| 1. |
- Riley, M. A., et al.
(author)
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Observation of states beyond band termination in Er-156,Er-157,Er-158 and strongly deformed structures in Hf-173,Hf-174,Hf-175
- 2006
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In: Physica Scripta. - 0031-8949. ; T125, s. 123-126
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Journal article (peer-reviewed)abstract
- High-spin terminating bands in heavy nuclei were first identified in nuclei around Er-158(90). While examples of terminating states have been identified in a number of erbium isotopes, almost nothing is known about the states lying beyond band termination. In the present work, the high-spin structure of Er-156,Er-157,Er-158 has been studied using the Gammasphere spectrometer. The subject of triaxial superdeformation and 'wobbling' modes in Lu nuclei has rightly attracted a great deal of attention. Very recently four strongly or superdeformed (SD) sequences have been observed in Hf-174, and cranking calculations using the Ultimate Cranker code predict that such structures may have significant triaxial deformation. We have performed two experiments in an attempt to verify the possible triaxial nature of these bands. A lifetime measurement was performed to confirm the large (and similar) deformation of the bands. In addition, a high-statistics, thin-target experiment took place to search for linking transitions between the SD bands, possible wobbling modes, and new SD band structures.
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| 2. |
- Simpson, J., et al.
(author)
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Evolution of structure and shapes in Er 158 to ultrahigh spin
- 2023
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In: Physical Review C. - 2469-9985. ; 107:5
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Journal article (peer-reviewed)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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| 3. |
- Riley, M A, et al.
(author)
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Beyond band termination in Er-157 and the search for wobbling excitations in strongly deformed Hf-174
- 2005
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In: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 31:10, s. 1735-1740
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Journal article (peer-reviewed)abstract
- High-spin terminating bands in heavy nuclei were first identified in nuclei around Er-158(90). While examples of special terminating states have been identified in a number of erbium isotopes, almost nothing is known about the states lying beyond band termination. In the present work the high-spin structure of Er-157 has been studied using the Gammasphere spectrometer. The subject of triaxial superdeformation and 'wobbling' modes in Lu nuclei has rightly attracted a great deal of attention. Very recently, four strongly or superdeformed (SD) sequences have been observed in Hf-174 and ultimate cranker calculations predict, such structures may have significant triaxial deformation. We have performed two experiments in an attempt to verify the possible triaxial nature of these bands. A lifetime measurement was performed to confirm the large (and similar) deformation of the bands. In addition, a high-statistics, thin-target experiment was run to search for linking transitions between the SD bands and possible wobbling modes.
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| 4. |
- Al-Khatib, A, et al.
(author)
-
Transition to non-collective states at high spin in Xe-124
- 2008
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In: European Physical Journal A. Hadrons and Nuclei. - : Springer Science and Business Media LLC. - 1434-6001. ; 36:1, s. 21-29
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Journal article (peer-reviewed)abstract
- Excited states in Xe-124 were populated in the reaction Se-82(Ca-48, 6n) Xe-124 and gamma-ray coincidence relationships were measured with the Gammasphere spectrometer. Two new bands are observed and several of the previously known bands are extended in the high-as well as in the low-spin region. Two irregular high-spin structures are also added. The irregularities are a fingerprint of a transition from collective to non-collective behaviour. Configuration assignments to the new structures are proposed on the basis of systematics and by comparing experimental properties with calculations within the framework of the cranking model.
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| 5. |
- Karlgren, Daniel, et al.
(author)
-
High-angular-momentum structures in Zn-64
- 2004
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In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 69, s. 1-034330
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Journal article (peer-reviewed)abstract
- High-angular-momentum states in Zn-64 were populated in the Ca-40(Si-28,4p) reaction at a beam energy of 122 MeV. Evaporated, light, charged particles were identified by the Microball, while gamma rays were detected using the Gammasphere array. The main focus of this paper is on two strongly coupled, collective bands. The yrast band, which was previously known, has been linked to lower-lying states establishing the excitation energies and angular momenta of in-band states for the first time. The newly identified excited band decays to the yrast band but firm angular-momentum assignments could not be made. In order to interpret these structures cranked-Nilsson-Strutinsky calculations have been performed. The calculations have been extended to account for the distribution of nucleons within a configuration. The yrast collective band is interpreted as based on the pi(f(7/2))(-1)(p(3/2)f(5/2))(2)(g(9/2))(1)nu(p(3/2)f(5/2))(4)(g(9/2))(2) configuration. There are several possible interpretations of the second band but it is difficult to distinguish between the different possibilities.
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| 6. |
- Nag, Somnath, et al.
(author)
-
Collective and noncollective excitations in Te-122
- 2013
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In: Physical Review C (Nuclear Physics). - 0556-2813. ; 88:4
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Journal article (peer-reviewed)abstract
- High-spin states in Te-122 were populated in the reaction Se-82(Ca-48, alpha 4n) Te-122 at a beam energy of 200 MeV and gamma-ray coincidences weremeasured with the Gammasphere spectrometer. The previously known level scheme was extended to considerably higher spin. Maximally aligned states and several high-energy transitions feeding into some of these levels were observed. In addition, seven collective high-spin bands were discovered for the first time in this nucleus. The experimental results are compared with cranked Nilsson-Strutinsky model calculations and possible configuration assignments to the new high-spin structures are discussed.
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| 7. |
- Riley, M. A., et al.
(author)
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Strongly Deformed Nuclear Shapes at Ultra-High Spin and Shape Coexistence in N\sim 90 Nuclei
- 2009
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In: Acta Physica Polonica B. - 0587-4254. ; 40:3, s. 513-522
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Journal article (peer-reviewed)abstract
- The N similar to 90 region of the nuclear chart has featured prominently as the spectroscopy of nuclei at extreme spin has progressed. This talk will present recent discoveries from investigations of high spin behavior in the N similar to 90 Er, Tm and Yb nuclei utilizing the Gammasphere gamma-ray spectrometer. In particular it will include discussion of the beautiful shape evolution and coexistence observed in these nuclei along with the identification of a remarkable new family of band structures. The latter are very weakly populated rotational sequences with high moment of inertia that bypass the classic terminating configurations near spin 40-50 (h) over bar, marking a return to collectivity that extends discrete gamma-ray spectroscopy to well over 60 (h) over bar. Establishing the nature of the yrast states in these nuclei beyond the oblate band-termination states has been a major goal for the past two decades. Cranking calculations suggest that these new structures most likely represent stable triaxial strongly deformed bands that lie in a valley of favored shell energy in deformation and particle-number space.
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| 8. |
- Singh, Purnima, et al.
(author)
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Highly deformed high-spin band in I-125
- 2011
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In: Physical Review C (Nuclear Physics). - 0556-2813. ; 84:2
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Journal article (peer-reviewed)abstract
- High-spin states in I-125 have been investigated using the reaction Se-82(Ca-48, p4n) at a beam energy of 200 MeV and gamma-ray coincidence events were detected using the Gammasphere spectrometer. A deformed rotational band, extending up to I-pi = 95/2(-), was observed for the first time in a heavier odd-A iodine nucleus. The characteristics of the band are very similar to those of the highly deformed bands observed recently in neighboring nuclei and it is essentially identical to one of the previously known bands in Xe-126. The experimental results are compared to cranked Nilsson-Strutinsky calculations and possible configurations for the band are discussed.
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| 9. |
- Singh, Purnima, et al.
(author)
-
Noncollective aligned and antialigned states in I-125
- 2010
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In: Physical Review C (Nuclear Physics). - 0556-2813. ; 82:3
-
Journal article (peer-reviewed)abstract
- High-spin states in I-125 were populated using the reaction Se-82(Ca-48, p4n) at a beam energy of 200 MeV and gamma-ray coincidence events were acquired with the Gammasphere spectrometer. The level scheme of I-125 was extended considerably. In particular, maximally aligned states involving all eleven particles outside the Sn-114 core were observed. Comparison with cranked Nilsson-Strutinsky calculations suggests that three of these states are the final I-max states in terminating bands with all spin vectors aligned along a common axis. In two of these, one spin vector is antialigned and points in the opposite direction. In one of the states two spin vectors are antialigned. This is the first observation of a state with such a structure.
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| 10. |
- Lauritsen, T., et al.
(author)
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Characterization of a gamma-ray tracking array : A comparison of GRETINA and Gammasphere using a 60Co source
- 2016
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In: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002. ; 836, s. 46-56
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Journal article (peer-reviewed)abstract
- In this paper, we provide a formalism for the characterization of tracking arrays with emphasis on the proper corrections required to extract their photopeak efficiencies and peak-to-total ratios. The methods are first applied to Gammasphere, a well characterized 4π array based on the principle of Compton suppression, and subsequently to GRETINA. The tracking efficiencies are then discussed and some guidelines as to what clustering angle to use in the tracking algorithm are presented. It was possible, using GEANT4 simulations, to scale the measured efficiencies up to the expected values for the full 4π implementation of GRETA.
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