| 1. |
- Andgren, Karin, 1979-
(author)
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Studies of collective phenomena in neutron deficient nuclei : by means of lifetime measurements, angular correlation measurements and the recoil-decay tagging technique
- 2008
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Doctoral thesis (other academic/artistic)abstract
- The nucleus is a mesoscopic system that retains features from both the quantum and macroscopic worlds. A basic property of a macroscopic body is its shape. Nuclear shapes can be deduced from experimental data as they influence the excitation mode of the nucleus and hence the energies and lifetimes of its excited levels. Various short-lived nuclei were created in fusion-evaporation experiments performed at international heavy-ion accelerator facilities. The emitted γ rays and, in some experiments, also the charged particles and neutrons emitted in the reactions were detected. The studied neutron-deficient isotopes were either selected by the type and number of particles emitted in the reactions, or by using their characteristic decays. The excited states of the different isotopes were extracted from the γ-ray analyses. Spectroscopic properties, such as the lifetimes of the excited states or the angular distribution of the emitted γ rays were measured when possible. The experimentally obtained level schemes together with the other spectroscopic information were used to deduce the excitation modes and the shapes of the studied nuclei. The detector systems are described in the first chapter and in the second chapter some techniques used to extract information from the experimental data are explained. Finally, a brief theoretical overview on the nuclear models which were used to interpret the experimental results is given.
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| 2. |
- Evans, AO, et al.
(author)
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High-spin structure in Er-157 up to and above band termination
- 2006
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In: Physical Review C (Nuclear Physics). - 0556-2813. ; 73:6
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Journal article (peer-reviewed)abstract
- The high-spin structure of Er-157 has been greatly expanded using the Gammasphere spectrometer to investigate the Cd-114(Ca-48,5n) reaction at 215 MeV. Many new transitions have been placed in a greatly augmented level scheme up to spin 40h with many collective rotational sequences established. With increasing angular momentum, this nucleus undergoes a Coriolis-induced shape transition from a deformed state of collective rotation to a noncollective configuration. This transition manifests itself as favored band termination near I=45h in three rotational structures. Many weakly populated states lying at high excitation energy that decay into the terminating states have been discovered. Cranked-Nilsson-Strutinsky calculations suggest that the levels that feed the terminating states arise from weakly collective configurations that break the Z=64 semimagic core.
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| 3. |
- Evans, AO, et al.
(author)
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Magnetic properties of smooth terminating dipole bands in Te-110,Te-112
- 2006
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In: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 636:1, s. 25-30
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Journal article (peer-reviewed)abstract
- Three strongly coupled sequences have been established in Te-110,Te-112 up to high spins. They are interpreted in terms of deformed structures built on proton 1-particle-1-hole excitations that reach termination at I similar to 40h. This is the first observation of smooth terminating dipole structures in this mass region. Lifetime measurements have allowed the extraction of experimental B(M 1; 1 -> I - 1) and B(E2; I -> I - 2) reduced transition rates for one of the dipole bands in Te-110. The results support the deformed interpretation. (c) 2006 Elsevier B.V. All rights reserved.
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| 4. |
- Evans, A. O., et al.
(author)
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Magnetic properties of deformed dipole bands in Te-110,Te-112
- 2006
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In: Physica Scripta. - 0031-8949. ; T125, s. 192-193
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Journal article (peer-reviewed)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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| 5. |
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| 6. |
- Ollier, J., et al.
(author)
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Ultrahigh-spin spectroscopy of Er-159,Er-160: Observation of triaxial strongly deformed structures
- 2009
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In: Physical Review C (Nuclear Physics). - 0556-2813. ; 80:6
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Journal article (peer-reviewed)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.
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| 7. |
- Paul, E. S., et al.
(author)
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Loss of collectivity in the transitional Er-156 nucleus at high spin
- 2009
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In: Physical Review C (Nuclear Physics). - 0556-2813. ; 79:4
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Journal article (peer-reviewed)abstract
- The Cd-114(Ca-48, 6n gamma) reaction at 215 MeV has been investigated using the Gammasphere spectrometer to study the high-spin structure of the nucleus Er-156(68)88. Many new transitions have been established along with 68 definitive spin-parity level assignments from a high-fold angular-distribution analysis. In addition, absolute B(M 1) and B(E 1) strengths have been inferred from measured gamma-ray branching ratios. Strong B(E 1) strength (10(-3) W.u.) is discussed in terms of possible octupole collectivity at low spin. At high spin, this nucleus undergoes a Coriolis-induced shape transition from a prolate state of collective rotation to a noncollective, triaxial-oblate configuration. The yrast positive-parity structure ultimately terminates in an energetically favored oblate state at I-pi = 42(+). Several weak high-energy gamma-ray transitions have been discovered that feed this favored state. State-of-the-art cranked Nilsson-Strutinsky calculations are used to interpret the high-spin behavior of Er-156 and comparisons are made with other N = 88 isotones.
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| 8. |
- Paul, E. S., et al.
(author)
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Return of collective rotation in Er-157 and Er-158 at ultrahigh spin
- 2007
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In: Physical Review Letters. - 1079-7114. ; 98:1, s. 1-012501
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Journal article (peer-reviewed)abstract
- A new frontier of discrete-line gamma-ray spectroscopy at ultrahigh spin has been opened in the rare-earth nuclei Er-157,Er-158. Four rotational structures, displaying high moments of inertia, have been identified, which extend up to spin similar to 65h and bypass the band-terminating states in these nuclei which occur at similar to 45h. Cranked Nilsson-Strutinsky calculations suggest that these structures arise from well-deformed triaxial configurations that lie in a valley of favored shell energy which also includes the triaxial strongly deformed bands in Lu161-167.
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| 9. |
- Paul, E. S., et al.
(author)
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Smooth terminating bands in Te-112: Particle-hole induced collectivity
- 2007
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In: Physical Review C (Nuclear Physics). - 0556-2813. ; 75:1
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Journal article (peer-reviewed)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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| 10. |
- Paul, E. S., et al.
(author)
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The highest spin discrete levels in Ce-131,Ce-132
- 2006
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In: Physica Scripta. - 0031-8949. ; T125, s. 115-118
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Journal article (peer-reviewed)abstract
- The three superdeformed (SD) bands in Ce-132 and the two SD bands in Ce-131 have been extended to higher spin following experiments with the EUROBALL IV spectrometer. The two SD bands in 131Ce have been linked together. However, despite the relatively high population intensity of the bands ( up to 5% of the respective channel), it has not been possible to unambiguously link any of the five SD bands into the low-spin, normally deformed structures of Ce-131,Ce-132.
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