| 1. |
- Barzakh, A., et al.
(author)
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Large Shape Staggering in Neutron-Deficient Bi Isotopes
- 2021
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In: Physical Review Letters. - 0031-9007. ; 127:19
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Journal article (peer-reviewed)abstract
- The changes in the mean-square charge radius (relative to Bi209), magnetic dipole, and electric quadrupole moments of Bi187,188,189,191 were measured using the in-source resonance-ionization spectroscopy technique at ISOLDE (CERN). A large staggering in radii was found in Bi187,188,189g, manifested by a sharp radius increase for the ground state of Bi188 relative to the neighboring Bi187,189g. A large isomer shift was also observed for Bi188m. Both effects happen at the same neutron number, N=105, where the shape staggering and a similar isomer shift were observed in the mercury isotopes. Experimental results are reproduced by mean-field calculations where the ground or isomeric states were identified by the blocked quasiparticle configuration compatible with the observed spin, parity, and magnetic moment. © 2021 authors.
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| 2. |
- Andel, B., et al.
(author)
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β -delayed fission of isomers in Bi 188
- 2020
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In: Physical Review C. - 2469-9985. ; 102:1
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Journal article (peer-reviewed)abstract
- β-delayed fission (βDF) decay of a low-spin (ls) and a high-spin (hs) isomer in Bi188 was studied at the ISOLDE facility at CERN. Isomer-selective laser ionization and time gating were employed to investigate each isomer separately and their βDF partial half-lives were determined: T1/2p,βDF(188Bihs)=5.6(8)×103 s and T1/2p,βDF(188Bils)=1.7(6)×103 s. This work is the first βDF study of two states in one isotope and allows the spin dependence of low-energy fission to be explored. The fission fragment mass distribution of a daughter nuclide Pb188, following the β decay of the high-spin isomer, was deduced and indicates a mixture of symmetric and asymmetric fission modes. Experimental results were compared with self-consistent mean-field calculations based on the finite-range Gogny D1M interaction. To reproduce the measured T1/2p,βDF(188Bihs), the calculated fission barrier of Pb188 had to be reduced by ≈30%. After this reduction, the measured T1/2p,βDF(188Bils) was in agreement with calculations for a few possible configurations for Bils188. Theoretical βDF probabilities for these configurations were found to be lower by a factor of 4-9 than the βDF probability of Bihs188. The fission fragment mass distribution of Pb188 was compared to the scission-point model SPY and the calculations based on the finite-range liquid-drop model. The first observation of βDF for Bi190 is also reported. © 2020 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
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| 3. |
- Orejas, C, et al.
(author)
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Cold-water corals in aquaria: advances and challenges. A focus on the Mediterranean
- 2019
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In: Mediterranean Cold-Water Corals: Past, Present and Future. - : Springer. - 2213-719X. - 9783319916071
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Book chapter (peer-reviewed)abstract
- Knowledge on basic biological functions of organisms is essential to understand not only the role they play in the ecosystems but also to manage and protect their populations. The study of biological processes, such as growth, reproduction and physiology, which can be approached in situ or by collecting exemplars and rearing them in aquaria, is particularly challenging for deep-sea organisms such as cold-water corals (CWCs). Present experimental work and monitoring of deep-sea populations is still a chimera. Only a handful of research institutes or companies have been able to install in situ marine observatories in the Mediterranean Sea or elsewhere, which facilitate for a continuous monitoring of deep-sea ecosystems. Hence, today’s best way to obtain basic biological information on these organisms is (1) working with collected samples and analysing them post-mortem and / or (2) cultivating corals in aquaria in order to monitor biological processes and investigate coral behaviour and physiological responses under different experimental treatments. The first challenging aspect is the collection process, which implies the use of oceanographic research vessels in most occasions, since these organisms inhabit areas between ca. 150 m to more than 1,000 m depth, and specific sampling gears. The next challenge is the maintenance of the animals on board (in situations where cruises may take weeks) and their transport to home laboratories. Maintenance in the home labs is also extremely challenging since special conditions and set ups are needed to conduct experimental studies to obtain information on the biological processes of these animals. The complexity of the natural environment from which the corals were collected cannot be exactly replicated within the laboratory setting; a fact which has led some researchers to question the validity of work and conclusions drawn from such undertakings. It is evident that aquaria experiments cannot perfectly reflect the real environmental and trophic conditions where these organisms occur, but: (1) in most cases we do not have the possibility to obtain equivalent in situ information and (2) even with limitations, they produce relevant information about 117 the biological limits of the species, which is especially valuable when considering potential future climate change scenarios. This chapter includes many contributions from different authors and it intends to be both, a practical “handbook” for conducting CWC aquaria work, while at the same time, to offer an overview on the CWC research conducted in Mediterranean labs equipped with aquaria infrastructure. Experiences from Atlantic and Pacific laboratories with extensive experience with CWC work have also contributed to this chapter, as their procedures are valuable to any researcher interested in conducting experimental work with CWC in aquaria. It was impossible to include contributions from all labs in the world currently working experimentally with CWCs in the laboratory, but at the conclusion of the chapter we attempt, to our best of our knowledge, to supply a list of laboratories with operational CWC aquaria facilities.
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| 4. |
- Clément, E., et al.
(author)
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Low-energy Coulomb excitation of Sr 96,98 beams
- 2016
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In: Physical Review C - Nuclear Physics. - 0556-2813. ; 94:5, s. 054326-
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Journal article (peer-reviewed)abstract
- The structure of neutron-rich Sr96,98 nuclei was investigated by low-energy safe Coulomb excitation of radioactive beams at the REX-ISOLDE facility, CERN, with the MINIBALL spectrometer. A rich set of transitional and diagonal E2 matrix elements, including those for non-yrast structures, has been extracted from the differential Coulomb-excitation cross sections. The results support the scenario of a shape transition at N=60, giving rise to the coexistence of a highly deformed prolate and a spherical configuration in Sr98, and are compared to predictions from several theoretical calculations. The experimental data suggest a significant contribution of the triaxal degree of freedom in the ground state of both isotopes. In addition, experimental information on low-lying states in Rb98 has been obtained.
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| 5. |
- Clément, E, et al.
(author)
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Spectroscopic Quadrupole Moments in ^{96,98}Sr: Evidence for Shape Coexistence in Neutron-Rich Strontium Isotopes at N=60.
- 2016
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In: Physical Review Letters. - 1079-7114. ; 116:2
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Journal article (peer-reviewed)abstract
- Neutron-rich ^{96,98}Sr isotopes have been investigated by safe Coulomb excitation of radioactive beams at the REX-ISOLDE facility. Reduced transition probabilities and spectroscopic quadrupole moments have been extracted from the differential Coulomb excitation cross sections. These results allow, for the first time, the drawing of definite conclusions about the shape coexistence of highly deformed prolate and spherical configurations. In particular, a very small mixing between the coexisting states is observed, contrary to other mass regions where strong mixing is present. Experimental results have been compared to beyond-mean-field calculations using the Gogny D1S interaction in a five-dimensional collective Hamiltonian formalism, which reproduce the shape change at N=60.
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