has been used to resolve low-lying isomeric states with excitation energies higher than about 100 keV [49][50][51][52][53].…”