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| 2. |
- Reifarth, R., et al.
(författare)
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Nuclear astrophysics with radioactive ions at FAIR
- 2016
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 665:1
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Konferensbidrag (refereegranskat)abstract
- The nucleosynthesis of elements beyond iron is dominated by neutron captures in the s and r processes. However, 32 stable, proton-rich isotopes cannot be formed during those processes, because they are shielded from the s-process flow and r-process beta-decay chains. These nuclei are attributed to the p and rp process. For all those processes, current research in nuclear astrophysics addresses the need for more precise reaction data involving radioactive isotopes. Depending on the particular reaction, direct or inverse kinematics, forward or time-reversed direction are investigated to determine or at least to constrain the desired reaction cross sections. The Facility for Antiproton and Ion Research (FAIR) will offer unique, unprecedented opportunities to investigate many of the important reactions. The high yield of radioactive isotopes, even far away from the valley of stability, allows the investigation of isotopes involved in processes as exotic as the r or rp processes.
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| 3. |
- Tarrío, Diego, et al.
(författare)
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Measurement of the angular distribution of fission fragments using a PPAC assembly at CERN n_TOF
- 2014
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 743, s. 79-85
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Tidskriftsartikel (refereegranskat)abstract
- A fission reaction chamber based on Parallel Plate Avalanche Counters (PPACs) was built for measuring angular distributions of fragments emitted in neutron-induced fission of actinides at the neutron beam available at the Neutron Time-Of-Flight (n_TOF) facility at CERN. The detectors and the samples were tilted 45 degrees with respect to the neutron beam direction to cover all the possible values of the emission angle of the fission fragments. The main features of this setup are discussed and results on the fission fragment angular distribution are provided for the Th-232(n,f) reaction around the fission threshold. The results are compared with the available data in the literature, demonstrating the good capabilities of this setup.
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| 4. |
- Tarrío, Diego, et al.
(författare)
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Neutron-induced fission cross sections of Th-232 and U-233 up to 1 GeV using parallel plate avalanche counters at the CERN n_TOF facility
- 2023
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Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 107:4
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Tidskriftsartikel (refereegranskat)abstract
- The neutron-induced fission cross sections of Th-232 and U-233 were measured relative to U-235 in a wide neutron energy range up to 1 GeV (and from fission threshold in the case of Th-232, and from 0.7 eV in case of U-233), using the white-spectrum neutron source at the CERN Neutron Time-of-Flight (n_TOF) facility. Parallel plate avalanche counters (PPACs) were used, installed at the Experimental Area 1 (EAR1), which is located at 185 m from the neutron spallation target. The anisotropic emission of fission fragments were taken into account in the detection efficiency by using, in the case of U-233, previous results available in EXFOR, whereas in the case of Th-232 these data were obtained from our measurement, using PPACs and targets tilted 45 degrees with respect to the neutron beam direction. Finally, the obtained results are compared with past measurements and major evaluated nuclear data libraries. Calculations using the high-energy reaction models INCL++ and ABLA07 were performed and some of their parameters were modified to reproduce the experimental results. At high energies, where no other neutron data exist, our results are compared with experimental data on proton-induced fission. Moreover, the dependence of the fission cross section at 1 GeV with the fissility parameter of the target nucleus is studied by combining those ( p, f) data with our (n, f) data on Th-232 and U-233 and on other isotopes studied earlier at n_TOF using the same experimental setup.
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| 5. |
- Altstadt, S.G., et al.
(författare)
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B-13,B-14(n,gamma) via Coulomb Dissociation for Nucleosynthesis towards the r-Process
- 2014
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Ingår i: Nuclear Data Sheets. - : Elsevier BV. - 1095-9904 .- 0090-3752. ; 120, s. 197-200
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Konferensbidrag (refereegranskat)abstract
- Radioactive beams of 14,15B produced by fragmentation of a primary 40Ar beam were directed onto a Pb target to investigate the neutron breakup within the Coulomb field. The experiment was performed at the LAND/R3B setup. Preliminary results for the Coulomb dissociation cross sections as well as for the astrophysically interesting inverse reactions, 13,14B(n,γ), are presented.
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| 6. |
- Atar, L., et al.
(författare)
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Quasifree (p, 2p) Reactions on Oxygen Isotopes: Observation of Isospin Independence of the Reduced Single-Particle Strength
- 2018
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 120:5
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Tidskriftsartikel (refereegranskat)abstract
- Quasifree one-proton knockout reactions have been employed in inverse kinematics for a systematic study of the structure of stable and exotic oxygen isotopes at the R3B/LAND setup with incident beam energies in the range of 300-450 MeV/u. The oxygen isotopic chain offers a large variation of separation energies that allows for a quantitative understanding of single-particle strength with changing isospin asymmetry. Quasifree knockout reactions provide a complementary approach to intermediate-energy one-nucleon removal reactions. Inclusive cross sections for quasifree knockout reactions of the type OA(p,2p)NA-1 have been determined and compared to calculations based on the eikonal reaction theory. The reduction factors for the single-particle strength with respect to the independent-particle model were obtained and compared to state-of-the-art ab initio predictions. The results do not show any significant dependence on proton-neutron asymmetry.
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| 7. |
- Boillos, J. M., et al.
(författare)
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Isotopic cross sections of fragmentation residues produced by light projectiles on carbon near
- 2022
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Ingår i: Physical Review C. - 2469-9993 .- 2469-9985. ; 105:1
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Tidskriftsartikel (refereegranskat)abstract
- We measured 135 cross sections of residual nuclei produced in fragmentation reactions of C12, N14, and O13−16,20,22 projectiles impinging on a carbon target at kinetic energies of near 400A MeV, most of them for the first time, with the RB3/LAND setup at the GSI facility in Darmstadt (Germany). The use of this state-of-the-art experimental setup in combination with the inverse kinematics technique gave the full identification in atomic and mass numbers of fragmentation residues with a high precision. The cross sections of these residues were determined with uncertainties below 20% for most of the cases. These data are compared to other previous measurements with stable isotopes and are also used to benchmark different model calculations.
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| 8. |
- Caesar, C., et al.
(författare)
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Beyond the neutron drip line: The unbound oxygen isotopes O-25 and O-26
- 2013
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Ingår i: Physical Review C - Nuclear Physics. - 2469-9985 .- 2469-9993 .- 0556-2813. ; 88:3
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Tidskriftsartikel (refereegranskat)abstract
- The very neutron-rich oxygen isotopes O-25 and O-26 are investigated experimentally and theoretically. The unbound states are populated in an experiment performed at the R3B-LAND setup at GSI via proton-knockout reactions from F-26 and F-27 at relativistic energies around 442 and 414 MeV/nucleon, respectively. From the kinematically complete measurement of the decay into O-24 plus one or two neutrons, the O-25 ground-state energy and width are determined, and upper limits for the O-26 ground-state energy and lifetime are extracted. In addition, the results provide indications for an excited state in O-26 at around 4 MeV. The experimental findings are compared to theoretical shell-model calculations based on chiral two- and three-nucleon (3N) forces, including for the first time residual 3N forces, which are shown to be amplified as valence neutrons are added.
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| 9. |
- Heine, M., et al.
(författare)
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Determination of the neutron-capture rate of C-17 for r-process nucleosynthesis
- 2017
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Ingår i: Physical Review C. - 2469-9985 .- 2469-9993. ; 95:1, s. Article no 014613 -
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Tidskriftsartikel (refereegranskat)abstract
- With the (RB)-B-3-LAND setup at GSI we have measured exclusive relative-energy spectra of the Coulomb dissociation of C-18 at a projectile energy around 425A MeV on a lead target, which are needed to determine the radiative neutron-capture cross sections of C-17 into the ground state of C-18. Those data have been used to constrain theoretical calculations for transitions populating excited states in C-18. This allowed to derive the astrophysical cross section sigma(n gamma)*. accounting for the thermal population of C-17 target states in astrophysical scenarios. The experimentally verified capture rate is significantly lower than those of previously obtained Hauser-Feshbach estimations at temperatures T-9
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| 10. |
- Ribeiro, G., et al.
(författare)
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Structure of Be-13 studied in proton knockout from B-14
- 2018
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Ingår i: Physical Review C. - 2469-9985 .- 2469-9993. ; 98:2
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Tidskriftsartikel (refereegranskat)abstract
- The neutron-unbound isotope Be-13 has been studied in several experiments using different reactions, different projectile energies, and different experimental setups. There is, however, no real consensus in the interpretation of the data, in particular concerning the structure of the low-lying excited states. Gathering new experimental information, which may reveal the Be-13 structure, is a challenge, particularly in light of its bridging role between Be-12, where the N = 8 neutron shell breaks down, and the Borromean halo nucleus Be-14. The purpose of the present study is to investigate the role of bound excited states in the reaction product Be-12 after proton knockout from B-14, by measuring coincidences between Be-12, neutrons, and gamma rays originating from de-excitation of states fed by neutron decay of Be-13. The Be-13 isotopes were produced in proton knockout from a 400 MeV/nucleon B-14 beam impinging on a CH2 target. The Be-12-n relative-energy spectrum d sigma/dE(fn) was obtained from coincidences between Be-12(g.s.) and a neutron, and also as threefold coincidences by adding gamma rays, from the de-excitation of excited states in Be-12. Neutron decay from the first 5/2(+) state in Be-13 to the 2(+) state in Be-12 at 2.11 MeV is confirmed. An energy independence of the proton-knockout mechanism is found from a comparison with data taken with a 35 MeV/nucleon B-14 beam. A low-lying p-wave resonance in Be-13(1/2(-)) is confirmed by comparing proton- and neutron-knockout data from B-14 and Be-14.
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