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

Isomers and high-spin structures in the N

The high-spin structures and isomers of the N=81 isotones 135Xe and137Ba are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. Both nuclei are populated (i) in 136 Xe+238 U and (ii) 136 Xe + 208 Pb MNT reactions employing the high-resolution Advanced Gamma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (iii) in the 136 Xe+ 198PtMNT reaction employing the γ-ray array GAMMASPHERE in combination with the gas-detector array CHICO, and (iv) via a 11 B+130Te fusion-evaporation reaction with the HORUS γ-ray array at the University of Cologne. The high-spin level schemesof 135Xe and 137 Ba are considerably extended to higher energies. The 2058-keV (19/2−) state in 135 Xe 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

Enhanced Quadrupole and Octupole Strength in Doubly Magic Sn-132

The first 2(+) and 3(-) states of the doubly magic nucleus Sn-132 are populated via safe Coulomb excitation employing the recently commissioned HIE-ISOLDE accelerator at CERN in conjunction with the highly efficient MINIBALL array. The Sn-132 ions are accelerated to an energy of 5.49 MeV/nucleon and impinged on a Pb-206 target. Deexciting gamma rays from the low-lying excited states of the target and the projectile are recorded in coincidence with scattered particles. The reduced transition strengths are determined for the transitions 0(g.s)(+) -> 2(1)(+), 0(g.s)(+) -> 3(1)(-), and 2(1)(+) -> 3(1)(-) in Sn-132. The results on these states provide crucial information on cross-shell configurations which are determined within large-scale shell-model and Monte Carlo shell-model calculations as well as from random-phase approximation and relativistic random-phase approximation. The locally enhanced B(E2; 0(g.s)(+) -> 2(1)(+)) strength is consistent with the microscopic description of the structure of the respective states within all theoretical approaches. The presented results of experiment and theory can be considered to be the first direct verification of the sphericity and double magicity of Sn-132.Peer reviewe

Enhanced collectivity along the N\ua0=\ua0Z line: Lifetime measurements in 44Ti, 48Cr, and 52Fe

Lifetimes of the 21+ states in 44Ti, 48,50Cr, and 52Fe were determined with high accuracy exploiting the recoil distance Doppler-shift method. The reduced E2 transition strengths of 44Ti and 52Fe differ considerably from previously known values. A systematic increase in collectivity is found for the N=Z nuclei compared to neighboring isotopes. The B(E2) values along the Ti, Cr, and Fe isotopic chains are compared to shell-model calculations employing established interactions for the 0f1p shell, as well as a novel effective shell-model Hamiltonian starting from a realistic nucleon\u2013nucleon potential. The theoretical approaches underestimate the B(E2) values for the lower-mass Ti isotopes. Strong indication is found for particle-hole cross-shell configurations, recently corroborated by similar results for the neighboring isotone 42Ca

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

Enhanced collectivity along the N = Z line: Lifetime measurements in44Ti,48Cr, and52Fe

Lifetimes of the 2+1states in44Ti,48,50Cr, and52Fe were determined with high accuracy exploiting the recoil distance Doppler-shift method. The reduced E2 transition strengths of44Ti and52Fe differ considerably from previously known values. A systematic increase in collectivity is found for the N = Z nuclei compared to neighboring isotopes. The B(E2) values along the Ti, Cr, and Fe isotopic chains are compared to shell-model calculations employing established interactions for the 0f1p shell, as well as a novel effective shell-model Hamiltonian starting from a realistic nucleon-nucleon potential. The theoretical approaches underestimate the B(E2) values for the lower-mass Ti isotopes. Strong indication is found for particle-hole cross-shell configurations, recently corroborated by similar results for the neighboring isotone42Ca. A detailed manuscript has meanwhile been published in Physics Letters B [1]

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