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Sökning: WFRF:(Chiara C.J.)

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1.
  • Albers, M., et al. (författare)
  • Single-particle and collective excitations in Ni 62
  • 2016
  • Ingår i: Physical Review C - Nuclear Physics. - 0556-2813. ; 94:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: Level sequences of rotational character have been observed in several nuclei in the A=60 mass region. The importance of the deformation-driving πf7/2 and νg9/2 orbitals on the onset of nuclear deformation is stressed. Purpose: A measurement was performed in order to identify collective rotational structures in the relatively neutron-rich Ni62 isotope. Method: The Mg26(Ca48,2α4nγ)Ni62 complex reaction at beam energies between 275 and 320 MeV was utilized. Reaction products were identified in mass (A) and charge (Z) with the fragment mass analyzer (FMA) and γ rays were detected with the Gammasphere array. Results: Two collective bands, built upon states of single-particle character, were identified and sizable deformation was assigned to both sequences based on the measured transitional quadrupole moments, herewith quantifying the deformation at high spin. Conclusions: Based on cranked Nilsson-Strutinsky calculations and comparisons with deformed bands in the A=60 mass region, the two rotational bands are understood as being associated with configurations involving multiple f7/2 protons and g9/2 neutrons, driving the nucleus to sizable prolate deformation.
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2.
  • Albers, M., et al. (författare)
  • Single-particle and collective excitations in Ni-63
  • 2013
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 88:5
  • Tidskriftsartikel (refereegranskat)abstract
    • A study of excited states in Ni-63 up to an excitation energy of 28 MeV and a probable spin of 57/2 was carried out with the Mg-26(Ca-48,2 alpha 3n gamma)Ni-63 reaction at beam energies between 275 and 320 MeV. Three collective bands, built upon states of single-particle character, were identified. For two of the three bands, the transition quadrupole moments were extracted, herewith quantifying the deformation at high spin. The results have been compared with shell-model and cranked Nilsson-Strutinsky calculations. Despite the Z = 28 shell closure and the approach to the purported N = 40 subshell, the Ni-63 isotope is able to sustain collective excitations at moderate and high spin.
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3.
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4.
  • Chiara, C. J., et al. (författare)
  • Probing sd-fp Cross-shell Interactions via Terminating Configurations in 42Sc,43Sc
  • 2007
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 75:5
  • Tidskriftsartikel (refereegranskat)abstract
    • An experimental study of the lower fp-shell nuclei Sc-42,Sc-43 was performed via alpha pn and alpha p evaporation, respectively, from Ne-20 + Si-28 and Mg-24 + Mg-24 fusion-evaporation reactions. The experiments were conducted with the Gammasphere and Microball detector arrays. The level schemes of both nuclei have been extended considerably. Terminating states associated with the f(7/2)(n) and d(3/2)(-1)f(7/2)(n+1) configurations were identified in each nuclide and incorporated into detailed comparisons with neighboring nuclei and with shell model calculations. The energy differences between the terminating states provide a test of the sd-fp cross-shell interactions in these calculations.
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5.
  • Henning, G., et al. (författare)
  • Exploring the stability of super heavy elements: First measurement of the fission barrier of 254No
  • 2014
  • Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. ; 66
  • Konferensbidrag (refereegranskat)abstract
    • The gamma-ray multiplicity and total energy emitted by the heavy nucleus 254No have been measured at 2 different beam energies. From these measurements, the initial distributions of spin I and excitation energy E * of 254No were constructed. The distributions display a saturation in excitation energy, which allows a direct determination of the fission barrier. 254No is the heaviest shell-stabilized nucleus with a measured fission barrier. © Owned by the authors, published by EDP Sciences, 2014.
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6.
  • Henning, G., et al. (författare)
  • Fission Barrier of Superheavy Nuclei and Persistence of Shell Effects at High Spin: Cases of No-254 and Th-220
  • 2014
  • Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 113:26
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on the first measurement of the fission barrier height in a heavy shell-stabilized nucleus. The fission barrier height of No-254 is measured to be B-f = 6.0 +/- 0.5 MeV at spin 15 (h) over bar and, by extrapolation, B-f = 6.6 +/- 0.9 MeV at spin 0 (h) over bar. This information is deduced from the measured distribution of entry points in the excitation energy versus spin plane. The same measurement is performed for Th-220 and only a lower limit of the fission barrier height can be determined: B-f (I) > 8 MeV. Comparisons with theoretical fission barriers test theories that predict properties of superheavy elements.
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7.
  • Lopez-Martens, A., et al. (författare)
  • Stability and synthesis of superheavy elements: Fighting the battle against fission - example of No-254
  • 2016
  • Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. - 9782759890118 ; 131
  • Konferensbidrag (refereegranskat)abstract
    • Superheavy nuclei exist solely due to quantum shell effects, which create a pocket in the potential-energy surface of the nucleus, thus providing a barrier against spontaneous fission. Determining the height of the fission barrier and its angular-momentum dependence is important to quantify the role that microscopic shell corrections play in enhancing and extending the limits of nuclear stability. In this talk, the first measurement of a fission barrier in the very heavy nucleus No-254 will be presented.
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8.
  • Andersson, Lise-Lotte, et al. (författare)
  • Comprehensive Gamma-ray Spectroscopy of Rotational Bands in the N=Z+1 Nucleus 61Zn
  • 2009
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 79:2
  • Tidskriftsartikel (refereegranskat)abstract
    • The Zn-61(30)31 nucleus has been studied via the combined data of two fusion-evaporation reaction experiments using a Ar-36 beam and a Si-28 target foil. The experimental setups involved the Ge array GAMMASPHERE and neutron and charged particle detectors placed around the target position. The resulting level scheme comprises about 120 excited states connected via some 180 gamma-ray transitions. In total, seven rotational structures were identified up to I similar to 25 or higher and compared with predictions from cranked Nilsson-Strutinsky calculations.
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9.
  • Andersson, Lise-Lotte, et al. (författare)
  • Extensive Gamma-ray Spectroscopy of Normally and Superdeformed Structures in 61Cu
  • 2008
  • Ingår i: European Physical Journal A. Hadrons and Nuclei. - : Springer Science and Business Media LLC. - 1434-6001. ; 36:3, s. 251-278
  • Tidskriftsartikel (refereegranskat)abstract
    • A largely extended experimental knowledge of the Cu-61(29)32 nucleus has been obtained from three experiments. Excited states in Cu-61 were produced via the fusion-evaporation reaction Si-28(Ar-36, 3p)Cu-61. In addition to the Ge array GAMMASPHERE, neutron and charged-particle detectors placed around the target position were used for high-performance particle spectroscopy. The constructed level scheme includes more than 160 energy levels and 320 gamma-ray transitions belonging to both normally deformed as well as superdeformed rotational structures. The multipolarities have been determined for the gamma-ray transitions and as a result spin-parity assignments are given for nearly all energy levels. Experimental results in the normally deformed region are compared with predictions from large-scale shell model calculations. The collective structures are compared with results from cranked Nilsson-Strutinsky calculations. The results reveal the need to modify the standard Nilsson parameters in the mass A similar to 60 region.
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10.
  • Christleib, Norbert, et al. (författare)
  • 4MOST Consortium Survey 2: The Milky Way Halo High-Resolution Survey
  • 2019
  • Ingår i: Messenger. - 0722-6691. ; 175, s. 26-29
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • We will study the formation history of the Milky Way, and the earliest phases of its chemical enrichment, with a sample of more than 1.5 million stars at high galactic latitude. Elemental abundances of up to 20 elements with a precision of better than 0.2 dex will be derived for these stars. The sample will include members of kinematically coherent substructures, which we will associate with their possible birthplaces by means of their abundance signatures and kinematics, allowing us to test models of galaxy formation. Our target catalogue is also expected to contain 30 000 stars at a metallicity of less than one hundredth that of the Sun. This sample will therefore be almost a factor of 100 larger than currently existing samples of metal-poor stars for which precise elemental abundances are available (determined from high-resolution spectroscopy), enabling us to study the early chemical evolution of the Milky Way in unprecedented detail.
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11.
  • Evans, A. O., et al. (författare)
  • Magnetic properties of deformed dipole bands in Te-110,Te-112
  • 2006
  • Ingår i: Physica Scripta. - 0031-8949. ; T125, s. 192-193
  • Tidskriftsartikel (refereegranskat)abstract
    • A lifetime analysis using the Doppler-shift attenuation method has been performed on the Tellurium isotopes Te-110,Te-112. The experiment was performed using the Gammasphere array in conjunction with the MICROBALL charged-particle detector. Three strongly coupled bands were previously established in Te-110,Te-112 which were observed up to unusually high spins. In the current experiment, it has been possible to extract lifetime measurements using a Doppler broadened lineshape analysis on one of the Delta I = 1 band structures in Te-110. In contrast to similar Delta I = 1 structures in other nuclei in this mass region, the extracted B(M1) values did not rapidly decrease with increasing angular momentum. Instead, the strongly coupled band in Te-110 represents a deformed 1p-1h structure, rather than a weakly deformed structure showing the shears mechanism.
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12.
  • Gellanki, Jnaneswari, et al. (författare)
  • Characterization of Superdeformed Bands in 62Zn
  • 2009
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 80:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Combined data from four fusion-evaporation reaction experiments were utilized to investigate deformed and superdeformed structures in Zn-62(30)32. Combination of the Gammasphere gamma-ray spectrometer and ancillary particle detection systems allowed for the connection of rotational bands to well-known, low-lying excited states in Zn-62, as well as spectroscopy of discrete high-spin states reaching excitation energies of E-x=42.5 MeV. Four well- or superdeformed bands in Zn-62 are characterized and described by means of cranked Nilsson-Strutinsky calculations.
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13.
  • Guiglion, G., et al. (författare)
  • 4MOST Survey Strategy Plan
  • 2019
  • Ingår i: Messenger. - 0722-6691. ; 175, s. 17-21
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The current status of and motivation for the 4MOST survey strategy, as developed by the Consortium science team, are presented here. Key elements of the strategy are described, such as sky coverage, number of visits and total exposure times in different parts of the sky, and how to deal with different observing conditions. The task of organising the strategy is not simple, with many different surveys that have vastly different target brightnesses and densities, sample completeness levels, and signal-to-noise requirements. We introduce here a number of concepts that we will use to ensure all surveys are optimised. Astronomers who are planning to submit a Participating Survey proposal are strongly encouraged to read this article and any relevant 4MOST Survey articles in this issue of The Messenger such that they can optimally complement and benefit from the planned surveys of the 4MOST Consortium.
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14.
  • Hartley, D. J., et al. (författare)
  • Persistence of collective behavior at high spin in the N=88 nucleus Tb-153
  • 2015
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 91:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Excited states in the N = 88 nucleus Tb-153 were observed up to spin similar to 40 in an experiment utilizing the Gammasphere array. The Tb-153 states were populated in a weak alpha 4n evaporation channel of the Cl-37 + Sn-124 reaction. Two previously known sequences were extended to higher spins, and a new decoupled structure was identified. The pi h(11/2) band was observed in the spin region where other N = 88 isotopes exhibit effects of prolate to oblate shape changes leading to band termination along the yrast line, whereas Tb-153 displays a persistent collective behavior. However, minor perturbations of the very highest state in both signatures of this h(11/2) band are observed, which perhaps signal the start of the transition towards band termination.
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15.
  • Hartley, D. J., et al. (författare)
  • Wobbling mode in Ta-167
  • 2009
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 80:4
  • Tidskriftsartikel (refereegranskat)abstract
    • The collective wobbling mode, the strongest signature for the rotation of a triaxial nucleus, has previously been seen only in a few Lu isotopes in spite of extensive searches in nearby isotopes. A sequence of transitions in the N = 94 Ta-167 nucleus exhibiting features similar to those attributed to the wobbling bands in the Lu nuclei has now been found. This band feeds into the pi i(13/2) band at a relative energy similar to that seen in the established wobbling bands and its dynamic moment of inertia and alignment properties are nearly identical to the i(13/2) structure over a significant frequency range. Given these characteristics, it is likely that the wobbling mode has been observed for the first time in a nucleus other than Lu, making this collective motion a more general phenomenon.
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16.
  • Johansson, Emma, et al. (författare)
  • Prompt Proton Decay and Deformed Bands in 56Ni
  • 2008
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 77:6
  • Tidskriftsartikel (refereegranskat)abstract
    • High-spin states in the doubly magic N=Z nucleus Ni-56 have been investigated with three fusion-evaporation reaction experiments. New gamma-ray transitions are added, and a confirmation of a previously suggested prompt proton decay from a rotational band in Ni-56 into the ground state of Co-55 is presented. The rotational bands in Ni-56 are discussed within the framework of cranked Nilsson-Strutinsky calculations.
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17.
  • Johansson, Emma, et al. (författare)
  • Prompt Proton Decay in the Vicinity of 56Ni
  • 2007
  • Ingår i: Proton Emitting Nuclei and Related Topics. - : AIP. - 1551-7616 .- 0094-243X. ; 961, s. 41-46
  • Konferensbidrag (refereegranskat)abstract
    • A new decay mode, the so called prompt proton decay, was discovered in 1998. It has since proven to be an important decay mechanism for several neutron deficient nuclei in the A similar to 60 region. To measure with high accuracy the energies and angular distributions of these protons, a state-of-the-art charged particle detector - LuWuSiA - was developed. It was first utilized during a fusion-evaporation reaction experiment performed at Argonne National Laboratory, U.S.A. In this contribution, the characteristics of the prompt proton decay are discussed along with the special features of LuWuSiA as well as a revisit to the prompt proton decay in Cu-58.
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18.
  • Johansson, Emma, et al. (författare)
  • Thorough Gamma-ray and Particle Decay Investigations of 58Ni
  • 2009
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 80:1
  • Tidskriftsartikel (refereegranskat)abstract
    • The combined data from three fusion-evaporation reaction experiments have been utilized to investigate the semi-magic nucleus Ni-58(28)30. To detect gamma rays in coincidence with evaporated particles, the Ge-detector array Gammasphere was used in conjunction with the charged-particle detectors Microball and LuWuSiA (the Lund Washington University Silicon Array), and a neutron detector array. The results yield a significantly extended level scheme of Ni-58 comprising some 340 gamma-ray transitions and include a total of at least 14 discrete particle decays into excited states of the daughter nuclei Fe-54 and Co-57. The level scheme is compared with large-scale shell-model calculations and cranked Nilsson-Strutinsky calculations.
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19.
  • LaFosse, D. R., et al. (författare)
  • Collective structures and band termination in 107Sb
  • 2000
  • Ingår i: Physical Review C - Nuclear Physics. - 0556-2813. ; 62:1
  • Tidskriftsartikel (refereegranskat)abstract
    • High-spin states in the near proton-dripline nucleus 107Sb have been identified, and collectivity in this nucleus has been observed for the first time in the form of two rotational bands. One of the observed rotational structures is a ΔI = 1 band, and is interpreted as based on a π(g9/2)-1 ⊗ π(g7/2d5/2)2 proton configuration. A second structure has ΔI = 2 character, and is explained as being based on a πh11/2⊗[π(g9/2)-2 ⊗ π(g7/2d5/2)2] proton configuration through comparison with cranked Nilsson-Strutinsky model calculations. The calculations predict that this band terminates at a spin of 79/2 (Latin small letter h with stroke).
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20.
  • Lerma, F., et al. (författare)
  • Superdeformed bands in Sr80-83, Y82-84, Zr-83,Zr-84 : Transition quadrupole moments, moments of inertia, and configuration assignments
  • 2003
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 67:4, s. 044310-
  • Tidskriftsartikel (refereegranskat)abstract
    • Multiple superdeformed bands in the nuclei Sr80-83, Y82-84, and Zr-83,Zr-84 have been studied in a backed-target experiment, using the Gammasphere and the Microball 4pi detector arrays. For 15 bands in these nuclei, average transition quadrupole moments have been measured with high accuracy, using the Doppler-shift attenuation method. Among these are the newly observed superdeformed bands in Y-83,Y-84, which are isospectral with the bands in Sr-82,Sr-83. These isospectral bands have nearly identical transition quadrupole moments. Two of the bands in Sr-81 interact and cross transitions between them are observed. The present measurements place stringent conditions on configuration assignments for the bands obtained from two types of mean-field calculations, leading to a consistent understanding of the mass similar to80 superdeformed bands. The assignments for different bands arise from one or more nucleons occupying the N-0=5h(11/2) intruder orbital.
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21.
  • Paul, E. S., et al. (författare)
  • High-spin yrast states in the gamma-soft nuclei Pr-135 and Ce-134
  • 2011
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 84:4
  • Tidskriftsartikel (refereegranskat)abstract
    • High-spin states have been studied in Pr-135(59), populated through the Cd-116(Na-23,4n) reaction at 115 MeV, using the Gammasphere gamma-ray spectrometer. The negative-parity yrast band has been significantly extended to spin similar to 45 (h) over bar and excitation energy 21.5 MeV, showing evidence for several rotational alignments. The positive-parity yrast band of Ce-135(58), populated through the p4n channel of this reaction, was also populated to spin similar to 38 (h) over bar and excitation energy 18 MeV. Cranking calculations indicate that these nuclei are soft with respect to the triaxiality parameter gamma and that several competing nuclear shapes occur at high spin.
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22.
  • Paul, E. S., et al. (författare)
  • Recent Results at Ultrahigh Spin: Terminating States and Beyond in Mass 160 Rare-earth Nuclei
  • 2015
  • Ingår i: Acta Physica Polonica. Series B: Elementary Particle Physics, Nuclear Physics, Statistical Physics, Theory of Relativity, Field Theory. - 0587-4254. ; 46:3, s. 487-496
  • Tidskriftsartikel (refereegranskat)abstract
    • A classic region of band termination at high spin occurs in rare-earth nuclei with around ten valence nucleons above the Gd-146 closed core. Results are presented here for such non-collective oblate (gamma = 60 degrees) terminating states in odd-Z Ho-155, odd-odd Ho-156, and even-even Er-156, where they are compared with neighbouring nuclei. In addition to these particularly favoured states, the occurrence of collective triaxial strongly deformed (TSD) bands, bypassing the terminating states and extending to over 65 (h) over bar, is reviewed.
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23.
  • Paul, E. S., et al. (författare)
  • Smooth terminating bands in Te-112: Particle-hole induced collectivity
  • 2007
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 75:1
  • Tidskriftsartikel (refereegranskat)abstract
    • The Gammasphere spectrometer, in conjunction with the Microball charged-particle array, was used to investigate high-spin states in Te-112 via Ni-58(Ni-58, 4p gamma) reactions at 240 and 250 MeV. Several smooth terminating bands were established, and lifetime measurements were performed for the strongest one using the Doppler-shift attenuation method. Results obtained in the spin range 18-32h yield a transition quadrupole moment of 4.0 +/- 0.5eb, which corresponds to a quadrupole deformation epsilon(2)=0.26 +/- 0.03; this value is significantly larger than the ground-state deformation of tellurium isotopes. It was also possible to extract a transition quadrupole moment for the yrast band in Xe-114, produced via the 58Ni (58Ni, 2p gamma) reaction. A value of 3.0 +/- 0.5eb was found in the spin range 16-24h, which corresponds to a quadrupole deformation epsilon(2)=0.19 +/- 0.03. Cranked Nilsson-Strutinsky calculations are used to interpret the results.
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24.
  • Radulov, D., et al. (författare)
  • beta decay of Mn-61 to levels in Fe-61
  • 2013
  • Ingår i: Physical Review C. Nuclear Physics. - : American Physical Society. - 0556-2813 .- 1089-490X. ; 88:1, s. 014307-
  • Tidskriftsartikel (refereegranskat)abstract
    • A detailed beta-decay study of Mn-61 is presented, yielding extended information on the level structure of Fe-61. Pure beams were obtained at ISOLDE, CERN, after selective laser ionization and mass separation of fission products from the bombardment of a UCx target by 1.4-GeV protons. The beta and gamma information was detected by two MiniBall clusters and three Delta E plastic scintillators. The new Mn-61 decay scheme reveals 48 gamma transitions, distributed over 20 excited states. A comparison to the decay scheme of Mn-59 and excited states in Fe-59 is made. Shell-model calculations with two different interactions are performed in order to compare the nuclear structure of the two neighboring odd-A iron isotopes. Tentative spin and parities of several excited states in Fe-61 are assigned on the basis of beta-decay feeding patterns in both Fe-59,Fe-61 and of results from the theoretical shell-model calculations.
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25.
  • Rees, J. M., et al. (författare)
  • High-spin terminating states in the N=88 Ho-155 and Er-156 isotones
  • 2015
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 91:5
  • Tidskriftsartikel (refereegranskat)abstract
    • The Sn-124(Cl-37, 6n gamma) fusion-evaporation reaction at a bombarding energy of 180 MeV has been used to significantly extend the excitation level scheme of Ho-155(67)88. The collective rotational behavior of this nucleus breaks down above spin I similar to 30 and a fully aligned noncollective (band terminating) state has been identified at I-pi = 79/2(-). Comparison with cranked Nilsson-Strutinsky calculations also provides evidence for core-excited noncollective states at I-pi = 87/2(-) and (89/2(+)) involving particle-hole excitations across the Z = 64 shell gap. A similar core-excited state in Er-156(68)88 at I-pi = (46(+)) is also presented.
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26.
  • Revill, J. P., et al. (författare)
  • Quadrupole moments of coexisting collective shapes at high spin in Er-154
  • 2013
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 88:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Four high-spin collective bands have been populated in Er-154(68)86 via the Pd-110(Ti-48, (4)n gamma)Er-154 reaction. Average transition quadrupole moments Q(t) have been measured for three of the bands by using the Doppler-shift attenuation method. The strongest band has a value of Q(t) = 11.0 +/- 1.0 e b, similar to values found recently for four triaxial strongly deformed (TSD) bands in Er-157,Er-158. The second band has a value of Q(t) = 19.5 +/- 3.2 e b, consistent with a predicted axially symmetric superdeformed (SD) shape, similar in deformation to the Dy-152 isotone, and is used as a calibration point. The third, new band has a value of Q(t) = 9.9 +/- 2.2 e b. The results confirm the unexpectedly large Q(t) moments for the favored TSD bands in light erbium isotopes.
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27.
  • Revill, J. P., et al. (författare)
  • Relative quadrupole moments of exotic shapes at ultrahigh spin in 154Er : Calibrating the TSD/SD puzzle
  • 2012
  • Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596.
  • Konferensbidrag (refereegranskat)abstract
    • Transition quadrupole moments, Qt, of two ultrahigh-spin, collective structures in 154Er have been measured for the first time using the Doppler Shift Attenuation Method (DSAM). Data were acquired at the ATLAS accelerator facility of Argonne National Laboratory, using the Gammasphere detector array. A thick, gold-backed 110Pd foil was bombarded by a beam of 48Ti ions at 215 MeV. The Qt for each band was determined from the Doppler shift of gamma rays emitted by the resulting recoil nuclei. The extracted transition quadrupole moments are significantly different in magnitude, suggesting the two structures in 154Er represent distinct exotic nuclear shapes, namely axial superdeformed (SD) with Q t 20 eb, and triaxial strongly deformed (TSD) with Qt ≈ 11 eb. Indeed, the results calibrate the quadrupole moments of TSD bands recently measured in light erbium nuclei, 157,158Er.
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28.
  • Simpson, J., et al. (författare)
  • Evolution of structure and shapes in Er 158 to ultrahigh spin
  • 2023
  • Ingår i: Physical Review C. - 2469-9985. ; 107:5
  • Tidskriftsartikel (refereegranskat)abstract
    • The level structure of Er158 has been studied using the Gammasphere spectrometer via the Cd114(Ca48,4n) reaction at 215 MeV with both thin (self-supporting) and thick (backed) targets. The level scheme has been considerably extended with more than 200 new transitions and six new rotational structures, including two strongly coupled high-K bands. Configuration assignments for the new structures are based on their observed alignments, B(M1)/B(E2) ratios of reduced transition probabilities, excitation energies, and comparisons with neighboring nuclei and theoretical calculations. With increasing angular momentum, this nucleus exhibits Coriolis-induced alignments of both neutrons and protons before it then undergoes a rotation-induced transition from near-prolate collective rotation to a noncollective oblate configuration. This transition occurs via the mechanism of band termination around spin 45ħ in three rotational structures. Two distinct lifetime branches, consistent with the crossing of a collective "fast"rotational structure by an energetically favored "slow"terminating sequence, are confirmed for the positive-parity states, and similar behavior is established in the negative-parity states. Weak-intensity, high-energy transitions are observed to feed into the terminating states. At the highest spins, three collective bands with high dynamic moments of inertia and large quadrupole moments were identified. These bands are interpreted as triaxial strongly deformed structures and mark a return to collectivity at ultrahigh spin.
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29.
  • Smith, J. F., et al. (författare)
  • Excited states and signature inversion in Cs-116
  • 2006
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 74:3, s. 034310-
  • Tidskriftsartikel (refereegranskat)abstract
    • Excited states have been observed for the first time in the very neutron-deficient, odd-odd nucleus, Cs-116(55)61. The assignment to Cs-116 has been made by the detection of gamma rays in coincidence with evaporated charged particles and with evaporation residues. The observed states form a rotational band which has been assigned to the nu(h(11/2)) circle times pi(h(11/2)) configuration. Tentative spin assignments have been made on the basis of systematic comparisons with neighboring cesium isotopes. A low-spin signature inversion is observed in the band at a rotational frequency of about 0.23 MeV/h. The observed signature inversions in the odd-odd Cs116-126 isotopes have been compared with the results of extended total Routhian surface calculations, in which signature inversion arises as a consequence of quadrupole-pairing correlations and triaxial deformation. As previously shown for some of the odd-odd A similar or equal to 120 isotopes, the calculations reproduce the signature inversions reasonably well.
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30.
  • Smith, J. F., et al. (författare)
  • Identification of excited states in 119Ba
  • 2000
  • Ingår i: Physical Review C - Nuclear Physics. - 0556-2813. ; 61:4
  • Tidskriftsartikel (refereegranskat)abstract
    • Excited states have been identified in the very neutron-deficient 119Ba nucleus. Two bands have been observed, which are likely to be based on h11/2 and (g7/2d5/2) neutron orbitals. Despite this being the first observation of excited states in 119Ba, the bands extend to (75/2)ℏ and (79/2)ℏ, respectively. The bands have been assigned to 119Ba using gamma-recoil and gamma-x-ray coincidences. Several quasiparticle alignments have been identified, involving neutron (h11/2)2 and proton (h11/2)2 aligned configurations. Furthermore, the bands show features which are reasonably consistent with smooth band termination at high spin. Theoretical results for 119Ba are discussed within the framework of cranked Woods-Saxon and Nilsson-Strutinsky calculations.
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31.
  • Starosta, K., et al. (författare)
  • Smooth band termination at high spin in 113I
  • 2001
  • Ingår i: Physical Review C - Nuclear Physics. - 0556-2813. ; 64:1, s. 143041-1430419
  • Tidskriftsartikel (refereegranskat)abstract
    • The 113I nucleus has been studied using the 58Ni(58Ni,3p) reaction at 250 MeV with the Gammasphere/ Microball facility. Gamma-ray three-and four-fold data gated by charged particle combinations were analyzed. Multipolarities of the γ rays were assigned following the angular correlation measurements. The present study is focused on the high spin properties, where the structure is dominated by 2p-2h excitations across the Z=50 gap. Ten decoupled bands showing the features of smooth band termination were observed; three of those bands are linked to known low-spin states, which allows the identification of configurations by direct comparisons with configuration-dependent cranked Nilsson-Strutinsky calculations. The yrast band, which was linked along with the signature partner, was followed up to (101/2+) and ℏω∼1.3 MeV. The other linked band was a negative-parity band observed up to (95/2-). Tentative configurations for the unlinked bands are discussed. Comparisons with the theoretical results suggest that the band built on a configuration involving the neutron i13/2 intruder orbital originating from the N=6 harmonic oscillator subshell was observed in this experiment.
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32.
  • Torres, D. A., et al. (författare)
  • Deformations and Magnetic Rotations in the 60Ni Nucleus
  • 2008
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 78:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Data from three experiments using the heavy-ion fusion evaporation-reaction Ar-36+Si-28 have been combined to study high-spin states in the residual nucleus Ni-60, which is populated via the evaporation of four protons from the compound nucleus Ge-64. The GAMMASPHERE array was used for all the experiments in conjunction with a 4 pi charged-particle detector arrays (MICROBALL, LUWUSIA) and neutron detectors (NEUTRON SHELL) to allow for the detection of. rays in coincidence with the evaporated particles. An extended Ni-60 level scheme is presented, comprising more than 270 gamma-ray transitions and 110 excited states. Their spins and parities have been assigned via directional correlations of gamma rays emitted from oriented states. Spherical shell-model calculations in the fp-shell characterize some of the low-spin states, while the experimental results of the rotational bands are analyzed with configuration-dependent cranked Nilsson-Strutinsky calculations.
  •  
33.
  • Walcher, C.~J., et al. (författare)
  • 4MOST Scientific Operations
  • 2019
  • Ingår i: Messenger. - 0722-6691. ; 175, s. 12-16
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The 4MOST instrument is a multi-object spectrograph that will address Galactic and extragalactic science cases simultaneously by observing targets from a large number of different surveys within each science exposure. This parallel mode of operation and the survey nature of 4MOST require some distinct 4MOST- specific operational features within the overall operations model of ESO. The main feature is that the 4MOST Consortium will deliver, not only the instrument, but also contractual services to the user community, which is why 4MOST is also described as a facility. This white paper concentrates on information particularly useful to answering the forthcoming Call for Letters of Intent.
  •  
34.
  • Wang, X., et al. (författare)
  • Collective structures up to spin ∼ 65h in the N 90 isotones 158Er and 157Ho
  • 2012
  • Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 381:1
  • Tidskriftsartikel (refereegranskat)abstract
    • A new collective band with high dynamic moment of inertia in 158Er at spins beyond band termination has been found in addition to the two previously reported ones. The measured transition quadrupole moments (Qt) of these three bands are very similar. These three bands have been suggested to possess a triaxial strongly deformed shape, based on comparisons with calculations using the cranked Nilsson-Strutinsky model and with tilted axis cranking calculations using the Skyrme-Hartree-Fock model. In addition, three collective bands with similar high dynamic moments of inertia, tentatively assigned to 157Ho, have been observed. Thus, it is suggested that all these structures share a common underlying character and that they are most likely associated with triaxial strongly deformed minima which are predicted to be close to the yrast line at spin 50 - 70h.
  •  
35.
  • Wang, X., et al. (författare)
  • Quadrupole moments of collective structures up to spin similar to 65(h)over-bar in Er-157 and Er-158: A challenge for understanding triaxiality in nuclei
  • 2011
  • Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 702:2-3, s. 127-130
  • Tidskriftsartikel (refereegranskat)abstract
    • The transition quadrupole moments. Q(t), of four weakly populated collective bands up to spin similar to 65h in Er-157,Er-158 have been measured to be similar to II eb demonstrating that these sequences are associated with large deformations. However, the data are inconsistent with calculated values from cranked Nilsson-Strutinsky calculations that predict the lowest energy triaxial shape to be associated with rotation about the short principal axis. The data appear to favor either a stable triaxial shape rotating about the intermediate axis or, alternatively, a triaxial shape with larger deformation rotating about the short axis. These new results challenge the present understanding of triaxiality in nuclei. (C) 2011 Elsevier B.V. All rights reserved.
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36.
  • Wilson, A. N., et al. (författare)
  • High-spin structures and alignment properties in Ce-126
  • 2001
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 6305:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Excited states in Ce-126 have been observed with the GAMMASPHERE gamma -ray detector array, used in conjunction with the MICROBALL charged-particle detector. The reaction Zn-64(Zn-64, xpn alpha) (beam energy 260 MeV) was used to populate a wide range of nuclei in the neutron-deficient region with A approximate to 120. Ce-126 was populated via the 2p evaporation channel. The three previously observed bands have been extended to higher spins and some other structures have been identified. The yrast band shows evidence of a delayed neutron alignment occurring at a rotational frequency omega approximate to0.5 MeV/(h) over bar as observed in the neighboring odd-A nucleus Pr-127. One of the two excited bands shows evidence for a similar crossing at a slightly lower frequency and also exhibits a sudden gain in alignment at omega =0.57 MeV/(h) over bar. The third band may involve the coupling of a gamma -vibrational state. All three rotational bands are discussed in terms of standard and extended cranked shell model calculations.
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