| 1. |
- Lv, B. F., et al.
(author)
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Evidence against the wobbling nature of low-spin bands in 135Pr
- 2022
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In: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 824
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Journal article (peer-reviewed)abstract
- The electromagnetic character of the ΔI=1 transitions connecting the 1- to 0-phonon and the 2- to 1-phonon wobbling bands should be dominated by an E2 component, due to the collective motion of the entire nuclear charge. In the present work it is shown, based on combined angular correlation and linear polarization measurements, that the mixing ratios of all analyzed connecting transitions between low-lying bands in 135Pr interpreted as 0-, 1-, and 2-phonon wobbling bands, have absolute values smaller than one. This indicates predominant M1 magnetic character, which is incompatible with the proposed wobbling nature. All experimental observables are instead in good agreement with quasiparticle-plus-triaxial-rotor model calculations, which describe the bands as resulting from a rapid re-alignment of the total angular momentum from the short to the intermediate nuclear axis.
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| 2. |
- Cederwall, Bo, 1964-, et al.
(author)
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Isospin Properties of Nuclear Pair Correlations from the Level Structure of the Self-Conjugate Nucleus Ru 88
- 2020
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In: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 124:6
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Journal article (peer-reviewed)abstract
- The low-lying energy spectrum of the extremely neutron-deficient self-conjugate (N = Z) nuclide 88Ru has been measured using the combination of the Advanced Gamma Tracking Array (AGATA)spectrometer, the NEDA, and Neutron Wall neutron detector arrays, and the DIAMANT charged particle detector array. Excited states in 88 Ru were populated via the 54 Feð 36 Ar; 2nγÞ 88 Ru fusion-evaporationreaction at the Grand Accélérateur National d’Ions Lourds (GANIL) accelerator complex. The observed γ-ray cascade is assigned to 88 Ru using clean prompt γ-γ-2-neutron coincidences in anticoincidence with the detection of charged particles, confirming and extending the previously assigned sequence of low-lying excited states. It is consistent with a moderately deformed rotating system exhibiting a band crossing at a rotational frequency that is significantly higher than standard theoretical predictions with isovector pairing, as well as observations in neighboring N > Z nuclides. The direct observation of such a “delayed” rotational alignment in a deformed N 1⁄4 Z nucleus is in agreement with theoretical predictions related to the presence of strong isoscalar neutron-proton pair correlations.
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| 3. |
- Cederwall, Bo, 1964-, et al.
(author)
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Lifetime Measurements of Excited States in Pt-172 and the Variation of Quadrupole Transition Strength with Angular Momentum
- 2018
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In: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 121:2
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Journal article (peer-reviewed)abstract
- Lifetimes of the first excited 2(+) and 4(+) states in the extremely neutron -deficient nuclide Pt-172 have been measured for the first time using the recoil-distance Doppler shift and recoil-decay tagging techniques. An unusually low value of the ratio B(E2: 4(1)(+) -> 2(1)(+)/B(E2: 2(1)(+) -> 0(gs)(+)) = 0.55(19) was found, similar to a handful of other such anomalous cases observed in the entire Segre chart. The observation adds to a cluster of a few extremely neutron -deficient nuclides of the heavy transition metals with neutron numbers N approximate to 90-94 featuring the effect. No theoretical model calculations reported to date have been able to explain the anomalously low B(E2: 4(1)(+) -> 2(1)(+)/B(E2: 2(1)(+) -> 0(gs)(+)) ratios observed in these cases. Such low values cannot, e.g., be explained within the framework of the geometrical collective model or by algebraic approaches within the interacting boson model framework. It is proposed that the group of B(E2: 4(1)(+) -> 2(1)(+)/B(E2: 2(1)(+) -> 0(gs)(+)) ratios in the extremely neutron-deficient even-even W, Os, and Pt nuclei around neutron numbers N approximate to 90-94 reveal a quantum phase transition from a seniority-conserving structure to a collective regime as a function of neutron number. Although a system governed by seniority symmetry is the only theoretical framework for which such an effect may naturally occur, the phenomenon is highly unexpected for these nuclei that are not situated near closed shells.
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| 4. |
- Ertoprak, Aysegul, et al.
(author)
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Evidence for octupole collectivity in 172Pt
- 2020
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In: European Physical Journal A. - : Springer. - 1434-6001 .- 1434-601X. ; 56:2
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Journal article (peer-reviewed)abstract
- Excited states in the extremely neutron-deficient nucleus 172Pt were populated via 96Ru(78Kr,2p) and 92Mo(83Kr,3n) reactions. The level scheme has been extended up to an excitation energy of ~ 5 MeV and tentative spin-parity assignments up to Iπ = 18+. Linear polarization and angular distribution measurements were used to determine the electromagnetic E1 character of the dipole transitions connecting the positive-parity ground-state band with an excited side-band, firmly establishing it as a negative-parity band. The lowest member of this negative-parity structure was firmly assigned spin-parity 3-. In addition, we observed an E3 transition from this 3- state to the ground state, providing direct evidence for octupole collectivity in 172Pt. Large-scale shell model (LSSM) and total Routhian surface (TRS) calculations have been performed, supporting the interpretation of the 3- state as a collective octupole-vibrational state.
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| 5. |
- Ertoprak, Aysegul, 1987-
(author)
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Experimental Studies of the Neutron Deficient Atomic Nuclei 94Ru, 95Rh and 172Pt via their Electromagnetic Properties : Du som saknar dator/datorvana kan kontakta Pär Olsson, polsson@kth.se för information
- 2020
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Doctoral thesis (other academic/artistic)abstract
- This thesis reports new results obtained from studies of the neutron deficient atomic nuclei 94Ru, 95Rh and 172Pt using two different experimental set-ups. In the first part, lifetimes of highly excited states in nuclei near the N=50 closed-shell (94Ru and 95Rh) were deduced from an analysis of the Doppler broadened transition lineshapes measured following the 58Ni(40Ca,4p) and 58Ni(40Ca,3p) fusion-evaporation reactions at the Grand Accelerateur National d'Ions Lourds (GANIL) accelerator complex situated in Caen, France. Doppler Shift Attenuation Method (DSAM) lifetime analysis was performed on the Doppler broadened peaks in energy spectra from γ-rays emitted from excited states in the nuclei of interest while they were slowing down in a thick 6 mg/cm2 metallic 58Ni target. For 94Ru, eight excited-state lifetimes in the angular momentum range I= (13-20)h have been measured in total, five of which were determined for the first time. For the lifetime analysis of 95Rh, three lifetime values have been obtained. One of them, the lifetime of the 39/21- excited state, has been measured for the first time. In the other cases, the lifetimes of the previously measured 29/22- and 37/21- excited states have been obtained. The corresponding B(M1) and B(E2) reduced transition strengths have been deduced and are discussed within the framework of large-scale shell model (LSSM) calculations. In the second part, the extremely neutron deficient 172Pt nucleus has been studied. Excited states in 172Pt were populated using the 96Ru(78Kr,2p) and 92Mo(83Kr,3n) reactions at the Accelerator Laboratory of the University of Jyväskylä (JYFL), Finland. Prompt γ-rays were detected using the JUROGAM high-purity germanium detector array at the target position while the identification and decay spectroscopy of 172Pt was performed using the RITU gas-filled separator in conjunction with the GREAT spectrometer. The Recoil Decay Tagging (RDT) technique was used for the selection of prompt γ-rays. The known positive-parity band has been extended and the negative-parity structure has been established on top of the lowest member of the negative parity band which has now been firmly assigned as spin-parity 3-. Moreover, the newly observed E3 transition provides a link between the negative parity band with the ground state. The observations of this E3 transition together with several E1 transitions connecting the negative-parity structure with the ground-state band is consistent with the presence of octupole collectivity in 172Pt. Furthermore, this is the first observation of an E3 transition connecting the negative parity band with the ground-state band in the Pt-Os-W region. The experimental results were interpreted in terms of LSSM and total routhian surface calculations. With the support of these theoretical calculations, evidence for octupole collectivity in 172Pt is proposed.
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| 6. |
- Ertoprak, Aysegul, et al.
(author)
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Lifetime measurements of core-excited states in semi-magic 95Rh
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Other publication (other academic/artistic)abstract
- Lifetimes of negative-parity states have been determined in the semi-magic (N=50) nucleus 95Rh. The fusion-evaporation reaction 58Ni(40Ca, 3p) was used to populate high-spin states in 95Rh at the Grand Accelerateur National d'Ions Lourds (GANIL) accelerator facility. The results were obtained using the Doppler Shift Attenuation Method (DSAM) based on the Doppler broadened line shapes produced during the slowing down process of the residual nuclei in a thick 6~ mg/cm2 metallic target. B(M1) and B(E2) reduced transition strengths are compared with predictions from large-scale shell-model calculations.
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| 7. |
- Ertoprak, Aysegul, 1987-
(author)
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Lifetime Measurements of Excited States in the Semi-Magic Nucleus 94Ru
- 2017
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Licentiate thesis (other academic/artistic)abstract
- Lifetimes of highly excited states in the semi-magic (N=50) nucleus 94Ru were deduced from an analysis of the Doppler broadened transition line shapes. Excited states in 94Ru were populated in the 58Ni(40Ca, 4p)94Ru∗ fusion-evaporation reaction at the Grand Accélérateur National d’Ions Lourds (GANIL) accelerator complex situated in Caen, France. Doppler Shift Attenuation Method (DSAM) lifetime analysis was performed on the Doppler broadened peaks in energy spectra from γ-rays emitted while the residual nuclei were slowing down in a thick 6 mg/cm2 metallic 58Ni target. In total eight excited-state lifetimes in the angular momentum range I = (13 − 20)ħ have been measured, five of which were determined for the first time. The deduced corresponding B(M1) and B(E2) reduced transition strengths are discussed within the framework of large-scale shell model calculations.
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| 8. |
- Ertoprak, Aysegul, et al.
(author)
-
LIFETIME MEASUREMENTS WITH THE DOPPLER SHIFT ATTENUATION METHOD USING A THICK HOMOGENEOUS PRODUCTION TARGET - VERIFICATION OF THE METHOD
- 2017
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In: Acta Physica Polonica B. - : Jagiellonian University Press. - 0587-4254 .- 1509-5770. ; 48:3, s. 325-329
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Journal article (peer-reviewed)abstract
- Doppler Shift Attenuation Method (DSAM) analysis of excited-state lifetimes normally employs thin production targets mounted on a thick stopper foil ("backing") serving to slow down and stop the recoiling nuclei of interest in a well-defined manner. Use of a thick, homogeneous production target leads to a more complex analysis as it results in a substantial decrease in the energy of the incident projectile which traverses the target with an associated change in the production cross section of the residues as a function of penetration depth. Here, a DSAM lifetime analysis using a thick homogeneous target has been verified using the Doppler broadened lineshapes of gamma rays following the decay of highly excited states in the semi-magic (N = 50) nucleus Ru-94. Lifetimes of excited states in the Ru-94 nucleus have been obtained using a modified version of the LINESHAPE package from the Doppler broadened lineshapes resulting from the emission of the gamma rays, while the residual nuclei were slowing down in the thick (6 mg/cm(2)) metallic Ni-58 target. The results have been validated by comparison with a previous measurement using a different (RDDS) technique.
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| 9. |
- Ertoprak, Aysegul, 1987-, et al.
(author)
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M1 and E2 transition rates from core-excited states in semi-magic 94Ru
-
Other publication (other academic/artistic)abstract
- Lifetimes of high-spin states have been measured in the semi-magic (N=50) nucleus 94Ru. Excited states in 94Ru were populated in the 58Ni(40Ca, 4p)94Ru∗ fusion-evaporation reaction at the Grand Accelerateur National d’Ions Lourds (GANIL) accelerator complex. DSAM lifetime analysis was performed on the Doppler broadened line shapes in energy spectra obtained from γ-rays emitted while the residual nuclei were slowing down in a thick 6 mg/cm2 metallic 58Ni target. In total eight excited-state lifetimes in the angular momentum range I = (13 − 20)ħ have been measured, five of which were determined for the first time. The deduced corresponding B(M1) and B(E2)reduced transition strengths are discussed within the framework of large-scale shell model calculations to study the contribution of different particle-hole configurations, in particular for analyzing contributions from core-excited configurations.
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| 10. |
- Ertoprak, Aysegul, et al.
(author)
-
M1 and E2 transition rates from core-excited states in semi-magic Ru-94
- 2018
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In: European Physical Journal A. - : Springer. - 1434-6001 .- 1434-601X. ; 54:9
-
Journal article (peer-reviewed)abstract
- Lifetimes of high-spin states have been measured in the semi-magic (N = 50) nucleus Ru-94. Excited states in Ru-94 were populated in the Ni-58(Ca-40, 4p)Ru-94* fusion-evaporation reaction at the Grand Accelerateur National d'Ions Lourds (GANIL) accelerator complex. DSAM lifetime analysis was performed on the Doppler broadened line shapes in energy spectra obtained from gamma-rays emitted while the residual nuclei were slowing down in a thick 6 mg/cm(2) metallic Ni-58 target. In total eight excited-state lifetimes in the angular momentum range I = (13-20)h have been measured, five of which were determined for the first time. The corresponding B(M1) and B(E2) reduced transition strengths are discussed within the framework of large-scale shell model calculations to study the contribution of different particle-hole configurations, in particular for analyzing contributions from core-excited configurations.
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