The high-spin structures and isomers of the N = 81 isotones Xe-135 and Ba-137 are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. Both nuclei are populated (i) in ...Xe-136+ U-238 and (ii) Xe-136+ Pb-208 MNT reactions employing the high-resolution Advanced Gamma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (iii) in the Xe-136+ Pt-198 MNT reaction employing the gamma-ray array GAMMASPHERE in combination with the gas-detector array CHICO, and (iv) via a B-11+ Te-130 fusion-evaporation reaction with the HORUS gamma-ray array at the University of Cologne. The high-spin level schemes of Xe-135 and Ba-137 are considerably extended to higher energies. The 2058-keV (19/2(-)) state in Xe-135 is identified as an isomer, closing a gap in the systematics along the N = 81 isotones. Its half-life is measured to be 9.0(9) ns, corresponding to a reduced transition probability of B(E2,19/2(-) -> 15/2(-)) = 0.52(6) W.u. The experimentally deduced reduced transition probabilities of the isomeric states are compared to shell-model predictions. Latest shell-model calculations reproduce the experimental findings generally well and provide guidance to the interpretation of the new levels.
The high-spin structures of 136 Ba and 137 Ba are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. 136 Ba is populated in a 136 Xe + 238 U MNT reaction employing the ...high-resolution Advanced GAmma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA at the Laboratori Nazionali di Legnaro, Italy, and in two 9Be + 130 Te fusion-evaporation reactions using the High-efficiency Observatory for γ -Ray Unique Spectroscopy (HORUS) at the FN tandem accelerator of the University of Cologne, Germany. Furthermore, both isotopes are populated in an elusive reaction channel in the 11 B + 130 Te fusion-evaporation reaction utilizing the HORUS γ -ray array. The level scheme above the Jπ = 10 + isomer in 136 Ba is revised and extended up to an excitation energy of approximately 5.5 MeV. From the results of angular-correlation measurements, the Ex=3707 - and Ex=4920 -keV states are identified as the bandheads of positive- and negative-parity cascades. While the high-spin regimes of both 132 Te and 134 Xe are characterized by high-energy 12 + → 10 + transitions, the 136 Ba E 2 ground-state band is interrupted by negative-parity states only a few hundred keV above the Jπ = 10 + isomer. Furthermore, spins are established for several hitherto unassigned high-spin states in 137 Ba . The new results close a gap along the high-spin structure of N<82 Ba isotopes. Experimental results are compared to large-scale shell-model calculations employing the GCN50:82, Realistic SM, PQM130, and SN100PN interactions. The calculations suggest that the bandheads of the positive-parity bands in both isotopes are predominantly of proton character.
Detailed information on isomeric states in A ≈ 135 nuclei is exploited to benchmark shell-model calculations in the region northwest of doubly magic nucleus 132Sn. The N = 79 isotones 133Xe and 135Ba ...are studied after multinucleon transfer in the 136Xe + 208Pb reaction employing the high-resolution Advanced GAmma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA at the Laboratori Nazionali di Legnaro, Italy and in a pulsed-beam experiment at the FN tandem accelerator of the University of Cologne, Germany utilizing a 9 Be + 130Te fusion-evaporation reaction at a beam energy of 40 MeV. Isomeric states are identified via delayed γ -ray spectroscopy. Hitherto tentative excitation energy, spin, and parity assignments of the 2107-keV J π = 23/2+ isomer in 133Xe are confirmed and a half-life of T1/2 = 8.64(13) ms is measured. The 2388-keV state in 135Ba is identified as a J π = 23/2+ isomer with a half-life of 1.06(4) ms. The new results show a smooth onset of isomeric J π = 23/2+ states along the N = 79 isotones and close a gap in the high-spin systematics towards the recently investigated J π = 23/2+ isomer in 139Nd. The resulting systematics of M2 reduced transition probabilities is discussed within the framework of the nuclear shell model. Latest large-scale shell-model calculations employing the SN100PN, GCN50:82, SN100-KTH, and a realistic effective interaction reproduce the experimental findings generally well and give insight into the structure of the isomers.
The transitional nucleus 131Xe is investigated after multinucleon transfer in the 136Xe + 208Pb and 136Xe + 238U reactions employing the high-resolution Advanced γ -Tracking Array (AGATA) coupled to ...the magnetic spectrometer PRISMA at the Laboratori Nazionali di Legnaro, Italy, and as an elusive reaction product in the fusion-evaporation reaction 124Sn(11B,p3n) 131Xe employing the High-efficiency Observatory for γ -Ray Unique Spectroscopy (HORUS) γ -ray array coupled to a double-sided silicon strip detector at the University of Cologne, Germany. The level scheme of 131Xe is extended to 5 MeV. A pronounced backbending is observed at hω¯ ≈ 0.4 MeV along the negative-parity one-quasiparticle νh11/2(α = −1/2) band. The results are compared to the high-spin systematics of the Z = 54 isotopes and the N = 77 isotones. Large-scale shell-model calculations employing the PQM130, SN100PN, GCN50:82, SN100-KTH, and a realistic effective interaction reproduce the experimental findings and provide guidance to elucidate the structure of the high-spin states. Further calculations in 129−132Xe provide insight into the changing nuclear structure along the Xe chain towards the N = 82 shell closure. Proton occupancy in the π 0h11/2 orbital is found to be decisive for the description of the observed backbending phenomenon.
The even-even nucleus 142Xe lies north-east of the doubly magic 132Sn on the neutron-rich side of the nuclear chart. In order to gain further information on the octupole collectivity and the ...evolution of quadrupole collectivity in this region, a "safe" Coulomb excitation experiment was carried out at the new HIE-ISOLDE facility (CERN) at the end of 2016. As the gamma-ray detector the Miniball spectrometer was used. Beam and target nuclei were detected using C-REX, i.e. an array of segmented Si detectors, covering forward as well as backward angles in the laboratory frame.
PDF
