| 1. |
- 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.
|
|
| 2. |
- 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.
|
|
| 3. |
- 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.
|
|
| 4. |
- Mustafa, M., et al.
(författare)
-
Diverse collective excitations in Er-159 up to high spin
- 2011
-
Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 84:5
-
Tidskriftsartikel (refereegranskat)abstract
- A spectroscopic investigation of the gamma decays from excited states in Er-159 has been performed to study the changing structural properties exhibited as ultrahigh spins (I > 60 (h) over bar) are approached. The nucleus of Er-159 was populated by the reaction Cd-116(Ca-48, 5n gamma) at a beam energy of 215 MeV, and the resulting gamma decays were studied using the Gammasphere spectrometer. New rotational bands and extensions to existing sequences were observed, which are discussed in terms of the cranked shell model, revealing a diverse range of quasiparticle configurations. At spins around 50 (h) over bar, there is evidence for a change from dominant prolate collective motion at the yrast line to oblate non-collective structures via the mechanism of band termination. A possible strongly deformed triaxial band occurs at these high spins, which indicates collectivity beyond 50 (h) over bar. The high-spin data are interpreted within the framework of cranked Nilsson-Strutinsky calculations.
|
|
| 5. |
- 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.
|
|
| 6. |
- Riley, M. A., et al.
(författare)
-
Strongly Deformed Nuclear Shapes at Ultra-High Spin and Shape Coexistence in N\sim 90 Nuclei
- 2009
-
Ingår i: Acta Physica Polonica B. - 0587-4254. ; 40:3, s. 513-522
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 7. |
- 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.
|
|
| 8. |
- Ollier, J., et al.
(författare)
-
Structure changes in Er-160 from low to ultrahigh spin
- 2011
-
Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 83:4
-
Tidskriftsartikel (refereegranskat)abstract
- A spectroscopic investigation of the gamma decays from excited states in Er-160 has been performed in order to study the changing structural properties exhibited from low spin up toward ultrahigh spin (I similar to 60 h). The nucleus Er-160 was populated by the reaction Cd-116(Ca-48,4n gamma) at a beam energy of 215 MeV, and resulting gamma decays were studied using the Gammasphere spectrometer. New rotational structures and extensions to existing bands were observed, revealing a diverse range of quasiparticle configurations, which are discussed in terms of the cranked shell model. At spins around 50h there is evidence for oblate states close to the yrast line. Three rotational bands that have the characteristics of strongly deformed triaxial structures are observed, marking a return to collectivity at even higher spin. The high-spin data are interpreted within the framework of cranked Nilsson-Strutinsky calculations.
|
|
| 9. |
- Ollier, J., et al.
(författare)
-
Ultrahigh-spin spectroscopy of Er-159,Er-160: Observation of triaxial strongly deformed structures
- 2009
-
Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 80:6
-
Tidskriftsartikel (refereegranskat)abstract
- Three weakly populated high-spin rotational bands associated with the gamma decay of Er-159 and Er-160 were observed in fusion-evaporation reactions involving a beam of Ca-48 at an energy of 215 MeV incident on a Cd-116 target. The gamma decays were detected using the highly efficient Gammasphere spectrometer. The discovery of these bands, which extend discrete-line spectroscopy in these nuclei to ultrahigh spin of similar to 60h, is consistent with recent observations of high-spin collective structures in isotopes of Er, Yb, and Tm around N=90. Cranked Nilsson-Strutinsky calculations suggest that these bands may arise from well-deformed triaxial configurations with either positive or negative gamma deformation.
|
|
| 10. |
- Riley, M A, et al.
(författare)
-
Beyond band termination in Er-157 and the search for wobbling excitations in strongly deformed Hf-174
- 2005
-
Ingår i: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 31:10, s. 1735-1740
-
Tidskriftsartikel (refereegranskat)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.
|
|
