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1.
  • Bauer, C., et al. (författare)
  • Prolate shape of Ba-140 from a first combined Doppler-shift and Coulomb-excitation measurement at the REX-ISOLDE facility
  • 2012
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 86:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: Quadrupole moments of excited nuclear states are important observables for geometrically interpreting nuclear structure in terms of deformed shapes, although data are scarce and sometimes ambiguous, in particular, in neutron-rich nuclides. Purpose: A measurement was performed for determining the spectroscopic quadrupole moment of the 2(1)(+) state of Ba-140 in order to clarify the character of quadrupole deformation (prolate or oblate) of the state in its yrast sequence of levels. Method: We have utilized a new combined technique of lifetime measurement at REX-ISOLDE and MINIBALL using the Doppler-shift attenuation method (DSAM) and a reorientation analysis of Coulomb-excitation yields. Results: On the basis of the new lifetime of tau(2(1)(+)) = 10.4(-0.8)(+2.2) ps the electric quadrupole moment was determined to be Q(2(1)(+)) = -0.52(34) eb, indicating a predominant prolate deformation. Conclusions: This finding is in agreement with beyond-mean-field calculations using the Gogny D1S force and with results from the Monte Carlo shell-model approach.
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2.
  • Hinke, C. B., et al. (författare)
  • Superallowed Gamow-Teller decay of the doubly magic nucleus 100Sn
  • 2012
  • Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 486:7403, s. 341-345
  • Tidskriftsartikel (refereegranskat)abstract
    • The shell structure of atomic nuclei is associated with 'magic numbers' and originates in the nearly independent motion of neutrons and protons in a mean potential generated by all nucleons. During beta(+)-decay, a proton transforms into a neutron in a previously not fully occupied orbital, emitting a positron-neutrino pair with either parallel or antiparallel spins, in a Gamow-Teller or Fermi transition, respectively. The transition probability, or strength, of a Gamow-Teller transition depends sensitively on the underlying shell structure and is usually distributed among many states in the neighbouring nucleus. Here we report measurements of the half-life and decay energy for the decay of Sn-100, the heaviest doubly magic nucleus with equal numbers of protons and neutrons. In the beta-decay of Sn-100, a large fraction of the strength is observable because of the large decay energy. We determine the largest Gamow-Teller strength so far measured in allowed nuclear beta-decay, establishing the 'superallowed' nature of this Gamow-Teller transition. The large strength and the low-energy states in the daughter nucleus, In-100, are well reproduced by modern, large-scale shell model calculations.
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3.
  • Schwerdtfeger, W, et al. (författare)
  • Shape Coexistence Near Neutron Number N=20 : First Identification of the E0 Decay from the Deformed First Excited J(pi)=0(+) State in Mg-30
  • 2009
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 103:1, s. 012501-
  • Tidskriftsartikel (refereegranskat)abstract
    • The 1789 keV state in Mg-30 was identified as the first excited 0(+) state via its electric monopole (E0) transition to the ground state. The measured small value of rho(2)(E0,0(2)(+)-> 0(1)(+))=(26.2 +/- 7.5)x10(-3) implies within a two-level model a small mixing of competing configurations with largely different intrinsic quadrupole deformation near the neutron shell closure at N=20. Axially symmetric configuration mixing calculations identify the ground state of Mg-30 to be based on neutron configurations below the N=20 shell closure, while the excited 0(+) state mainly consists of two neutrons excited into the nu 1f(7/2) orbital. The experimental result represents the first case where an E0 back decay from a strongly deformed second to the normal deformed first nuclear potential minimum well has been unambiguously identified, thus directly proving shape coexistence at the borderline of the much-debated "island of inversion."
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4.
  • Warr, N., et al. (författare)
  • The Miniball spectrometer
  • 2013
  • Ingår i: European Physical Journal A. Hadrons and Nuclei. - : Springer Science and Business Media LLC. - 1434-6001. ; 49:3
  • Tidskriftsartikel (refereegranskat)abstract
    • The Miniball germanium detector array has been operational at the REX (Radioactive ion beam EXperiment) post accelerator at the Isotope Separator On-Line facility ISOLDE at CERN since 2001. During the last decade, a series of successful Coulomb excitation and transfer reaction studies have been performed with this array, utilizing the unique and high-quality radioactive ion beams which are available at ISOLDE. In this article, an overview is given of the technical details of the full Miniball setup, including a description of the.-ray and particle detectors, beam monitoring devices and methods to deal with beam contamination. The specific timing properties of the REX-ISOLDE facility are highlighted to indicate the sensitivity that can be achieved with the full Miniball setup. The article is finalized with a summary of some physics highlights at REX-ISOLDE and the utilization of the Miniball germanium detectors at other facilities.
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5.
  • Ilieva, S., et al. (författare)
  • Coulomb excitation of neutron-rich Cd isotopes
  • 2014
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 89:1
  • Tidskriftsartikel (refereegranskat)abstract
    • The isotopes (122),(124),Cd-126 were studied in a "safe" Coulomb-excitation experiment at the radioactive ion-beam facility REX-ISOLDE at CERN. The reduced transition probabilities B(E2; 0(g. s)(vertical bar) -> 2(1)(+)) and limits for the quadrupole moments of the first 2(+) excited states in the three isotopes were determined. The onset of collectivity in the vicinity of the Z = 50 and N = 82 shell closures is discussed by comparison with shell model and beyond mean-field calculations.
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6.
  • Louchart, C., et al. (författare)
  • Collective nature of low-lying excitations in Zn-70,Zn-72,Zn-74 from lifetime measurements using the AGATA spectrometer demonstrator
  • 2013
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 87:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: Neutron-rich nuclei with protons in the fp shell show an onset of collectivity around N=40. Spectroscopic information is required to understand the underlying mechanism and to determine the relevant terms of the nucleon-nucleon interaction that are responsible for the evolution of the shell structure in this mass region. Methods: We report on the lifetime measurement of the first 2(+) and 4(+) states in Zn-70,Zn-72 ,Zn-74 and the first 6(+) state in Zn-72 using the recoil distance Doppler shift method. The experiment was carried out at the INFN Laboratory of Legnaro with the AGATA demonstrator, first phase of the Advanced Gamma Tracking Array of highly segmented, high-purity germanium detectors coupled to the PRISMA magnetic spectrometer. The excited states of the nuclei of interest were populated in the deep inelastic scattering of a Ge-76 beam impinging on a U-238 target. Results: The maximum of collectivity along the chain of Zn isotopes is observed for Zn-72 at N=42. An unexpectedly long lifetime of 20(-5.2)(+1.8) ps was measured for the 4(+) state in Zn-74. Conclusions: Our results lead to small values of the B(E2;4(1)(+) -> 21(+))/B(E2;2(1)(+->)0(1)(+)) ratio for Zn-72,Zn-74, suggesting a significant noncollective contribution to these excitations. These experimental results are not reproduced by state-of-the-art microscopic models and call for lifetime measurements beyond the first 2(+) state in heavy zinc and nickel isotopes.
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7.
  • Seidlitz, M., et al. (författare)
  • Coulomb excitation of Na-29,Na-30: Mapping the borders of the island of inversion
  • 2014
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 89:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Nuclear shell evolution in neutron-rich Na nuclei around N = 20 was studied by determining reduced transition probabilities, i.e., B(E2) and B(M1) values, in order to map the border of the island of inversion. To this end Coulomb-excitation experiments, employing radioactive Na-29,Na-30 beams with a final beam energy of 2.85 MeV/nucleon, were performed at REX-ISOLDE, CERN. De-excitation gamma rays were detected by the MINIBALL gamma-ray spectrometer in coincidence with scattered particles in a segmented Si detector. Transition probabilities to excited states were deduced. The measured B(E2) values agree well with shell-model predictions, supporting the idea that in the Na isotopic chain the ground-state wave function contains significant intruder admixture already at N = 18, with N = 19 having an almost pure two-particle-two-hole deformed ground-state configuration.
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8.
  • Van de Walle, J., et al. (författare)
  • Coulomb excitation of neutron-rich Zn isotopes: First observation of the 2(1)(+) state in Zn-80
  • 2007
  • Ingår i: Physical Review Letters. - 1079-7114. ; 99:14
  • Tidskriftsartikel (refereegranskat)abstract
    • Neutron-rich, radioactive Zn isotopes were investigated at the Radioactive Ion Beam facility REX-ISOLDE (CERN) using low-energy Coulomb excitation. The energy of the 2(1)(+) state in Zn-78 could be firmly established and for the first time the 2(+)-> 0(1)(+) transition in Zn-80 was observed at 1492(1) keV. B(E2,2(1)(+)-> 0(1)(+)) values were extracted for Zn-74,Zn-76,Zn-78,Zn-80 and compared to large scale shell model calculations. With only two protons outside the Z=28 proton core, Zn-80 is the lightest N=50 isotone for which spectroscopic information has been obtained to date. Two sets of advanced shell model calculations reproduce the observed B(E2) systematics. The results for N=50 isotones indicate a good N=50 shell closure and a strong Z=28 proton core polarization. The new results serve as benchmarks to establish theoretical models, predicting the nuclear properties of the doubly magic nucleus Ni-78.
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9.
  • Van de Walle, J., et al. (författare)
  • Low-energy Coulomb excitation of neutron-rich zinc isotopes
  • 2009
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 79:1
  • Tidskriftsartikel (refereegranskat)abstract
    • At the radioactive ion beam facility REX-ISOLDE, neutron-rich zinc isotopes were investigated using low-energy Coulomb excitation. These experiments have resulted in B(E2, 2(1)(+)-> 0(1)(+)) values in Zn74-80, B(E2, 4(1)(+)-> 2(1)(+)) values in Zn-74,Zn-76 and the determination of the energy of the first excited 2(1)(+) states in Zn-78,Zn-80. The zinc isotopes were produced by high-energy proton- (A = 74, 76, 80) and neutron-(A = 78) induced fission of U-238, combined with selective laser ionization and mass separation. The isobaric beam was postaccelerated by the REX linear accelerator and Coulomb excitation was induced on a thin secondary target, which was surrounded by the MINIBALL germanium detector array. In this work, it is shown how the selective laser ionization can be used to deal with the considerable isobaric beam contamination and how a reliable normalization of the experiment can be achieved. The results for zinc isotopes and the N = 50 isotones are compared to collective model predictions and state-of-the-art large-scale shell-model calculations, including a recent empirical residual interaction constructed to describe the present experimental data up to 2004 in this region of the nuclear chart.
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10.
  • Wadsworth, R., et al. (författare)
  • THE NORTHWEST FRONTIER : SPECTROSCOPY OF N similar to Z NUCLEI BELOW MASS 100
  • 2009
  • Ingår i: Acta Physica Polonica B. - 0587-4254 .- 1509-5770. ; 40:3, s. 611-620
  • Tidskriftsartikel (refereegranskat)abstract
    • The spectroscopy and structure of excited states of N similar to Z nuclei in the mass 70-100 region has been investigated using two techniques. In the A similar to 70-80 region fusion evaporation reactions coupled with the recoil-beta-tagging method have been employed at Jyvaskyla to study low-lying states in odd-odd N = Z nuclei. Results from these and other data for known odd-odd nuclei above mass 60 will be discussed. In the heavier mass 90 region a fragmentation experiment has been performed using the RIS-ING/FRS setup at GSI. This experiment was primarily aimed at searching for spin gap isomers in nuclei around A similar to 96. The objectives of the latter experiment will be discussed.
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11.
  • Boutachkov, P., et al. (författare)
  • Isomer and Beta-decay Spectroscopy of Tz=1 Isotopes Below the N=Z=50 Shell Gap
  • 2011
  • Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6596 .- 1742-6588. ; 312:9
  • Tidskriftsartikel (refereegranskat)abstract
    • The RISING setup at the GSI-FRS facility was used to investigate the isomer and beta decays in N~Z~50 Cd, Ag and Pd isotopes. A preliminary analysis of the data has revealed new results on the Tz=1, 94Pd, 96Ag and 98Cd isotopes. In 94Pd a new high-spin isomer was observed, whilst in 96Ag 3 new isomeric states were identified, including core-excited states. In 98Cd a new high-energy isomeric γ-ray transition is observed, thus enabling us to confirm the previous spin assignment for the core-excited 12+ isomer.
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12.
  • Brock, T. S., et al. (författare)
  • Observation of a new high-spin isomer in Pd-94
  • 2010
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 82:6, s. 061309-
  • Tidskriftsartikel (refereegranskat)abstract
    • A second gamma-decaying high-spin isomeric state, with a half-life of 197(22) ns, has been identified in the N = Z + 2 nuclide Pd-94 as part of a stopped-beam Rare Isotope Spectroscopic INvestigation at GSI (RISING) experiment. Weisskopf estimates were used to establish a tentative spin/parity of 19(-), corresponding to the maximum possible spin of a negative parity state in the restricted (p(1/2), g(9/2)) model space of empirical shell model calculations. The reproduction of the E3 decay properties of the isomer required an extension of the model space to include the f (5/2) and p(3/2) orbitals using the CD-Bonn potential. This is the first time that such an extension has been required for a high-spin isomer in the vicinity of Sn-100 and reveals the importance of such orbits for understanding the decay properties of high-spin isomers in this region. However, despite the need for the extended model space for the E3 decay, the dominant configuration for the 19(-) state remains (p p(1/2)(-1)g(9/2)(-3))(11)circle times(nu g(9/2)(-2))(8). The half-life of the known, 14(+), isomer was remeasured and yielded a value of 499(13) ns.
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13.
  • Chakraborty, S., et al. (författare)
  • Ground-state configuration of neutron-rich Al-35 via Coulomb breakup
  • 2017
  • Ingår i: Physical Review C. - 2469-9985 .- 2469-9993. ; 96:3, s. 1965-
  • Tidskriftsartikel (refereegranskat)abstract
    • The ground-state configuration of Al-35 has been studied via Coulomb dissociation (CD) using the LAND-FRS setup (GSI, Darmstadt) at a relativistic energy of similar to 403 MeV/nucleon. The measured inclusive differential CD cross section for Al-35, integrated up to 5.0 MeV relative energy between the Al-34 core and the neutron using a Pb target, is 78(13) mb. The exclusive measured CD cross section that populates various excited states of 34Al is 29(7) mb. The differential CD cross section of Al-35 -> Al-34 + n has been interpreted in the light of a direct breakup model, and it suggests that the possible ground-state spin and parity of Al-35 could be, tentatively, 1/2+ or 3/2(+) or 5/2(+). The valence neutrons, in the ground state of Al-35, may occupy a combination of either l = 3,0 or l = 1,2 orbitals coupled with the Al-34 core in the ground and isomeric state(s), respectively. This hints of a particle-hole configuration of the neutron across the magic shell gaps at N = 20,28 which suggests narrowing the magic shell gap. If the 5/2+ is the ground-state spin-parity of Al-35 as suggested in the literature, then the major ground-state configuration of Al-35 is a combination of Al-34(g. s.; 4(-)) circle times upsilon(p3/2) and Al-34(isomer; 1(+)) circle times upsilon(d3/2) states. The result from this experiment has been compared with that from a previous knockout measurement and a calculation using the SDPF-M interaction.
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14.
  • Chakraborty, S., et al. (författare)
  • Ground-state configuration of neutron-rich Aluminum isotopes through Coulomb breakup
  • 2014
  • Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. ; 66
  • Konferensbidrag (refereegranskat)abstract
    • Neutron-rich 34,35Al isotopes have been studied through Coulomb excitation using LAND-FRS setup at GSI, Darmstadt. The method of invariant mass analysis has been used to reconstruct the excitation energy of the nucleus prior to decay. Comparison of experimental CD cross-section with direct breakup model calculation with neutron in p3/2 orbital favours 34Al(g.s) - νp3/2 as ground state configuration of 35Al. But ground state configuration of 34Al is complicated as evident from γ-ray spectra of 33Al after Coulomb breakup of 34Al. © Owned by the authors, published by EDP Sciences, 2014.
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15.
  • Cortina-Gil, D., et al. (författare)
  • CALIFA, a Dedicated Calorimeter for the (RB)-B-3/FAIR
  • 2014
  • Ingår i: Nuclear Data Sheets. - : Elsevier BV. - 0090-3752. ; 120, s. 99-101
  • Tidskriftsartikel (refereegranskat)abstract
    • The (RB)-B-3 experiment (Reactions with Relativistic Radioactive Beams) at FAIR (Facility for Antiproton and Ion Research) is a versatile setup dedicated to the study of reactions induced by high-energy radioactive beams. It will provide kinematically complete measurements with high efficiency, acceptance and resolution, making possible a broad physics program with rare-isotopes. CALIFA (CALorimeter for In-Flight detection of gamma-rays and high energy charged pArticles), is a complex detector based on scintillation crystals, that will surround the target of the (RB)-B-3 experiment. CALIFA will act as a total absorption gamma-calorimeter and spectrometer, as well as identifier of charged particles from target residues. This versatility is its most challenging requirement, demanding a huge dynamic range, to cover from low energy gamma-rays up to 300 MeV protons. This fact, along with the high-energy of the beams determine the conceptual design of the detector, presented in this paper, together with the technical solutions proposed for its construction.
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16.
  • Hurst, A. M., et al. (författare)
  • Measurement of the sign of the spectroscopic quadrupole moment for the 2(1)(+) state in Se-70: No evidence for oblate shape
  • 2007
  • Ingår i: Physical Review Letters. - 1079-7114. ; 98:7
  • Tidskriftsartikel (refereegranskat)abstract
    • Using a method whereby molecular and atomic ions are independently selected, an isobarically pure beam of Se-70 ions was postaccelerated to an energy of 206 MeV using REX-ISOLDE. Coulomb-excitation yields for states in the beam and target nuclei were deduced by recording deexcitation gamma rays in the highly segmented MINIBALL gamma-ray spectrometer in coincidence with scattered particles in a silicon detector. At these energies, the Coulomb-excitation yield for the first 2(+) state is expected to be strongly sensitive to the sign of the spectroscopic quadrupole moment through the nuclear reorientation effect. Experimental evidence is presented here for a prolate shape for the first 2(+) state in Se-70, reopening the question over whether there are, as reported earlier, deformed oblate shapes near to the ground state in the light selenium isotopes.
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17.
  • Kroell, Th., et al. (författare)
  • Coulomb excitation of neutron-rich (138,140,142) Xe at REX-ISOLDE
  • 2007
  • Ingår i: The European Physical Journal. Special Topics. - : Springer Science and Business Media LLC. - 1951-6355 .- 1951-6401. ; 150, s. 127-129
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on "safe" Coulomb excitation of neutron-rich (138,140,142) Xe nuclei. The radioactive nuclei have been produced by ISOLDE at CERN and post-accelerated by the REX-ISOLDE facility. The gamma-rays emitted by the decay of excited states have been detected by the MINIBALL array. Recent results are presented.
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18.
  • Rahaman, A., et al. (författare)
  • Study of ground state wave-function of the Neutron-rich 29,30Na isotopes through coulomb breakup
  • 2014
  • Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. ; 66
  • Konferensbidrag (refereegranskat)abstract
    • Coulomb breakup of unstable neutron rich nuclei 29,30Na around the 'island of inversion' has been studied at energy around 434 MeV/nucleon and 409 MeV/nucleon respectively. Four momentum vectors of fragments, decay neutron from excited projectile and γ-rays emitted from excited fragments after Coulomb breakup are measured in coincidence. For these nuclei, the low-lying dipole strength above one neutron threshold can be explained by direct breakup model. The analysis for Coulomb breakup of 29,30Na shows that large amount of the cross section yields the 28Na, 29Na core in ground state. The predominant ground-state configuration of 29,30Na is found to be 28Na(g.s) νs1/2 and 29Na(g.s) νs1/2,respectively. © Owned by the authors, published by EDP Sciences, 2014.
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19.
  • Recchia, F, et al. (författare)
  • Position resolution of the prototype AGATA triple-cluster detector from an in-beam experiment
  • 2009
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 604:3, s. 555-562
  • Tidskriftsartikel (refereegranskat)abstract
    • AGATA belongs to a new generation of gamma-ray detector arrays for nuclear spectroscopy at present in its final stage of development. The detectors of these new arrays will be based on 36-fold electronically segmented coaxial germanium diodes operated in position sensitive mode. An in-beam test of the AGATA prototype triple cluster detector was carried out with the purpose of demonstrating the feasibility of such detectors and in order to measure the most sensitive parameters for their overall performance. An inverse kinematics reaction was performed, using a Ti-48 beam at an energy of 100MeV, impinging on a deuterated titanium tat-get. The results from the analysis of the experimental data, compared with the predictions of Monte Carlo Simulations, give an estimation of the position sensitivity of these detectors of about 5 mm FWHM, consistent with the specifications required. (C) 2009 Elsevier B.V. All rights reserved.
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20.
  • Seidlitz, M., et al. (författare)
  • Coulomb excitation of Mg-31
  • 2011
  • Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 700:3-4, s. 181-186
  • Tidskriftsartikel (refereegranskat)abstract
    • The ground state properties of Mg-31 indicate a change of nuclear shape at N = 19 with a deformed J(pi) = 1/2(+) intruder state as a ground state, implying that Mg-31 is part of the "island of inversion". The collective properties of excited states were the subject of a Coulomb excitation experiment at REX-ISOLDE, CERN, employing a radioactive Mg-31 beam. De-excitation gamma-rays were detected by the MINIBALL gamma-spectrometer in coincidence with scattered particles in a segmented Si-detector. The level scheme of Mg-3I was extended. Spin and parity assignment of the 945 keV state yielded 5/2(+) and its de-excitation is dominated by a strong collective M1 transition. Comparison of the transition probabilities of Mg-30,Mg-31,Mg-32 establishes that for the N = 19 magnesium isotope not only the ground state but also excited states are largely dominated by a deformed pf intruder configuration. (C) 2011 Elsevier B.V. All rights reserved.
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21.
  • Singh, B. S. Nara, et al. (författare)
  • 16(+) Spin-Gap Isomer in (96)Cd
  • 2011
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 107:17, s. 172502-
  • Tidskriftsartikel (refereegranskat)abstract
    • A beta-decaying high-spin isomer in (96)Cd, with a half-life T(1/2) = 0.29(-0.10)(+0.11) s, has been established in a stopped beam rare isotope spectroscopic investigations at GSI (RISING) experiment. The nuclei were produced using the fragmentation of a primary beam of (124)Xe on a (9)Be target. From the half-life and the observed gamma decays in the daughter nucleus, (96)Ag, we conclude that the beta-decaying state is the long predicted 16(+) "spin-gap'' isomer. Shell-model calculations, using the Gross-Frenkel interaction and the pi nu(p(1/2,)g(9/2)) model space, show that the isoscalar component of the neutron-proton interaction is essential to explain the origin of the isomer. Core excitations across the N = Z = 50 gaps and the Gamow-Teller strength, Bd(GT) distributions have been studied via large-scale shell-model calculations using the pi nu(g, d, s) model space to compare with the experimental B(GT) value obtained from the half-life of the isomer.
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22.
  • Singh, B. S. Nara, et al. (författare)
  • Influence of the np interaction on the beta decay of Pd-94
  • 2012
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 86:4, s. 041301-
  • Tidskriftsartikel (refereegranskat)abstract
    • We present results from stopped beam rare isotope spectroscopic investigations at the GSI (RISING) experiment based on the detection of gamma-ray transitions following the beta decay of Pd-94. A comparison between the measured low-lying level scheme of Rh-94 and the prediction from shell-model calculations reveals the important roles of the g(7/2) and g(9/2) orbitals in explaining the structural features. The low values of the Gamow-Teller strengths B(GT) can be attributed to the influence of the neutron-proton interaction, which gives rise to an increased seniority mixing for the nuclear states, thereby leading to a fragmentation of the strength to several daughter levels. These results provide further strong indications that Pd-94 resides in the middle of a structural transition region in the Pd isotopes as the N = Z line is approached.
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23.
  • Farrelly, G. F., et al. (författare)
  • Revision of the K-Isomer in 190W
  • 2009
  • Ingår i: Acta Physica Polonica. Series B: Elementary Particle Physics, Nuclear Physics, Statistical Physics, Theory of Relativity, Field Theory. - 0587-4254. ; 40:3, s. 885-888
  • Tidskriftsartikel (refereegranskat)abstract
    • Gamma rays from the decay of an isomer in W-190(116) have been observed following projectile fragmentation of a 1 GeV per nucleon Pb-208 beam. An earlier experiment indicated decay from a (10(-)) isomer to the ground state rotational band. Improved statistics have enabled gamma coincidence and time-difference measurements to be made which alter the previous interpretation. Blocked BCS calculations have also been used together with reduced hindrance factors to indicate possible values of spin-parity for the isomer.
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24.
  • Gorska, M., et al. (författare)
  • Nuclear Structure Addressed At GSI/RISING
  • 2009
  • Ingår i: International Journal Of Modern Physics E - Nuclear Physics. - 0218-3013. ; 18:4, s. 759-766
  • Konferensbidrag (refereegranskat)abstract
    • Nuclear structure spectroscopy studies at GSI recently gained increased momentum within a broad international community with the installation of the Rare Isotopes Spectroscopic INvestigation at GSI (RISING) project. A wide range of physical phenomena has been addressed by high-resolution in-beam gamma-ray spectroscopy experiments with radioactive beams. Relativistic radioactive beams are implanted and their subsequent. and beta decay is investigated. Within this "stopped beam campaign" germanium detectors were arranged in a close geometry around the passive stopper or an array of DSSSD detectors. The exceptionally high gamma-ray efficiency of that configuration made it possible to identify decays of excited or ground states of nuclei which have not been observed before. The results discussed here include the astrophysically relevant shell structure of N=82 isotones, N=Z nuclei around Ni-54, and proton drip-line nuclei below Sn-100. The experimental data are compared to the results of large scale shell-model calculations using various sets of realistic residual two-body interaction.
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25.
  • Podolyak, Zs., et al. (författare)
  • Weakly Deformed Oblate Structures in 198Os
  • 2009
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 79:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Gamma rays de-exciting isomeric states in the neutron-rich nucleus Os-198(76)122 have been observed following relativistic projectile fragmentation of a 1 GeV per nucleon Pb-208 beam. The ground-state band has properties compatible with oblate deformation. The evolution of the structure of Os isotopes characterized by sudden prolate-oblate shape change is discussed and contrasted with the smooth change known in the Pt chain.
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26.
  • Van de Walle, J., et al. (författare)
  • In-trap decay of Mn-61 and Coulomb excitation of Mn-61/Fe-61
  • 2009
  • Ingår i: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 42:3, s. 401-406
  • Konferensbidrag (refereegranskat)abstract
    • At ISOL ( Isotope Separator On-Line) facilities, which utilize thick primary production targets, beams of neutron-rich iron isotopes are dificult to obtain due to the long extraction time of these isotopes out of the target matrix. At REX-ISOLDE, an exploratory experiment was carried out to investigate the possibility of producing a post-accelerated beam of neutron-rich iron isotopes by the in-trap decay of neutron-rich manganese isotopes, which are available at ISOLDE using the Resonance Ionization Laser Ion Source (RILIS). This production mechanism was tested for the first time at REX-ISOLDE with an intense and short-lived beam of Mn-61 isotopes. In this work, the proof of principle of this method is demonstrated, although the technical details of the trapping process are currently not well understood and are still under investigation. The first physics results on the Coulomb excitation of Mn-61 and Fe-61 are presented and compared to shell model calculations.
  •  
27.
  • Wimmer, K., et al. (författare)
  • Identification of the slow E3 transition (136)C(s)(m)->(136)Cs with conversion electrons
  • 2011
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 84:1, s. 014329-
  • Tidskriftsartikel (refereegranskat)abstract
    • We performed at ISOLDE the spectroscopy of the decay of the 8(-) isomer in (136)Cs by. and conversion-electron detection. For the first time the excitation energy of the isomer and the multipolarity of its decay have been measured. The half-life of the isomeric state was remeasured to T(1/2) = 17.5(2) s. This isomer decays via a very slow 518-keV E3 transition to the ground state. In addition to this, a much weaker decay branch via a 413-keV M4 and a subsequent 105-keV E2 transition has been found. Thus we have found a new level at 105 keV with spin 4(+) between the isomeric and the ground state. The results are discussed in comparison to shell-model calculations.
  •  
28.
  • Diriken, J., et al. (författare)
  • Coulomb excitation of Ga-73
  • 2010
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 82:6
  • Tidskriftsartikel (refereegranskat)abstract
    • The B(E2; I-i -> I-f) values for transitions in Ga-71(31)40 and Ga-73(31)42 were deduced from a Coulomb excitation experiment at the safe energy of 2.95 MeV/nucleon using post-accelerated beams of Ga-71,Ga-73 at the REX-ISOLDE on-line isotope mass separator facility. The emitted gamma rays were detected by the MINIBALL gamma-detector array, and B(E2; I-i -> I-f) values were obtained from the yields normalized to the known strength of the 2(+) -> 0(+) transition in the Sn-120 target. The comparison of these new results with the data of less neutron-rich gallium isotopes shows a shift of the E2 collectivity toward lower excitation energy when adding neutrons beyond N = 40. This supports conclusions from previous studies of the gallium isotopes, which indicated a structural change in this isotopic chain between N = 40 and 42. Combined with recent measurements from collinear laser spectroscopy showing a 1/2(-) spin and parity for the ground state, the extracted results revealed evidence for a 1/2(-), 3/2(-) doublet near the ground state in Ga-73(31)42 differing by at most 0.8 keV in energy.
  •  
29.
  • Podolyak, Zs., et al. (författare)
  • Structure of Neutron-rich Nuclei Around the N=126 Closed Shell; the Yrast Structure of 205Au up to Spin-parity I = (19/2+)
  • 2009
  • Ingår i: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 42:3, s. 489-493
  • Konferensbidrag (refereegranskat)abstract
    • Heavy neutron-rich nuclei have been populated through the relativistic fragmentation of a Pb-208(82) beam at E/A = 1 GeV on a 2.5 g/cm(2) thick Be target. The synthesised nuclei were selected and identified in-flight using the fragment separator at GSI. Approximately 300 ns after production, the selected nuclei were implanted in an similar to 8 mm thick perspex stopper, positioned at the centre of the RISING gamma-ray detector spectrometer array. A previously unreported isomer with a half-life T-1/2 = 163(5) ns has been observed in the N = 126 closed-shell nucleus Au-205(79). Through gamma-ray singles and gamma-gamma coincidence analysis a level scheme was established. The comparison with a shell model calculation tentatively identifies the spin-parity of the excited states, including the isomer itself, which is found to be I-pi = (19/2(+)).
  •  
30.
  • Steer, S. J., et al. (författare)
  • Isomeric Decay Studies In Neutron-Rich N Approximate To 126 Nuclei
  • 2009
  • Ingår i: International Journal Of Modern Physics E-Nuclear Physics. - 0218-3013. ; 18:4, s. 1002-1007
  • Konferensbidrag (refereegranskat)abstract
    • Heavy neutron-rich nuclei were populated via relativistic energy fragmentation of a E/A= 1 GeV Pb-208 beam. The nuclei of interest were selected and identified by a fragment separator and then implanted in a passive plastic stopper. Delayed. rays following internal isomeric decays were detected by the RISING array. Experimental information was obtained on a number of nuclei with Z=73-80 (Ta-Hg), providing new information both on the prolate-oblate transitional region as well as on the N=126 closed shell nuclei.
  •  
31.
  • Steer, S. J., et al. (författare)
  • Isomeric States Observed in Heavy Neutron-rich Nuclei Populated in the Fragmentation of a 208Pb Beam
  • 2011
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 84:4
  • Tidskriftsartikel (refereegranskat)abstract
    • Heavy neutron-rich nuclei were populated via the fragmentation of a E/A = 1 GeV Pb-208(82) beam. Secondary fragments were separated and identified and subsequently implanted in a passive stopper. By the detection of delayed gamma rays, isomeric decays associated with these nuclei have been identified. A total of 49 isomers were detected, with the majority of them observed for the first time. The newly discovered isomers are in Hg-204,205(80), Au-201,202,204,205(79), Pt-197,203,204(78), Ir-195,199-203(77), Os-193,197-199(76), Re-196(75), W-190,191(74), and Ta-189(73). Possible level schemes are constructed and the structure of the nuclei discussed. To aid the interpretation, shell-model as well as BCS calculations were performed.
  •  
32.
  • Steer, S. J., et al. (författare)
  • Single-particle Behavior at N=126: Isomeric Decays in Neutron-rich 204Pt
  • 2008
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 78:6
  • Tidskriftsartikel (refereegranskat)abstract
    • The four proton-hole nucleus Pt-204 was populated in the fragmentation of an E/A = 1 GeV Pb-208 beam. The yrast structure of Pt-204 has been observed up to angular momentum I = 10h by detecting delayed gamma-ray transitions originating from metastable states. These long-lived excited states have been identified to have spin-parities of I-pi = (10(+)), (7(-)), and (5(-)) and half-lives of T-1/2 = 146(14) ns, 55(3) mu s, and 5.5(7) mu s, respectively. The structure of the magic N = 126 Pt-204 nucleus is discussed and understood in terms of the spherical shell model. The data suggest a revision of the two-body interaction for N = 126, Z < 82, which determines the evolution of nuclear structure toward the r-process waiting point nuclei.
  •  
33.
  • Stefanescu, I, et al. (författare)
  • Interplay between single-particle and collective effects in the odd-A Cu isotopes beyond N=40
  • 2008
  • Ingår i: Physical Review Letters. - 1079-7114. ; 100:11
  • Tidskriftsartikel (refereegranskat)abstract
    • Collective properties of the low-lying levels in the odd-A Cu67-73 were investigated by Coulomb excitation with radioactive beams. The beams were produced at ISOLDE and postaccelerated by REX-ISOLDE up to 2.99 MeV/u. In Cu-67,Cu-69, low-lying 1/2(-), 5/2(-), and 7/2(-) states were populated. In Cu-71,Cu-73, besides the known transitions deexciting the single-particle-like 5/2(-) and core-coupled 7/2(-) levels, gamma rays of 454 and 135 keV, respectively, were observed for the first time. Based on a reanalysis of beta-decay work and comparison with the systematics, a spin 1/2(-) is suggested for these excited states. Three B(E2) values were determined in each of the four isotopes. The results indicate a significant change in the structure of the odd-A Cu isotopes beyond N=40 where single-particle-like and collective levels are suggested to coexist at very low excitation energies.
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