| 1. |
- Akkoyun, S., et al.
(författare)
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AGATA - Advanced GAmma Tracking Array
- 2012
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Ingår i: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002 .- 0167-5087 .- 1872-9576. ; 668, s. 26-58
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Tidskriftsartikel (refereegranskat)abstract
- The Advanced GAmma Tracking Array (AGATA) is a European project to develop and operate the next generation γ-ray spectrometer. AGATA is based on the technique of γ-ray energy tracking in electrically segmented high-purity germanium crystals. This technique requires the accurate determination of the energy, time and position of every interaction as a γ ray deposits its energy within the detector volume. Reconstruction of the full interaction path results in a detector with very high efficiency and excellent spectral response. The realisation of γ-ray tracking and AGATA is a result of many technical advances. These include the development of encapsulated highly segmented germanium detectors assembled in a triple cluster detector cryostat, an electronics system with fast digital sampling and a data acquisition system to process the data at a high rate. The full characterisation of the crystals was measured and compared with detector- response simulations. This enabled pulse-shape analysis algorithms, to extract energy, time and position, to be employed. In addition, tracking algorithms for event reconstruction were developed. The first phase of AGATA is now complete and operational in its first physics campaign. In the future AGATA will be moved between laboratories in Europe and operated in a series of campaigns to take advantage of the different beams and facilities available to maximise its science output. The paper reviews all the achievements made in the AGATA project including all the necessary infrastructure to operate and support the spectrometer. © 2011 Elsevier B.V. All rights reserved.
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| 2. |
- Gottardo, A., et al.
(författare)
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New Isomers in the Neutron-Rich Region Beyond 208Pb
- 2014
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. - 9782759811755 - 9782759811762 ; 66, s. 02043-02043
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Konferensbidrag (refereegranskat)abstract
- The region of neutron-rich nuclei beyond 208Pb has been very difficult to explore due to its high mass and exoticity. However, recent experimental improvements allowed one to perform a quite extended isomer decay spectroscopy of these nuclei.
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| 3. |
- Gottardo, A., et al.
(författare)
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New μs Isomers in the Neutron-rich 210Hg Nucleus
- 2013
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 725:4-5, s. 292-296
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Tidskriftsartikel (refereegranskat)abstract
- Neutron-rich nuclei in the lead region, beyond N = 126, have been studied at the FRS-RISING setup at GSI, exploiting the fragmentation of a primary uranium beam. Two isomeric states have been identified in Hg-210: the 8(+) isomer expected from the seniority scheme in the vg(9/2) shell and a second one at low spin and low excitation energy. The decay strength of the 8(+) isomer confirms the need of effective three-body forces in the case of neutron-rich lead isotopes. The other unexpected low-lying isomer has been tentatively assigned as a 3(-) state, although this is in contrast with theoretical expectations. (C) 2013 Elsevier B.V. All rights reserved.
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| 4. |
- Benzoni, G., et al.
(författare)
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First Measurement of Beta Decay Half-lives in Neutron-rich Tl and Bi Isotopes
- 2012
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 715:4-5, s. 293-297
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Tidskriftsartikel (refereegranskat)abstract
- Neutron-rich isotopes around lead, beyond N = 126, have been studied exploiting the fragmentation of an uranium primary beam at the FRS-RISING setup at GSI. For the first time beta-decay half-lives of Bi-219 and Tl-211,Tl-212,Tl-213 isotopes have been derived. The half-lives have been extracted using a numerical simulation developed for experiments in high-background conditions. Comparison with state of the art models used in r-process calculations is given, showing a systematic underestimation of the experimental values, at variance from close-lying nuclei. (c) 2012 Elsevier B.V. All rights reserved.
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| 5. |
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| 6. |
- Besga, A., et al.
(författare)
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Differences in brain cholesterol metabolism and insulin in two subgroups of patients with different CSF biomarkers but similar white matter lesions suggest different pathogenic mechanisms
- 2012
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Ingår i: Neuroscience Letters. - : Elsevier BV. - 0304-3940 .- 1872-7972. ; 510:2, s. 121-126
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Tidskriftsartikel (refereegranskat)abstract
- Investigate possible associations of white matter hyperintensities (WMHs) with the metabolism of cholesterol and insulin in two subgroups of patients with memory complaints and different CSF A beta 42 and CSF tau levels. 59 patients from the memory clinic at Karolinska Hospital were included. Degree of WMHs was rated using the ARWMC scale and the following biomarkers were measured in CSF and plasma: insulin, cholesterol, lanosterol, lathosterol, and oxidized cholesterol metabolites. The WMHs in CSF control-like group correlated with increased brain cholesterol synthesis and reduced efflux of oxysterols and insulin in CSF. In the CSF AD-like group, the WMHs correlated with increased peripheral cholesterol metabolism. Despite having similar appearance on FLAIR images, the pathogenic mechanisms of WMHS are likely to be different in the two groups investigated.
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| 7. |
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| 8. |
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| 9. |
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| 10. |
- Crespi, F. C. L., et al.
(författare)
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Isospin Character of Low-Lying Pygmy Dipole States in Pb-208 via Inelastic Scattering of O-17 Ions
- 2014
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 113:1, s. 012501-
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Tidskriftsartikel (refereegranskat)abstract
- The properties of pygmy dipole states in Pb-208 were investigated using the Pb-208(O-17, O-17'gamma) reaction at 340 MeV and measuring the gamma decay with high resolution with the AGATA demonstrator array. Cross sections and angular distributions of the emitted gamma rays and of the scattered particles were measured. The results are compared with (gamma, gamma') and (p, p') data. The data analysis with the distorted wave Born approximation approach gives a good description of the elastic scattering and of the inelastic excitation of the 2(+) and 3(-) states. For the dipole transitions a form factor obtained by folding a microscopically calculated transition density was used for the first time. This has allowed us to extract the isoscalar component of the 1(-) excited states from 4 to 8 MeV.
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| 11. |
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| 12. |
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| 13. |
- Denis Bacelar, A.M., et al.
(författare)
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The population of metastable states as a probe of relativistic-energy fragmentation reactions
- 2013
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 723:4–5, s. 302-306
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Tidskriftsartikel (refereegranskat)abstract
- Isomeric ratios have been measured for high-spin states in Po-198,200,206,208(84), At-208,209,210,211(85), Rn-210,211,212,213,214(86), Fr-208,211,212,213,214(87), Ra-210,211,212,214,215(88), and Ac-215(89) following the projectile fragmentation of a 1 AGeV U-238 beam by a Be-9 target at GSI Helmholtzzentrum fur Schwerionenforschung. The fragments were separated in the fragment separator (FRS) and identified by means of energy loss and time-of-flight techniques. They were brought to rest at the centre of the RISING gamma-ray detector array and intensities of gamma rays emitted in the decay of isomeric states with half-lives between 100 ns and 40 mu s and spin values up to 55/2 (h) over bar were used to obtain the corresponding isomeric ratios. The data are compared to theoretical isomeric ratios calculated in the framework of the abrasion-ablation model. Large experimental enhancements are obtained for high-spin isomers in comparison to expected values. (C) 2013 Elsevier B.V. All rights reserved.
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| 14. |
- Gottardo, A., et al.
(författare)
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Isomeric Decay Spectroscopy of the 217Bi Isotope
- 2014
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 90:3
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Tidskriftsartikel (refereegranskat)abstract
- The structure of the neutron-rich bismuth isotope 217Bi has been studied for the first time. The fragmentation of a primary 238U beam at the FRS-RISING setup at GSI was exploited to perform γ-decay spectroscopy, since μs isomeric states were expected in this nucleus. Gamma rays following the decay of a t1/2=3 μs isomer were observed, allowing one to establish the low-lying structure of 217Bi. The level energies and the reduced electric quadrupole transition probability B(E2) from the isomeric state are compared to large-scale shell-model calculations.
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| 15. |
- Gottardo, A., et al.
(författare)
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Isomers in Neutron-rich Lead Isotopes Populated via the Fragmentation of 238U at 1 GeV A
- 2011
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6596 .- 1742-6588. ; 312
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Tidskriftsartikel (refereegranskat)abstract
- Neutron-rich nuclei beyond N = 126 in the lead region were populated by fragmenting a 238U beam at 1 GeV A on a Be target and then separated by the Fragment Separator (FRS) at GSI. Their isomeric decays were observed, enabling study of the shell structure of neutron-rich nuclei around the Z=82 shell closure. Some preliminary results are reported in this paper.
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| 16. |
- Gottardo, A., et al.
(författare)
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New Isomers in the Full Seniority Scheme of Neutron-rich Lead Isotopes: The Role of Effective Three-body Forces
- 2012
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Ingår i: Physical Review Letters. - 1079-7114. ; 109:16
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Tidskriftsartikel (refereegranskat)abstract
- The neutron-rich lead isotopes, up to Pb-216, have been studied for the first time, exploiting the fragmentation of a primary uranium beam at the FRS-RISING setup at GSI. The observed isomeric states exhibit electromagnetic transition strengths which deviate from state-of-the-art shell-model calculations. It is shown that their complete description demands the introduction of effective three-body interactions and two-body transition operators in the conventional neutron valence space beyond Pb-208.
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| 17. |
- Hadynska-Klek, K., et al.
(författare)
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Towards The Determination Of Superdeformation In Ca-42
- 2013
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Ingår i: Acta Physica Polonica B. - 0587-4254 .- 1509-5770. ; 44:3, s. 617-625
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Tidskriftsartikel (refereegranskat)abstract
- The Coulomb excitation experiment to study electromagnetic structure of low-lying states in Ca-42 with a focus on a possible superdeformation in this nucleus was performed at the Laboratori Nazionali di Legnaro in Italy. Preliminary values of the determined quadrupole deformation parameters for both the ground state band and the presumed superdeformed band are presented.
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| 18. |
- John, P. R., et al.
(författare)
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Shape evolution in the neutron-rich osmium isotopes : Prompt gamma-ray spectroscopy of Os-196
- 2014
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Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 90:2, s. 021301-
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Tidskriftsartikel (refereegranskat)abstract
- The shape transition in the neutron-rich Os isotopes is studied by investigating the neutron-rich Os-196 nucleus through in-beam gamma-ray spectroscopy using a two-proton transfer reaction from a Pt-198 target to a Se-82 beam. The beam-like recoils were detected and identified with the large-acceptance magnetic spectrometer PRISMA, and the coincident gamma rays were measured with the advanced gamma tracking array (AGATA) demonstrator. The de-excitation of the low-lying levels of the yrast-band of Os-196 were identified for the first time. The results are compared with state-of-the-art beyond-mean-field calculations, performed for the even-even Os188-198 isotopes. The new results suggest a smooth transition in the Os isotopes from a more axial rotational behavior towards predominately vibrational nuclei through triaxial configurations. An almost perfect gamma-unstable/triaxial rotor yrast band is predicted for Os-196 which is in agreement with the experimentally measured excited states.
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| 19. |
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| 21. |
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| 22. |
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| 23. |
- Modamio, V., et al.
(författare)
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Lifetime measurements in neutron-rich Co-63,Co-65 isotopes using the AGATA demonstrator
- 2013
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Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 88:4, s. 044326-
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Tidskriftsartikel (refereegranskat)abstract
- Lifetimes of the low-lying (11/2(-)) states in Co-63,Co-65 have been measured employing the recoil distance doppler shift method (RDDS) with the AGATA gamma-ray array and the PRISMA mass spectrometer. These nuclei were populated via a multinucleon transfer reaction by bombarding a U-238 target with a beam of Ni-64. The experimental B(E2) reduced transition probabilities for Co-63,Co-65 are well reproduced by large-scale shell-model calculations that predict a constant trend of the B(E2) values up to the N = 40 Co-67 isotope.
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| 24. |
- Morales, A.I., et al.
(författare)
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β-decay Studies of Neutron-rich Tl, Pb, and Bi Isotopes
- 2014
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 89:1
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Tidskriftsartikel (refereegranskat)abstract
- The fragmentation of relativistic uranium projectiles has been exploited at the Gesellschaft für Schwerionenforschung laboratory to investigate the β decay of neutron-rich nuclei just beyond 208Pb. This paper reports on β-delayed γ decays of 211–213Tl, 215Pb, and 215–219Bi de-exciting states in the daughters 211–213Pb, 215Bi, and 215–219Po. The resulting partial level schemes, proposed with the help of systematics and shell-model calculations, are presented. The role of allowed Gamow-Teller and first-forbidden β transitions in this mass region is discussed.
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| 25. |
- Pellegri, L., et al.
(författare)
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Pygmy dipole resonance in Sn-124 populated by inelastic scattering of O-17
- 2014
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 738, s. 519-523
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Tidskriftsartikel (refereegranskat)abstract
- The gamma decay from the high-lying states of Sn-124 was measured using the inelastic scattering of O-17 at 340 MeV. The emitted gamma rays were detected with high resolution with the AGATA demonstrator array and the scattered ions were detected in two segmented Delta E-E silicon telescopes. The angular distribution was measured both for the gamma rays and the scattered O-17 ions. An accumulation of E1 strength below the particle threshold was found and compared with previous data obtained with (gamma,gamma') and (alpha,alpha'gamma) reactions. The present results of elastic scattering, and excitation of E2 and E1 states were analysed using the DWBA approach. From this comprehensive description the isoscalar component of the 1-excited states was extracted. The obtained values are based on the comparison of the data with DWBA calculations including a form factor deduced using a microscopic transition density.
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| 26. |
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| 27. |
- Vandone, V., et al.
(författare)
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Global properties of K hindrance probed by the gamma decay of the warm rotating W-174 nucleus
- 2013
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Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 88:3, s. 034312-
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Tidskriftsartikel (refereegranskat)abstract
- The K hindrance to the gamma decay is studied in the warm rotating W-174 nucleus, focusing on the weakening of the selection rules of the K quantum number with increasing excitation energy. W-174 was populated by the fusion reaction of Ti-50 (at 217 MeV) on a Te-128 target, and its gamma decay was detected by the AGATA Demonstrator array coupled to a BaF2 multiplicity filter at Laboratori Nazionali di Legnaro of INFN. A fluctuation analysis of gamma coincidence matrices gives a similar number of low-K and high-K discrete excited bands. The results are compared to simulations of the gamma-decay flow based on a microscopic cranked shell model at finite temperature in which the K mixing is governed by the interplay of Coriolis force with the residual interaction. Agreement between simulations and experiment is obtained only by hindering the E1 decay between low-K and high-K bands by an amount compatible with that determined by spectroscopic studies of K isomers in the same mass region, with a similar trend with excitation energy. The work indicates that K mixing due to temperature effects may play a leading role for the entire body of discrete excited bands, which probes the onset region of K weakening.
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| 28. |
- Vandone, V, et al.
(författare)
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Study of the Order-to-Chaos transition in 174 W with the AGATA-Demonstrator
- 2012
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Ingår i: Journal of Physics: Conference Series. ; 366:1
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Tidskriftsartikel (refereegranskat)abstract
- The transition between order and chaos is studied in the warm rotating nucleus 174 W by γ-spectroscopy, focusing on the conservation of selection rules of the K quantum number with the excitation energy, where K is the projection of the total angular momentum on the symmetry axis. The 174 W nucleus was populated by the fusion-evaporation reaction of 80 Ti (at 217 MeV) on a 128 Te backed target. The measurement was performed in July 2010 at Legnaro National Laboratories of INFN using the AGATA Demonstrator HPGe-array coupled to an array of 27 BaF 2 scintillators, named Helena. The data analysis concentrates on γ-γ coincidence matrices selecting the γ-decay flow populating low- K and high- K structures. By a statistical fluctuation analysis the total number of low- K and high- K bands can be evaluated as a function of excitation energy. Comparisons with cranked shell model calculations at finite temperature are used to extract information on the onset of the chaotic regime as a function of excitation energy.
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