| 1. |
- Reifarth, R., et al.
(author)
-
Nuclear astrophysics with radioactive ions at FAIR
- 2016
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In: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 665:1
-
Conference paper (peer-reviewed)abstract
- The nucleosynthesis of elements beyond iron is dominated by neutron captures in the s and r processes. However, 32 stable, proton-rich isotopes cannot be formed during those processes, because they are shielded from the s-process flow and r-process beta-decay chains. These nuclei are attributed to the p and rp process. For all those processes, current research in nuclear astrophysics addresses the need for more precise reaction data involving radioactive isotopes. Depending on the particular reaction, direct or inverse kinematics, forward or time-reversed direction are investigated to determine or at least to constrain the desired reaction cross sections. The Facility for Antiproton and Ion Research (FAIR) will offer unique, unprecedented opportunities to investigate many of the important reactions. The high yield of radioactive isotopes, even far away from the valley of stability, allows the investigation of isotopes involved in processes as exotic as the r or rp processes.
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| 2. |
- Grieser, M., et al.
(author)
-
Storage ring at HIE-ISOLDE Technical design report
- 2012
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In: The European Physical Journal Special Topics. - : Springer Science and Business Media LLC. - 1951-6355 .- 1951-6401. ; 207:1, s. 1-117
-
Research review (peer-reviewed)abstract
- We propose to install a storage ring at an ISOL-type radioactive beam facility for the first time. Specifically, we intend to setup the heavy-ion, low-energy ring TSR at the HIE-ISOLDE facility in CERN, Geneva. Such a facility will provide a capability for experiments with stored secondary beams that is unique in the world. The envisaged physics programme is rich and varied, spanning from investigations of nuclear ground-state properties and reaction studies of astrophysical relevance, to investigations with highly-charged ions and pure isomeric beams. The TSR might also be employed for removal of isobaric contaminants from stored ion beams and for systematic studies within the neutrino beam programme. In addition to experiments performed using beams recirculating within the ring, cooled beams can also be extracted and exploited by external spectrometers for high-precision measurements. The existing TSR, which is presently in operation at the Max-Planck Institute for Nuclear Physics in Heidelberg, is well-suited and can be employed for this purpose. The physics cases as well as technical details of the existing ring facility and of the beam and infrastructure requirements at HIE-ISOLDE are discussed in the present technical design report.
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| 3. |
- Gaffney, L. P., et al.
(author)
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Studies of pear-shaped nuclei using accelerated radioactive beams
- 2013
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In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 497:7448, s. 199-204
-
Journal article (peer-reviewed)abstract
- There is strong circumstantial evidence that certain heavy, unstable atomic nuclei are 'octupole deformed', that is, distorted into a pear shape. This contrasts with the more prevalent rugby-ball shape of nuclei with reflection-symmetric, quadrupole deformations. The elusive octupole deformed nuclei are of importance for nuclear structure theory, and also in searches for physics beyond the standard model; any measurable electric-dipole moment (a signature of the latter) is expected to be amplified in such nuclei. Here we determine electric octupole transition strengths (a direct measure of octupole correlations) for short-lived isotopes of radon and radium. Coulomb excitation experiments were performed using accelerated beams of heavy, radioactive ions. Our data on Rn-220 and Ra-224 show clear evidence for stronger octupole deformation in the latter. The results enable discrimination between differing theoretical approaches to octupole correlations, and help to constrain suitable candidates for experimental studies of atomic electric-dipole moments that might reveal extensions to the standard model.
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| 4. |
- Grieser, M., et al.
(author)
-
Storage ring at HIE-ISOLDE
- 2012
-
In: European Physical Journal: Special Topics. - : Springer Science and Business Media LLC. - 1951-6401 .- 1951-6355. ; 207:1, s. 1-117
-
Journal article (peer-reviewed)abstract
- We propose to install a storage ring at an ISOL-type radioactive beam facility for the first time. Specifically, we intend to setup the heavy-ion, low-energy ring TSR at the HIE-ISOLDE facility in CERN, Geneva. Such a facility will provide a capability for experiments with stored secondary beams that is unique in the world. The envisaged physics programme is rich and varied, spanning from investigations of nuclear ground-state properties and reaction studies of astrophysical relevance, to investigations with highly-charged ions and pure isomeric beams. The TSR might also be employed for removal of isobaric contaminants from stored ion beams and for systematic studies within the neutrino beam programme. In addition to experiments performed using beams recirculating within the ring, cooled beams can also be extracted and exploited by external spectrometers for high-precision measurements. The existing TSR, which is presently in operation at the Max-Planck Institute for Nuclear Physics in Heidelberg, is well-suited and can be employed for this purpose. The physics cases as well as technical details of the existing ring facility and of the beam and infrastructure requirements at HIE-ISOLDE are discussed in the present technical design report.
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| 5. |
- Scheck, M., et al.
(author)
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Do nuclei go pear-shaped? Coulomb excitation of Rn-220 and Ra-224 at REX-ISOLDE (CERN)
- 2015
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In: Cgs15 - Capture Gamma-ray Spectroscopy and Related Topics. - : EDP Sciences. - 2101-6275 .- 2100-014X. ; 93, s. 01038-01038
-
Conference paper (peer-reviewed)abstract
- The IS475 collaboration conducted Coulomb-excitation experiments with post-accelerated radioactive Rn-220 and Ra-224 beams at the REX-ISOLDE facility. The beam particles (E-beam: 2.83 MeV/u) were Coulomb excited using Ni-60, Cd-14, and Sn-120 scattering targets. De-excitation gamma-rays were detected employing the Miniball array and scattered particles were detected in a silicon detector. Exploiting the Coulomb-excitation code GOSIA for each nucleus several matrix elements could be obtained from the measured gamma-ray yields. The extracted < 3 parallel to E3 parallel to 0(+)> matrix element allows for the conclusion that, while Rn-220 represents an octupole vibrational system, Ra-224 has already substantial octupole correlations in its ground state. This finding has i(m)plications for the search of CP-violating Schiff moments in the atomic systems of the adjacent odd-mass nuclei.
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| 6. |
- Van de Walle, J., et al.
(author)
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Coulomb excitation of neutron-rich Zn isotopes: First observation of the 2(1)(+) state in Zn-80
- 2007
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In: Physical Review Letters. - 1079-7114. ; 99:14
-
Journal article (peer-reviewed)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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| 7. |
- de Walle, J. V., et al.
(author)
-
Coulomb excitation of the N=50 nucleus Zn-80
- 2008
-
In: AIP Conference Proceedings. - 1551-7616 .- 0094-243X. ; 1012, s. 291-295 453
-
Conference paper (peer-reviewed)abstract
- Neutron rich Zinc isotopes, including the N=50 nucleus Zn-80, were produced and post-accelerated at the Radioactive Ion Beam (RIB) facility REX-ISOLDE (CERN). Low-energy Coulomb excitation was induced on these isotopes after post-acceleration, yielding B(E2) strengths to the first excited 2(+) states. For the first time, an excited state in Zn-80 was observed and the 2(1)(+) state in Zn-78 was established. The measured B(E2,2(1)(+) -> 0(1)(+)) values are compared to two sets of large scale shell model calculations. Both calculations reproduce the observed B(E2) systematics for the full Zinc isotopic chain. 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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| 8. |
- Hurst, A. M., et al.
(author)
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Measurement of the sign of the spectroscopic quadrupole moment for the 2(1)(+) state in Se-70: No evidence for oblate shape
- 2007
-
In: Physical Review Letters. - 1079-7114. ; 98:7
-
Journal article (peer-reviewed)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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| 9. |
- Ilieva, S., et al.
(author)
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Coulomb excitation of neutron-rich Cd isotopes
- 2014
-
In: Physical Review C (Nuclear Physics). - 0556-2813. ; 89:1
-
Journal article (peer-reviewed)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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| 10. |
- Kröll, Th, et al.
(author)
-
Quadrupole Collectivity of neutron-rich nuclei around 132Sn
- 2008
-
In: Frontiers in Nuclear Structure, Astrophysics, and Reactions, FINUSTAR 2007. - : AIP. - 9780735405325 ; 1012, s. 296-299
-
Conference paper (peer-reviewed)abstract
- We report on the "safe" Coulomb excitation of neutron-rich Cd, Xe, and Ba isotopes in the vicinity of the doubly-magic nucleus 132Sn. The radioactive nuclei have been produced by ISOLDE at CERN and postaccelerated by the REX-ISOLDE facility. The γ-decay of excited states has been detected by the MINIBALL array. The presented preliminary results for the B(E2) values are consistent with expectations from phenomenological systematics and will be compared with theoretical calculations.
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| 11. |
- Polettini, M., et al.
(author)
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Decay studies in the A∼225 Po-Fr region from the DESPEC campaign at GSI in 2021
- 2022
-
In: Il Nuovo Cimento. - : Società Italiana di Fisica. - 2037-4909. ; 45:5
-
Journal article (peer-reviewed)abstract
- The HISPEC-DESPEC collaboration aims at investigating the structure of exotic nuclei formed in fragmentation reactions with decay spectroscopy measurements, as part of the FAIR Phase-0 campaign at GSI. This paper reports on first results of an experiment performed in spring 2021, with a focus on beta-decaystudies in the Po-Fr nuclei in the 220 < A <230 island of octupole deformation exploiting the DESPEC setup. Ion-beta correlations and fast-timing techniques are being employed, giving an insight into this difficult-to-reach region.
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| 12. |
- Van de Walle, J., et al.
(author)
-
Low-energy Coulomb excitation of neutron-rich zinc isotopes
- 2009
-
In: Physical Review C (Nuclear Physics). - 0556-2813. ; 79:1
-
Journal article (peer-reviewed)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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| 13. |
- Walle, J. Van de, et al.
(author)
-
Coulomb Excitation of Neutron-Rich Zn Isotopes: First Observation of the 2[sub 1][sup +] State in [sup 80]Zn
- 2007
-
In: Physical Review Letters. ; 99:14, s. 142501-
-
Journal article (peer-reviewed)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 21+ state in 78Zn could be firmly established and for the first time the 2+-->01+ transition in 80Zn was observed at 1492(1) keV. B(E2,21+-->01+) values were extracted for 74,76,78,80Zn and compared to large scale shell model calculations. With only two protons outside the Z=28 proton core, 80Zn 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 78Ni.
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| 14. |
- Warr, N., et al.
(author)
-
The Miniball spectrometer
- 2013
-
In: European Physical Journal A. Hadrons and Nuclei. - : Springer Science and Business Media LLC. - 1434-6001. ; 49:3
-
Journal article (peer-reviewed)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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| 15. |
- Hinke, C. B., et al.
(author)
-
Superallowed Gamow-Teller decay of the doubly magic nucleus 100Sn
- 2012
-
In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 486:7403, s. 341-345
-
Journal article (peer-reviewed)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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| 16. |
- Lestinsky, M., et al.
(author)
-
Physics book: CRYRING@ESR
- 2016
-
In: European Physical Journal: Special Topics. - : Springer Science and Business Media LLC. - 1951-6401 .- 1951-6355. ; 225:5, s. 797-882
-
Research review (peer-reviewed)abstract
- The exploration of the unique properties of stored and cooled beams of highly-charged ions as provided by heavy-ion storage rings has opened novel and fascinating research opportunities in the realm of atomic and nuclear physics research. Since the late 1980s, pioneering work has been performed at the CRYRING at Stockholm (Abrahamsson et al. 1993) and at the Test Storage Ring (TSR) at Heidelberg (Baumann et al. 1988). For the heaviest ions in the highest charge-states, a real quantum jump was achieved in the early 1990s by the commissioning of the Experimental Storage Ring (ESR) at GSI Helmholtzzentrum für Schwerionenforschung (GSI) in Darmstadt (Franzke 1987) where challenging experiments on the electron dynamics in the strong field regime as well as nuclear physics studies on exotic nuclei and at the borderline to atomic physics were performed. Meanwhile also at Lanzhou a heavy-ion storage ring has been taken in operation, exploiting the unique research opportunities in particular for medium-heavy ions and exotic nuclei (Xia et al. 2002).
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| 17. |
- Mucher, D., et al.
(author)
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Shell Structure and Shape Changes in Neutron Rich Krypton Isotopes
- 2009
-
In: AIP Conference Proceedings. - : AIP. - 1551-7616 .- 0094-243X. ; 1090, s. 587-588 672
-
Conference paper (peer-reviewed)abstract
- B(E2;2(1)(+) -> 0(1)(+)) values have been measured for the unstable nuclei Kr-88 (N=52) and Kr-92 (N=56) using projectile Coulomb excitation at ISOLDE, CERN. With this experiment the local maximum in E(2(1)(+)) in Kr-92 and the role of the N=56 subshell closure can be studied.
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| 18. |
- Niedermaier, O., et al.
(author)
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"Safe" Coulomb excitation of Mg-30
- 2005
-
In: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 94:17, s. 172501 (artno)-
-
Journal article (peer-reviewed)abstract
- We report on the first radioactive beam experiment performed at the recently commissioned REX-ISOLDE facility at CERN in conjunction with the highly efficient γ spectrometer MINIBALL. Using Mg-30 ions accelerated to an energy of 2.25 MeV/u together with a thin Ni-nat target, Coulomb excitation of the first excited 2(+) states of the projectile and target nuclei well below the Coulomb barrier was observed. From the measured relative deexcitation γ-ray yields the B(E2;0(gs)(+)&RARR; 2(1)(+)) value of Mg-30 was determined to be 241(31)e(2) fm(4). Our result is lower than values obtained at projectile fragmentation facilities using the intermediate-energy Coulomb excitation method, and confirms the theoretical conjecture that the neutron-rich magnesium isotope Mg-30 resides outside the "island of inversion."
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| 19. |
- Niedermaier, O., et al.
(author)
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The neutron-rich Mg isotopes: first results from MINIBALL at REX-ISOLDE
- 2005
-
In: Nuclear Physics A. - : Elsevier BV. - 0375-9474. ; 752, s. 273-273
-
Journal article (peer-reviewed)abstract
- We report on the first radioactive beam experiment performed at the recently commissioned REX-ISOLDE facility at CERN in conjunction with the highly efficient γ spectrometer MINIBALL. Using Mg-30 ions accelerated to an energy of 2.25 MeV/u together with a thin Ni-nat target, Coulomb excitation of the first excited 2(+) states of the projectile and target nuclei well below the Coulomb barrier was observed. From the measured relative deexcitation γ-ray yields the B(E2;0(gs)(+)&RARR; 2(1)(+)) value of Mg-30 was determined to be 241(31)e(2) fm(4). Our result is lower than values obtained at projectile fragmentation facilities using the intermediate-energy Coulomb excitation method, and confirms the theoretical conjecture that the neutron-rich magnesium isotope Mg-30 resides outside the "island of inversion."
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| 20. |
- Recchia, F., et al.
(author)
-
Isomer spectroscopy in odd–even Ti isotopes : Approaching n = 40
- 2019
-
In: Acta Physica Polonica B. - : Jagellonian University. - 0587-4254 .- 1509-5770. ; 50:3, s. 669-674
-
Journal article (peer-reviewed)abstract
- Our understanding of the evolution of the shell structure in nuclei far from stability is based on the study of some key nuclei. Nuclei at or next to double shell closures play a special role in this. Presently, a lot of discussion is concentrated on the neutron-rich calcium isotopes, which provide a rich testing ground for various nuclear models with several traditional and new magic numbers. 60 Ca is now almost within reach with the most advanced radioactive beam facilities. In order to investigate the evolution of the shell gap at N = 40, the configuration of states in the odd–even titanium isotopes up to N = 37 ( 59 Ti) have been studied. In order to experimentally access the shell gap at N = 40, it is nowadays within the reach of the most advanced facility the investigation of neutron hole configuration states in odd–even titanium isotopes up to N = 37, in the 59 Ti nucleus. Such states correspond to relatively simple configurations that constitute a challenging testing ground for effective nuclear interactions. The new data obtained in our experiment allows to place the present predictions concerning the shell closure at N = 40 in the calcium region on a more solid ground.
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| 21. |
- Scheit, H., et al.
(author)
-
Coulomb excitation of neutron-rich beams at REX-ISOLDE
- 2005
-
In: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-601X .- 1434-6001. ; 25:Suppl. 1, s. 397-402
-
Conference paper (peer-reviewed)abstract
- After the successful commissioning of the radioactive beam experiment at ISOLDE (REX-ISOLDE) - an accelerator for exotic nuclei produced by ISOLDE - in 2002 and the promotion to a CERN user facility in 2003, first physics experiments using these beams were performed. Initial experiments focused on the region of deformation in the vicinity of the neutron-rich Na and Mg isotopes. Preliminary results on the neutron-rich Na and Mg isotopes show the high potential and physics opportunities offered by the exotic isotope accelerator REX in conjunction with the modern Germanium gamma spectrometer MINIBALL.
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| 22. |
- Wimmer, K., et al.
(author)
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First spectroscopy of Ti-61 and the transition to the Island of Inversion at N=40
- 2019
-
In: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 792, s. 16-20
-
Journal article (peer-reviewed)abstract
- Isomeric states in Ti-59,Ti-61 have been populated in the projectile fragmentation of a 345 AMeV( 238)U beam at the Radioactive Isotope Beam Factory. The decay lifetimes and delayed gamma-ray transitions were measured with the EURICA array. Besides the known isomeric state in Ti-59, two isomeric states in Ti-61 are observed for the first time. Based on the measured lifetimes, transition multipolarities as well as tentative spins and parities are assigned. Large-scale shell model calculations based on the modified LNPS interaction show that both Ti-59 and Ti-61 belong to the Island of Inversion at N = 40 with ground state configurations dominated by particle-hole excitations to the g(9/2 )and d(5/2) orbits.
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| 23. |
- Wimmer, K., et al.
(author)
-
Isomeric states in neutron-rich nuclei near N=40
- 2021
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In: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 104:1
-
Journal article (peer-reviewed)abstract
- Neutron-rich nuclei in the vicinity of the N = 40 island of inversion are characterized by shell evolution and exhibit deformed ground states. In several nuclei isomeric states have been observed and attributed to excitations to the intruder neutron 1g(9/2) orbital. In the present paper we searched for isomeric states in nuclei around N = 40, Z = 22 produced by projectile fragmentation at the Radioactive Isotope Beam Factory. Delayed. rays were detected by the Euroball RIKEN Cluster Array germanium detector array gamma High statistics data allowed for an updated decay scheme of V-60. The lifetime of an isomeric state in V-64 was measured for the first time in the present experiment. A previously unobserved isomeric state was discovered in Sc-58. The measured lifetime suggests a parity changing transition, originating from an odd number of neutrons in the 1g(9/2) orbital. The nature of the isomeric state in Sc-58 is, thus, different from isomers in the less exotic V and Sc nuclei.
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| 24. |
- Diriken, J., et al.
(author)
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Coulomb excitation of Ga-73
- 2010
-
In: Physical Review C (Nuclear Physics). - 0556-2813. ; 82:6
-
Journal article (peer-reviewed)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.
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| 25. |
- Gaffney, L. P., et al.
(author)
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Collectivity in the light radon nuclei measured directly via Coulomb excitation
- 2015
-
In: Physical Review C (Nuclear Physics). - 0556-2813. ; 91:6
-
Journal article (peer-reviewed)abstract
- Background: Shape coexistence in heavy nuclei poses a strong challenge to state-of-the-art nuclear models, where several competing shape minima are found close to the ground state. A classic region for investigating this phenomenon is in the region around Z = 82 and the neutron midshell at N = 104. Purpose: Evidence for shape coexistence has been inferred from a-decay measurements, laser spectroscopy, and in-beam measurements. While the latter allow the pattern of excited states and rotational band structures to be mapped out, a detailed understanding of shape coexistence can only come from measurements of electromagnetic matrix elements. Method: Secondary, radioactive ion beams of Rn-202 and Rn-204 were studied by means of low-energy Coulomb excitation at the REX-ISOLDE in CERN. Results: The electric-quadrupole (E2) matrix element connecting the ground state and first excited 2(1)(+) state was extracted for both Rn-202 and Rn-204, corresponding to B(E2; 2(1)(+) -> 0(1)(+)) = 29(-8)(+8) and 43(-12)(+17) W.u., respectively. Additionally, E2 matrix elements connecting the 2(1)(+) state with the 4(1)(+) and 2(2)(+) states were determined in Rn-202. No excited 0(+) states were observed in the current data set, possibly owing to a limited population of second-order processes at the currently available beam energies. Conclusions: The results are discussed in terms of collectivity and the deformation of both nuclei studied is deduced to be weak, as expected from the low-lying level-energy schemes. Comparisons are also made to state-of-the-art beyond-mean-field model calculations and the magnitude of the transitional quadrupole moments are well reproduced.
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