| 1. |
- Andreoiu, Corina, et al.
(författare)
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Doorway States in the Gamma Decay-out of the Yrast Superdeformed Band in 59Cu
- 2003
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Ingår i: Physical Review Letters. - 1079-7114. ; 91:23
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Tidskriftsartikel (refereegranskat)abstract
- The decay-out process of the yrast superdeformed band in Cu-59 has been investigated. The firm determination of spin, parity, excitation energy, and configuration of the states involved in this process constitutes a unique situation for a detailed understanding of the decay-out mechanism. A theoretical model is introduced that includes a residual interaction and tunneling matrix element between bands, calculated in the configuration-dependent cranked Nilsson-Strutinsky model. This interaction causes the decay to occur via a small number of observed doorway states.
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| 2. |
- Karlgren, Daniel, et al.
(författare)
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High-angular-momentum structures in Zn-64
- 2004
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Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 69, s. 1-034330
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Ma, W. C., et al.
(författare)
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Competition between terminating and collective structures above spin 40ℏ in 154Dy
- 2002
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Ingår i: Physical Review C - Nuclear Physics. - 0556-2813. ; 65, s. 1-034312
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Tidskriftsartikel (refereegranskat)abstract
- High-spin states in 154Dy were studied with the Gammasphere spectrometer using the 36S(122Sn,4n) reaction. Band terminating states were identified in the spin range I= (36-48)ℏ, and were found to compete with collective rotational cascades up to the highest observed spins. Several "sidebands" feeding the terminating structures were identified as well. A band dominated by M1 transitions was observed to terminate at Iπ = 42-. The data are interpreted within the framework of configuration-dependent cranked Nilsson-Strutinsky calculations without pairing.
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| 4. |
- Pasqualato, G., et al.
(författare)
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Shape evolution in even-mass 98-104Zr isotopes via lifetime measurements using the γ γ-coincidence technique
- 2023
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Ingår i: European Physical Journal A. - : Springer. - 1434-6001 .- 1434-601X. ; 59:11
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Tidskriftsartikel (refereegranskat)abstract
- The Zirconium (Z = 40) isotopic chain has attracted interest for more than four decades. The abrupt lowering of the energy of the first 2(+) state and the increase in the transition strength B(E2; 2(1)(+) -> 0(1)(+) ) going from Zr-98 to Zr-100 has been the first example of "quantum phase transition" in nuclear shapes, which has few equivalents in the nuclear chart. Although a multitude of experiments have been performed to measure nuclear properties related to nuclear shapes and collectivity in the region, none of the measured lifetimes were obtained using the Recoil Distance Doppler Shift method in the gamma gamma-coincidence mode where a gate on the direct feeding transition of the state of interest allows a strict control of systematical errors. This work reports the results of lifetime measurements for the first yrast excited states in Zr98-104 carried out to extract reduced transition probabilities. The new lifetime values in gamma gamma-coincidence and gamma-single mode are compared with the results of former experiments. Recent predictions of the Interacting Boson Model with Configuration Mixing, the Symmetry Conserving Configuration Mixing model based on the Hartree-Fock- Bogoliubov approach and the Monte Carlo Shell Model are presented and compared with the experimental data.
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| 5. |
- Riley, M. A., et al.
(författare)
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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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Ingår i: Physica Scripta. - 0031-8949. ; T125, s. 123-126
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Tidskriftsartikel (refereegranskat)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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| 6. |
- Simpson, J., et al.
(författare)
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Evolution of structure and shapes in Er 158 to ultrahigh spin
- 2023
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Ingår i: Physical Review C. - 2469-9985. ; 107:5
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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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| 7. |
- Andreoiu, Corina, et al.
(författare)
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Evolution of Shapes in 59Cu
- 2002
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Ingår i: European Physical Journal A. Hadrons and Nuclei. - : Springer Science and Business Media LLC. - 1434-6001. ; 14:3, s. 317-348
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Tidskriftsartikel (refereegranskat)abstract
- High-spin states in Cu-59 were populated using the fusion-evaporation reaction Si-28 + Ca-40 at a beam energy of 122 MeV. The Gammasphere Ge-detector array in conjunction with the 4pi charged-particle detector array Microball allowed for the detection of gamma-rays in coincidence with evaporated light particles. The resulting extensive high-spin decay scheme of Cu-59 is presented, which comprises more than 320 gamma-ray transitions connecting about 150 excited states. Their spins and parities have been assigned via directional correlations of gamma-rays emitted from oriented states. Average quadrupole moments of rotational bands have been determined from the analysis of residual Doppler shifts. Shell model calculations in the fp shell are invoked to study some of the low-spin states, while the experimental characteristics of the rotational bands are analyzed in the configuration-dependent cranked Nilsson-Strutinsky (CNS) approach.
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| 8. |
- Andreyev, A. N., et al.
(författare)
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α decay of the neutron-deficient isotope 190At
- 2023
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Ingår i: Physical Review C. - 2469-9985. ; 108:3
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Tidskriftsartikel (refereegranskat)abstract
- The α decay of the neutron-deficient 190At isotope was observed following the 103Rh(90Zr,3n)190At reaction at Argonne National Laboratory. The reaction products were separated from the beam using the Argonne Gas-Filled Analyzer and implanted into a double-sided Si strip detector. The spatial and temporal correlations between implanted nuclei and subsequent α decays towards the known daughter isotope 186Bi were used to identify and characterize 190At nuclei. Two possible decay scenarios are proposed for the 190At→186Bi decay.
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| 9. |
- Døssing, T, et al.
(författare)
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Decay-Out Of Superdeformed Bands By Coupling To Ordered Or Chaotic Spectra
- 2005
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Ingår i: AIP Conference Proceedings. - : AIP. - 0094-243X. ; 764:1, s. 27-33
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Tidskriftsartikel (refereegranskat)abstract
- Different treatments of the decay-out of superdeformed bands are reviewed, focusing on the role of the normally deformed doorway states to which the superdeformed band primarily couples at decay-out. A schematic description based on sparse GOE matrices is formulated for the normally deformed states including one doorway state. This allows for a gradual change of the normally deformed spectrum from an ordered to a chaotic situation by means of the effective dimensionality parameter. It is found that the distribution of the small normally deformed admixtures into the superdeformed band, through which it decays, depends sensitively on the effective dimensionality parameter. Analyzing the measured distribution of transition strength of decay-out gamma-ray lines in 194Hg, it is concluded that the spectrum of normally deformed states is closer to the chaotic than the ordered situation at the energy and angular momentum of the superdeformed band. ©2005 American Institute of Physics
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| 10. |
- Døssing, T, et al.
(författare)
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Order to Chaos Properties of the Decay-out Gamma Rays from Superdeformed Bands
- 2004
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Ingår i: AIP Conference Proceedings. - : AIP. - 0094-243X. ; 701, s. 164-168
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Tidskriftsartikel (refereegranskat)abstract
- Based on GOE sparse matrices, a model for decay-out of superdeformed bands is formulated, with focus on the degree of chaoticity of the spectrum of normally deformed states, to which the superdeformed band couples at decay-out. By means of the effective dimensionality parameter, the spectrum may be varied between the two limiting situations of complete order and complete chaos. The model is applied to the measured distribution of transition strength of decay-out gamma-ray lines in 194Hg, and it is found that the normally deformed states should be closer to the chaotic than the ordered situation, with GOE-type spectral correlations extending over at least 10 levels. ©2004 American Institute of Physics
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