| 1. |
- Abgrall, N., et al.
(författare)
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The large enriched germanium experiment for neutrinoless double beta decay (LEGEND)
- 2017
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Ingår i: AIP Conference Proceedings. - : Author(s). - 1551-7616 .- 0094-243X. ; 1894
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Konferensbidrag (refereegranskat)abstract
- The observation of neutrinoless double-beta decay (0νββ) would show that lepton number is violated, reveal that neu-trinos are Majorana particles, and provide information on neutrino mass. A discovery-capable experiment covering the inverted ordering region, with effective Majorana neutrino masses of 15 - 50 meV, will require a tonne-scale experiment with excellent energy resolution and extremely low backgrounds, at the level of ∼0.1 count /(FWHM·t·yr) in the region of the signal. The current generation 76Ge experiments GERDA and the Majorana Demonstrator, utilizing high purity Germanium detectors with an intrinsic energy resolution of 0.12%, have achieved the lowest backgrounds by over an order of magnitude in the 0νββ signal region of all 0νββ experiments. Building on this success, the LEGEND collaboration has been formed to pursue a tonne-scale 76Ge experiment. The collaboration aims to develop a phased 0νββ experimental program with discovery potential at a half-life approaching or at 1028 years, using existing resources as appropriate to expedite physics results.
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| 2. |
- Henning, G., et al.
(författare)
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Exploring the stability of super heavy elements: First measurement of the fission barrier of 254No
- 2014
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. ; 66
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Konferensbidrag (refereegranskat)abstract
- The gamma-ray multiplicity and total energy emitted by the heavy nucleus 254No have been measured at 2 different beam energies. From these measurements, the initial distributions of spin I and excitation energy E * of 254No were constructed. The distributions display a saturation in excitation energy, which allows a direct determination of the fission barrier. 254No is the heaviest shell-stabilized nucleus with a measured fission barrier. © Owned by the authors, published by EDP Sciences, 2014.
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| 3. |
- 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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| 4. |
- 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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| 5. |
- Henning, G., et al.
(författare)
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Fission Barrier of Superheavy Nuclei and Persistence of Shell Effects at High Spin: Cases of No-254 and Th-220
- 2014
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 113:26
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Tidskriftsartikel (refereegranskat)abstract
- We report on the first measurement of the fission barrier height in a heavy shell-stabilized nucleus. The fission barrier height of No-254 is measured to be B-f = 6.0 +/- 0.5 MeV at spin 15 (h) over bar and, by extrapolation, B-f = 6.6 +/- 0.9 MeV at spin 0 (h) over bar. This information is deduced from the measured distribution of entry points in the excitation energy versus spin plane. The same measurement is performed for Th-220 and only a lower limit of the fission barrier height can be determined: B-f (I) > 8 MeV. Comparisons with theoretical fission barriers test theories that predict properties of superheavy elements.
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| 6. |
- Lopez-Martens, A., et al.
(författare)
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Stability and synthesis of superheavy elements: Fighting the battle against fission - example of No-254
- 2016
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. - 9782759890118 ; 131
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Konferensbidrag (refereegranskat)abstract
- Superheavy nuclei exist solely due to quantum shell effects, which create a pocket in the potential-energy surface of the nucleus, thus providing a barrier against spontaneous fission. Determining the height of the fission barrier and its angular-momentum dependence is important to quantify the role that microscopic shell corrections play in enhancing and extending the limits of nuclear stability. In this talk, the first measurement of a fission barrier in the very heavy nucleus No-254 will be presented.
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| 7. |
- 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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| 8. |
- Riley, M A, et al.
(författare)
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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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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.
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| 9. |
- Hartley, D. J., et al.
(författare)
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Persistence of collective behavior at high spin in the N=88 nucleus Tb-153
- 2015
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 91:5
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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.
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| 10. |
- Al-Khatib, A, et al.
(författare)
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Transition to non-collective states at high spin in Xe-124
- 2008
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Ingår i: European Physical Journal A. Hadrons and Nuclei. - : Springer Science and Business Media LLC. - 1434-6001. ; 36:1, s. 21-29
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Tidskriftsartikel (refereegranskat)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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