Identification of high-spin proton configurations in Ba 136 and Ba 137

19 pags., 11 figs., 3 tabs.The high-spin structures of Ba136 and Ba137 are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. Ba136 is populated in a Xe136+U238 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 Be9+Te130 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 B11+Te130 fusion-evaporation reaction utilizing the HORUS γ-ray array. The level scheme above the Jπ=10+ isomer in Ba136 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 Te132 and Xe134 are characterized by high-energy 12+→10+ transitions, the Ba136E2 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 Ba137. 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.Furthermore, we express our thanks to Dr. E. Teruya and Dr. N. Yoshinaga from Saitama University, Japan, for providing the results of their shellmodel calculation with the PQM130 interaction. The research leading to these results has received funding from the German BMBF under Contracts No. 05P15PKFN9 TP1 and No. 05P18PKFN9 TP1, from the European Union Seventh Framework Programme FP7/2007-2013 under Grant Agreement No. 262010 - ENSAR, from the Spanish Ministerio de Ciencia e Innovación under Contract No. FPA2011-29854- C04, from the Spanish Ministerio de Economía y Competitividad under Contract No. FPA2014-57196-C5, and from the UK Science and Technology Facilities Council (STFC). L.K. and A.V. thank the Bonn-Cologne Graduate School of Physics and Astronomy (BCGS) for financial support. One of the authors (A. Gadea) has been supported by the Generalitat Valenciana, Spain, under Grant No. PROMETEOII/2014/019, and EU under the FEDER program

High-spin structures in Xe 132 and Xe 133 and evidence for isomers along the N=79 isotones

The transitional nuclei Xe132 and Xe133 are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. Both nuclei are populated (i) in Xe136+Pb208 MNT reactions employing the high-resolution Advanced GAmma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (ii) in the Xe136+Pt198 MNT reaction employing the GAMMASPHERE spectrometer in combination with the gas-detector array CHICO, and (iii) as an evaporation residue after a Te130(α,xn)Xe134-xn fusion-evaporation reaction employing the HORUS γ-ray array at the University of Cologne. The high-spin level schemes are considerably extended above the Jπ=(7-) and (10+) isomers in Xe132 and above the 11/2- isomer in Xe133. The results are compared to the high-spin systematics of the Z=54 as well as the N=78 and N=79 chains. Furthermore, evidence is found for a long-lived (T1/2â‰1μs) isomer in Xe133 which closes a gap along the N=79 isotones. Shell-model calculations employing the SN100PN and PQM130 effective interactions reproduce the experimental findings and provide guidance to the interpretation of the observed high-spin features

High-spin structure in the transitional nucleus 131Xe:Competitive neutron and proton alignment in the vicinity of the N = 82 shell closure

International audienceThe transitional nucleus Xe131 is investigated after multinucleon transfer in the Xe136+Pb208 and Xe136+U238 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 Sn124(B11,p3n)Xe131 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 Xe131 is extended to 5 MeV. A pronounced backbending is observed at ℏω≈0.4MeV 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 Xe129−132 provide insight into the changing nuclear structure along the Xe chain towards the N=82 shell closure. Proton occupancy in the π0h11/2 orbital is found to be decisive for the description of the observed backbending phenomenon

Lifetime measurements in the ground-state band in Pd-104

Lifetimes and reduced transition probabilities were determined in the ground-state band in Pd-104 up to the 12(+) state employing the recoil distance Doppler-shift method. Excited states were populated via the fusion-evaporation reaction Zr-96(C-12, 4n)Pd-104 at 55 MeV. The B(E2; 2(i)(+) -> O-g+s.(+)) value deviates from previous evaluated values obtained by Coulomb excitation and electron scattering. The transition strengths for higher-lying states were obtained for the first time, closing a gap in the medium-mass Pd isotope chain. Large-scale shell-model calculations were performed employing the SR88MHJM Hamiltonian along the isotope chain Pd96-106 for even-even nuclei and for high-spin states up to 26(+) in Pd-104

Lifetime measurements in Ti-44

Lifetimes of excited nuclear states were determined in Ti-44 using the recoil distance Doppler-shift technique and the Doppler-shift attenuation method. Results from the K-pi = 3(-) band confirm isospin-symmetry breaking for the 3(1)(-) -> 2(1)(+) E1 transition. The lifetime of the 4(1)(-) state differs considerably from the previously known value. Good agreement is found for the 4(1)(+) and 6(1)(+) level lifetimes with respect to previous values. The experimental values are compared with large-scale shell-model calculations employing established interactions in the 0f1p shell, as well as a modern effective Hamiltonian including multiparticle multihole cross-shell configurations. Extended configuration spaces of this shell-model calculation allow for a detailed comparison with newly determined negative-parity states

Cross-shell excitations from the f p shell: Lifetime measurements in Zn-61

Lifetimes of excited states in the neutron-deficient nucleus 61Zn were measured employing the recoil-distance Doppler-shift (RDDS) and the electronic fast-timing methods at the University of Cologne. The nucleus of interest was populated as an evaporation residue in 40Ca(24Mg,n2p)61Zn and 58Ni(α,n)61Zn reactions at 67 and 19 MeV, respectively. Five lifetimes were measured for the first time, including the lifetime of the 5/2−1 isomer at 124 keV. Short lifetimes from the RDDS analysis are corrected for Doppler-shift attenuation (DSA) in the target and stopper foils. Ambiguous observations in previous measurements were resolved. The obtained lifetimes are compared to predictions from different sets of shell-model calculations in the fp, f5/2pg9/2, and multishell fp−g9/2d5/2 model spaces. The band built on the 9/2+1 state exhibits a prolate deformation with β≈0.24. Especially, the inclusion of cross-shell excitation into the 1d5/2 orbital is found to be decisive for the description of collectivity in the first excited positive-parity band.status: publishe

Cross-shell excitations from the f p shell: Lifetime measurements in Zn-61

Lifetimes of excited states in the neutron-deficient nucleus Zn-61 were measured employing the recoil-distance Doppler-shift (RDDS) and the electronic fast-timing methods at the University of Cologne. The nucleus of interest was populated as an evaporation residue in Ca-40(Mg-24, n2p)Zn-61 and Ni-58(alpha,n)Zn-61 reactions at 67 and 19 MeV, respectively. Five lifetimes were measured for the first time, including the lifetime of the 5/2(1)(-) isomer at 124 keV. Short lifetimes from the RDDS analysis are corrected for Doppler-shift attenuation (DSA) in the target and stopper foils. Ambiguous observations in previous measurements were resolved. The obtained lifetimes are compared to predictions from different sets of shell-model calculations in the fp, f(5/2)pg(9/2), and multishell fp-g(9/2)d(5/2) model spaces. The band built on the 9/2(1)(+) state exhibits a prolate deformation with beta approximate to 0.24. Especially, the inclusion of cross-shell excitation into the 1d(5/2) orbital is found to be decisive for the description of collectivity in the first excited positive-parity band

Millisecond 23/2+ isomers in the N = 79 isotones 133Xe and 135Ba

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 (MNT) 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 9Be+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 Jπ = 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 Jπ = 23/2+ isomer with a half-life of 1.06(4) ms. The new results show a smooth onset of isomeric Jπ = 23/2+ states along the N = 79 isotones and close a gap in the high-spin systematics towards the recently investigated Jπ = 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

Millisecond 23/2+ isomers in the N = 79 isotones 133Xe and 135Ba

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 (MNT) 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 9Be+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 Jπ = 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 Jπ = 23/2+ isomer with a half-life of 1.06(4) ms. The new results show a smooth onset of isomeric Jπ = 23/2+ states along the N = 79 isotones and close a gap in the high-spin systematics towards the recently investigated Jπ = 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