| 1. |
- Aad, G., et al.
(författare)
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- 2010
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swepub:Mat__t
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| 2. |
- Aad, G., et al.
(författare)
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- 2011
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swepub:Mat__t
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| 3. |
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| 4. |
- Aad, G., et al.
(författare)
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- 2010
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swepub:Mat__t
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| 5. |
- Aad, G., et al.
(författare)
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- 2010
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swepub:Mat__t
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| 6. |
- Aad, G., et al.
(författare)
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- 2010
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swepub:Mat__t
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| 7. |
- Abel, I, et al.
(författare)
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Overview of the JET results with the ITER-like wall
- 2013
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 53:10, s. 104002-
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Tidskriftsartikel (refereegranskat)abstract
- Following the completion in May 2011 of the shutdown for the installation of the beryllium wall and the tungsten divertor, the first set of JET campaigns have addressed the investigation of the retention properties and the development of operational scenarios with the new plasma-facing materials. The large reduction in the carbon content (more than a factor ten) led to a much lower Z(eff) (1.2-1.4) during L- and H-mode plasmas, and radiation during the burn-through phase of the plasma initiation with the consequence that breakdown failures are almost absent. Gas balance experiments have shown that the fuel retention rate with the new wall is substantially reduced with respect to the C wall. The re-establishment of the baseline H-mode and hybrid scenarios compatible with the new wall has required an optimization of the control of metallic impurity sources and heat loads. Stable type-I ELMy H-mode regimes with H-98,H-y2 close to 1 and beta(N) similar to 1.6 have been achieved using gas injection. ELM frequency is a key factor for the control of the metallic impurity accumulation. Pedestal temperatures tend to be lower with the new wall, leading to reduced confinement, but nitrogen seeding restores high pedestal temperatures and confinement. Compared with the carbon wall, major disruptions with the new wall show a lower radiated power and a slower current quench. The higher heat loads on Be wall plasma-facing components due to lower radiation made the routine use of massive gas injection for disruption mitigation essential.
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| 8. |
- Romanelli, F, et al.
(författare)
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Overview of the JET results
- 2011
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 51:9
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Tidskriftsartikel (refereegranskat)abstract
- Since the last IAEA Conference JET has been in operation for one year with a programmatic focus on the qualification of ITER operating scenarios, the consolidation of ITER design choices and preparation for plasma operation with the ITER-like wall presently being installed in JET. Good progress has been achieved, including stationary ELMy H-mode operation at 4.5 MA. The high confinement hybrid scenario has been extended to high triangularity, lower ρ*and to pulse lengths comparable to the resistive time. The steady-state scenario has also been extended to lower ρ*and ν*and optimized to simultaneously achieve, under stationary conditions, ITER-like values of all other relevant normalized parameters. A dedicated helium campaign has allowed key aspects of plasma control and H-mode operation for the ITER non-activated phase to be evaluated. Effective sawtooth control by fast ions has been demonstrated with3He minority ICRH, a scenario with negligible minority current drive. Edge localized mode (ELM) control studies using external n = 1 and n = 2 perturbation fields have found a resonance effect in ELM frequency for specific q95values. Complete ELM suppression has, however, not been observed, even with an edge Chirikov parameter larger than 1. Pellet ELM pacing has been demonstrated and the minimum pellet size needed to trigger an ELM has been estimated. For both natural and mitigated ELMs a broadening of the divertor ELM-wetted area with increasing ELM size has been found. In disruption studies with massive gas injection up to 50% of the thermal energy could be radiated before, and 20% during, the thermal quench. Halo currents could be reduced by 60% and, using argon/deuterium and neon/deuterium gas mixtures, runaway electron generation could be avoided. Most objectives of the ITER-like ICRH antenna have been demonstrated; matching with closely packed straps, ELM resilience, scattering matrix arc detection and operation at high power density (6.2 MW m-2) and antenna strap voltages (42 kV). Coupling measurements are in very good agreement with TOPICA modelling. © 2011 IAEA, Vienna.
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| 9. |
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Overview of the JET results
- 2015
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 55:10
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Tidskriftsartikel (refereegranskat)
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| 10. |
- 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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| 11. |
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| 12. |
- 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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| 13. |
- 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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| 14. |
- Thies, Ronja, 1987, et al.
(författare)
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Systematic investigation of projectile fragmentation using beams of unstable B and C isotopes
- 2016
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Ingår i: Physical Review C - Nuclear Physics. - 2469-9985 .- 2469-9993 .- 0556-2813. ; 93:5
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Tidskriftsartikel (refereegranskat)abstract
- Models describing nuclear fragmentation and fragmentation fission deliver important input for planning nuclear physics experiments and future radioactive ion beam facilities. These models are usually benchmarked against data from stable beam experiments. In the future, two-step fragmentation reactions with exotic nuclei as stepping stones are a promising tool for reaching the most neutron-rich nuclei, creating a need for models to describe also these reactions. Purpose: We want to extend the presently available data on fragmentation reactions towards the light exotic region on the nuclear chart. Furthermore, we want to improve the understanding of projectile fragmentation especially for unstable isotopes. Method: We have measured projectile fragments from C10,12-18 and B10-15 isotopes colliding with a carbon target. These measurements were all performed within one experiment, which gives rise to a very consistent data set. We compare our data to model calculations. Results: One-proton removal cross sections with different final neutron numbers (1pxn) for relativistic C10,12-18 and B10-15 isotopes impinging on a carbon target. Comparing model calculations to the data, we find that the epax code is not able to describe the data satisfactorily. Using abrabla07 on the other hand, we find that the average excitation energy per abraded nucleon needs to be decreased from 27 MeV to 8.1 MeV. With that decrease abrabla07 describes the data surprisingly well. Conclusions: Extending the available data towards light unstable nuclei with a consistent set of new data has allowed a systematic investigation of the role of the excitation energy induced in projectile fragmentation. Most striking is the apparent mass dependence of the average excitation energy per abraded nucleon. Nevertheless, this parameter, which has been related to final-state interactions, requires further study.
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| 15. |
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| 16. |
- Browne, F., et al.
(författare)
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Pairing Forces Govern Population of Doubly Magic Ca-54 from Direct Reactions
- 2021
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Ingår i: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 126:25
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Tidskriftsartikel (refereegranskat)abstract
- Direct proton-knockout reactions of Sc-55 at similar to 220 MeV/nucleon were studied at the RIKEN Radioactive Isotope Beam Factory. Populated states of Ca-54 were investigated through -ray and invariant-mass spectroscopy. Level energies were calculated from the nuclear shell model employing a phenomenological intemucleon interaction. Theoretical cross sections to states were calculated from distorted-wave impulse approximation estimates multiplied by the shell model spectroscopic factors, which describe the wave function overlap of the Sc-55 ground state with states in Ca-54. Despite the calculations showing a significant amplitude of excited neutron configurations in the ground-state of Sc-55, valence proton removals populated predominantly the ground state of Ca-54. This counterintuitive result is attributed to pairing effects leading to a dominance of the ground-state spectroscopic factor. Owing to the ubiquity of the pairing interaction, this argument should be generally applicable to direct knockout reactions from odd-even to even-even nuclei.
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| 17. |
- 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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| 18. |
- Chakraborty, S., et al.
(författare)
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Ground-state configuration of neutron-rich Aluminum isotopes through Coulomb breakup
- 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
- Neutron-rich 34,35Al isotopes have been studied through Coulomb excitation using LAND-FRS setup at GSI, Darmstadt. The method of invariant mass analysis has been used to reconstruct the excitation energy of the nucleus prior to decay. Comparison of experimental CD cross-section with direct breakup model calculation with neutron in p3/2 orbital favours 34Al(g.s) - νp3/2 as ground state configuration of 35Al. But ground state configuration of 34Al is complicated as evident from γ-ray spectra of 33Al after Coulomb breakup of 34Al. © Owned by the authors, published by EDP Sciences, 2014.
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| 19. |
- Rahaman, A., et al.
(författare)
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Study of ground state wave-function of the Neutron-rich 29,30Na isotopes through coulomb breakup
- 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
- Coulomb breakup of unstable neutron rich nuclei 29,30Na around the 'island of inversion' has been studied at energy around 434 MeV/nucleon and 409 MeV/nucleon respectively. Four momentum vectors of fragments, decay neutron from excited projectile and γ-rays emitted from excited fragments after Coulomb breakup are measured in coincidence. For these nuclei, the low-lying dipole strength above one neutron threshold can be explained by direct breakup model. The analysis for Coulomb breakup of 29,30Na shows that large amount of the cross section yields the 28Na, 29Na core in ground state. The predominant ground-state configuration of 29,30Na is found to be 28Na(g.s) νs1/2 and 29Na(g.s) νs1/2,respectively. © Owned by the authors, published by EDP Sciences, 2014.
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| 20. |
- Wamers, F., et al.
(författare)
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Exclusive measurements of nuclear breakup reactions of 17Ne
- 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
- We have studied one-proton-removal reactions of about 500MeV/u 17Ne beams on a carbon target at the R3B/LAND setup at GSI by detecting beam-like 15O-p and determining their relative-energy distribution. We exclusively selected the removal of a 17Ne halo proton, and the Glauber-model analysis of the 16F momentum distribution resulted in an s2 contribution in the 17Ne ground state of about 40%. © Owned by the authors, published by EDP Sciences, 2014.
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| 21. |
- Datta, U., et al.
(författare)
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Direct experimental evidence for a multiparticle-hole ground state configuration of deformed Mg-33
- 2016
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Ingår i: Physical Review C. - 2469-9985 .- 2469-9993. ; 94:3
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Tidskriftsartikel (refereegranskat)abstract
- The first direct experimental evidence of a multiparticle-hole ground state configuration of the neutron-rich Mg-33 isotope has been obtained via intermediate energy (400 A MeV) Coulomb dissociation measurement. The major part similar to(70 +/- 13)% of the cross section is observed to populate the excited states of Mg-32 after the Coulomb breakup of Mg-33. The shapes of the differential Coulomb dissociation cross sections in coincidence with different core excited states favor that the valence neutron occupies both the s(1/2) and p(3/2) orbitals. These experimental findings suggest a significant reduction and merging of sd-pf shell gaps at N similar to 20 and 28. The ground state configuration of Mg-33 is predominantly a combination of Mg-32(3.0,3.5MeV; 2(-), 1(-)) circle times nu(s1/2), Mg-32(2.5MeV; 2(+)) circle times nu(p3/2), and Mg-32(0; 0(+)) circle times nu(p3/2). The experimentally obtained quantitative spectroscopic information for the valence neutron occupation of the s and p orbitals, coupled with different core states, is in agreement with Monte Carlo shell model (MCSM) calculation using 3 MeV as the shell gap at N = 20.
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| 22. |
- Rahaman, A., et al.
(författare)
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Coulomb breakup of neutron-rich Na-29,Na-30 isotopes near the island of inversion
- 2017
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Ingår i: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 44:4, s. 045101-
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Tidskriftsartikel (refereegranskat)abstract
- First results are reported on the ground state configurations of the neutron-rich Na-29,Na-30 isotopes, obtained via Coulomb dissociation (CD) measurements. The invariant mass spectra of these nuclei have been obtained through measurement of the four-momenta of all decay products after Coulomb excitation of those nuclei on a Pb-208 target at energies of 400-430 MeV/nucleon using the FRS-ALADIN-LAND setup at GSI, Darmstadt. Integrated inclusive CD cross-sections (CD) of 89 (7) mb and 167 (13) mb for one neutron removal from Na-29 and Na-30, respectively, have been extracted up to an excitation energy of 10 MeV. The major part of one neutron removal, CD cross-sections of those nuclei populate the core, in its ground state. A comparison with the direct breakup model, suggests the predominant occupation of the valence neutron in the ground state of Na-29 (3/2(+)) and Na-30 (2(+)) is the d-orbital with a small contribution from the s-orbital, which are coupled with the ground state of the core. One of the major components of the ground state configurations of these nuclei are Na-28(gs)(1(+)) circle times v(s,d) and Na-29(gs)(3/2(+)) circle times v(s,d), respectively. The ground state spin and parity of these nuclei obtained from this experiment are in agreement with earlier reported values. The spectroscopic factors for the valence neutron occupying the s and d orbitals for these nuclei in the ground state have been extracted and reported for the first time. A comparison of the experimental findings with shell model calculation using the MCSM suggests a lower limit of around 4.3 MeV of the sd-pf shell gap in Na-30.
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| 23. |
- Röder, M., et al.
(författare)
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Coulomb dissociation of 20,21 N
- 2016
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Ingår i: Physical Review C - Nuclear Physics. - 2469-9985 .- 2469-9993 .- 0556-2813. ; 93:6
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Tidskriftsartikel (refereegranskat)abstract
- Neutron-rich light nuclei and their reactions play an important role in the creation of chemical elements. Here, data from a Coulomb dissociation experiment on N20,21 are reported. Relativistic N20,21 ions impinged on a lead target and the Coulomb dissociation cross section was determined in a kinematically complete experiment. Using the detailed balance theorem, the N19(n,γ)N20 and N20(n,γ)N21 excitation functions and thermonuclear reaction rates have been determined. The N19(n,γ)N20 rate is up to a factor of 5 higher at T
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| 24. |
- 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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| 25. |
- Bhattacharyya, A., et al.
(författare)
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Neutron capture cross sections of light neutron-rich nuclei relevant for -process nucleosynthesis
- 2021
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Ingår i: Physical Review C. - 2469-9993 .- 2469-9985. ; 104:4
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Tidskriftsartikel (refereegranskat)abstract
- The measurements of neutron capture cross sections of neutron-rich nuclei are challenging but essential for understanding nucleosynthesis and stellar evolution processes in the explosive burning scenario. In the quest of -process abundances, according to the neutrino-driven-wind model, light neutron-rich unstable nuclei may play a significant role as seed nuclei that influence the abundance pattern. Hence, experimental data for neutron capture cross sections of neutron-rich nuclei are needed. Coulomb dissociation of radioactive ion beams at intermediate energy is a powerful indirect method for inferring capture cross section. As a test case for validation of the indirect method, the neutron capture cross section (, ) for was inferred from the Coulomb dissociation of at intermediate energy ( MeV). A comparison between different theoretical approaches and experimental results for the reaction is discussed. We report for the first time experimental reaction cross sections of , , , and . The reaction cross sections were inferred indirectly through Coulomb dissociation of , , and at incident projectile energies around 400-430 MeV using the FRS-LAND setup at GSI, Darmstadt. The neutron capture cross sections were obtained from the photoabsorption cross sections with the aid of the detailed balance theorem. The reaction rates for the neutron-rich Na, Mg, Al nuclei at typical -process temperatures were obtained from the measured () capture cross sections. The measured neutron capture reaction rates of the neutron-rich nuclei, , , and are significantly lower than those predicted by the Hauser-Feshbach decay model. A similar trend was observed earlier for and but in the case of the trend is opposite. The situation is more complicated when the ground state has a multi-particle-hole configuration. For , the measured cross section is about higher than the Hauser-Feshbach prediction.
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| 26. |
- Boillos, J. M., et al.
(författare)
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Isotopic cross sections of fragmentation residues produced by light projectiles on carbon near
- 2022
-
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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| 27. |
- Chakraborty, S., et al.
(författare)
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Ground-state configuration of neutron-rich Al-35 via Coulomb breakup
- 2017
-
Ingår i: Physical Review C. - 2469-9985 .- 2469-9993. ; 96:3, s. 1965-
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Tidskriftsartikel (refereegranskat)abstract
- The ground-state configuration of Al-35 has been studied via Coulomb dissociation (CD) using the LAND-FRS setup (GSI, Darmstadt) at a relativistic energy of similar to 403 MeV/nucleon. The measured inclusive differential CD cross section for Al-35, integrated up to 5.0 MeV relative energy between the Al-34 core and the neutron using a Pb target, is 78(13) mb. The exclusive measured CD cross section that populates various excited states of 34Al is 29(7) mb. The differential CD cross section of Al-35 -> Al-34 + n has been interpreted in the light of a direct breakup model, and it suggests that the possible ground-state spin and parity of Al-35 could be, tentatively, 1/2+ or 3/2(+) or 5/2(+). The valence neutrons, in the ground state of Al-35, may occupy a combination of either l = 3,0 or l = 1,2 orbitals coupled with the Al-34 core in the ground and isomeric state(s), respectively. This hints of a particle-hole configuration of the neutron across the magic shell gaps at N = 20,28 which suggests narrowing the magic shell gap. If the 5/2+ is the ground-state spin-parity of Al-35 as suggested in the literature, then the major ground-state configuration of Al-35 is a combination of Al-34(g. s.; 4(-)) circle times upsilon(p3/2) and Al-34(isomer; 1(+)) circle times upsilon(d3/2) states. The result from this experiment has been compared with that from a previous knockout measurement and a calculation using the SDPF-M interaction.
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| 28. |
- Diaz Fernandez, Paloma, 1983, et al.
(författare)
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Quasifree (p, pN) scattering of light neutron-rich nuclei near N=14
- 2018
-
Ingår i: Physical Review C. - 2469-9985 .- 2469-9993. ; 97:2
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Tidskriftsartikel (refereegranskat)abstract
- Background: For many years, quasifree scattering reactions in direct kinematics have been extensively used to study the structure of stable nuclei, demonstrating the potential of this approach. The (RB)-B-3 collaboration has performed a pilot experiment to study quasifree scattering reactions in inverse kinematics for a stable C-12 beam. The results from that experiment constitute the first quasifree scattering results in inverse and complete kinematics. This technique has lately been extended to exotic beams to investigate the evolution of shell structure, which has attracted much interest due to changes in shell structure if the number of protons or neutrons is varied. Purpose: In this work we investigate for the first time the quasifree scattering reactions (p, pn) and (p, 2p) simultaneously for the same projectile in inverse and complete kinematics for radioactive beams with the aim to study the evolution of single-particle properties from N = 14 to N = 15. Method: The structure of the projectiles O-23, O-22, and N-21 has been studied simultaneously via (p, pn) and (p, 2p) quasifree knockout reactions in complete inverse kinematics, allowing the investigation of proton and neutron structure at the same time. The experimental data were collected at the (RB)-B-3-LAND setup at GSI at beam energies of around 400 MeV/u. Two key observables have been studied to shed light on the structure of those nuclei: the inclusive cross sections and the corresponding momentum distributions. Conclusions: The knockout reactions (p, pn) and (p, 2p) with radioactive beams in inverse kinematics have provided important and complementary information for the study of shell evolution and structure. For the (p, pn) channels, indications of a change in the structure of these nuclei moving from N = 14 to N = 15 have been observed, i.e., from the 0d(5/2) shell to the 1s(1/2). This supports previous observations of a subshell closure at N = 14 for neutron-rich oxygen isotopes and its weakening for the nitrogen isotopes.
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| 29. |
- Kirillova, Irina V., et al.
(författare)
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'Semi-dwarf' woolly mammoths from the East Siberian Sea coast, continental Russia
- 2020
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Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 49:2, s. 269-285
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Tidskriftsartikel (refereegranskat)abstract
- A pioneer comprehensive study of several diminutive last-generation woolly mammoth teeth (M3) found on the coast of the East Siberian Sea between the mouths of the Alazeya and Malaya Kuropatoch'ya rivers was conducted. Two teeth belonged to one individual. These teeth have a similar lamellar frequency and enamel thickness as teeth of Mammuthus primigenius Blumenbach. The molar crowns from the lower Alazeya region are similar in size to those of the small Late Pleistocene-Holocene mammoths from Wrangel Island. However, the number of plates (17-19, excluding talons) is much lower than that in the teeth of typical Late Pleistocene M. primigenius (23-25). The age data of the examined teeth are beyond the limits of the C-14 dating method (>45 000 years BP). Nevertheless, palaeobotanical data allow correlation of the enclosing sediments with the warm Kazantsevo Interglacial (Eemian, MIS 5e) and reconstruction of the average annual temperature, which was warmer than present-day temperatures. These conditions are confirmed by the delta O-18 isotopes from the structurally bound carbonate in tooth enamel. The ancient landscape was wetter and more forested than modern landscapes. The diminution of M3 size and loss of posterior plates were a result of the overall decrease in body size, likely in response to landscape change and narrowing of resource space. Mammoths from the lower Alazeya region demonstrate a stage of significant size reduction, although the dwarfing was not finalized. Their teeth are the oldest amongst the small teeth found in west Beringia.
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| 30. |
- Langer, C., et al.
(författare)
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Thermonuclear reaction S-30(p,gamma)Cl-31 studied via Coulomb breakup of Cl-31
- 2014
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Ingår i: Physical Review C - Nuclear Physics. - 2469-9985 .- 2469-9993. ; 89:3
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Tidskriftsartikel (refereegranskat)abstract
- Coulomb breakup at high energy in inverse kinematics of proton-rich Cl-31 was used to constrain the thermonuclear S-30(p,gamma)Cl-31 capture reaction rate under typical Type I x-ray burst conditions. This reaction is a bottleneck during rapid proton-capture nucleosynthesis (rp process), where its rate depends predominantly on the nuclear structure of Cl-31. Two low-lying states just above the proton-separation threshold of S-p = 296( 50) keV in Cl-31 have been identified experimentally using the (RB)-B-3-LAND setup at the GSI Helmholtzzentrum fur Schwerionenforschung GmbH. Both states are considered to play a key role in the thermonuclear S-30( p,gamma)Cl-31 capture reaction. Excitation energies of the first J(pi) = 1/2(+), 5/2(+) states have been extracted and the reaction rate for proton capture on S-30 under typical rp-process temperatures has been investigated.
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| 31. |
- Lehr, C., et al.
(författare)
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Unveiling the two-proton halo character of 17 Ne: Exclusive measurement of quasi-free proton-knockout reactions
- 2022
-
Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 827
-
Tidskriftsartikel (refereegranskat)abstract
- The proton drip-line nucleus 17Ne is investigated experimentally in order to determine its two-proton halo character. A fully exclusive measurement of the 17Ne(p,2p)16F→15⁎O+p quasi-free one-proton knockout reaction has been performed at GSI at around 500 MeV/nucleon beam energy. All particles resulting from the scattering process have been detected. The relevant reconstructed quantities are the angles of the two protons scattered in quasi-elastic kinematics, the decay of 16F into 15O (including γ decays from excited states) and a proton, as well as the 15O+p relative-energy spectrum and the 16F momentum distributions. The latter two quantities allow an independent and consistent determination of the fractions of l=0 and l=2 motion of the valence protons in 17Ne. With a resulting relatively small l=0 component of only around 35(3)%, it is concluded that 17Ne exhibits a rather modest halo character only. The quantitative agreement of the two values deduced from the energy spectrum and the momentum distributions supports the theoretical treatment of the calculation of momentum distributions after quasi-free knockout reactions at high energies by taking into account distortions based on the Glauber theory. Moreover, the experimental data allow the separation of valence-proton knockout and knockout from the 15O core. The latter process contributes with 11.8(3.1) mb around 40% to the total proton-knockout cross section of 30.3(2.3) mb, which explains previously reported contradicting conclusions derived from inclusive cross sections.
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| 32. |
- Marganiec, C., et al.
(författare)
-
Coulomb breakup of 17Ne from the viewpoint of nuclear astrophysics
- 2013
-
Ingår i: Proceedings of Science.
-
Konferensbidrag (refereegranskat)abstract
- By the Coulomb breakup of 17Ne, the time-reversed reaction 15O(2p,γ)17Ne has been studied. This reaction might play an important role in the rp process, as a break-out reaction of the hot CNO cycle. The secondary 17Ne ion beam with an energy of 500 MeV/nucleon has been dissociated in a Pb target. The reaction products have been detected with the LAND-R3B experimental setup at GSI. The preliminary differential and integral Coulomb dissociation cross section sCoul has been determined, which then will be converted into a photo-absorption cross section sphot o, and a two-proton radiative capture cross section σcap. Additionally, information about the structure of the 17Ne, a potential two-proton halo nucleus, will be received. The analysis is in progress.
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| 33. |
- Marganiec, J., et al.
(författare)
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Coulomb and nuclear excitations of narrow resonances in 17Ne
- 2016
-
Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 759, s. 200-205
-
Tidskriftsartikel (refereegranskat)abstract
- New experimental data for dissociation of relativistic 17Ne projectiles incident on targets of lead, carbon, and polyethylene targets at GSI are presented. Special attention is paid to the excitation and decay of narrow resonant states in 17Ne. Distributions of internal energy in the O15+p+p three-body system have been determined together with angular and partial-energy correlations between the decay products in different energy regions. The analysis was done using existing experimental data on 17Ne and its mirror nucleus 17N. The isobaric multiplet mass equation is used for assignment of observed resonances and their spins and parities. A combination of data from the heavy and light targets yielded cross sections and transition probabilities for the Coulomb excitations of the narrow resonant states. The resulting transition probabilities provide information relevant for a better understanding of the 17Ne structure.
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| 34. |
- Marganiec, J., et al.
(författare)
-
Coulomb breakup of 17Ne from the viewpoint of nuclear astrophysics
- 2012
-
Ingår i: Proceedings of Science. - Proceedings of Science : Sissa. - 1824-8039.
-
Konferensbidrag (refereegranskat)abstract
- By the Coulomb breakup of 17Ne, the time-reversed reaction 15O(2p,γ)17Ne has been studied. This reaction might play an important role in the rp process, as a break-out reaction of the hot CNO cycle. The secondary 17Ne ion beam with an energy of 500 MeV/nucleon has been dissociated in a Pb target. The reaction products have been detected with the LAND-R3B experimental setup at GSI. The preliminary differential and integral Coulomb dissociation cross section sCoul has been determined, which then will be converted into a photo-absorption cross section sphoto, and a two-proton radiative capture cross section σcap. Additionally, information about the structure of the 17Ne, a potential two-proton halo nucleus, will be received. The analysis is in progress. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.
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| 35. |
- Marganiec, J., et al.
(författare)
-
Studies of continuum states in (16) Ne using three-body correlation techniques
- 2015
-
Ingår i: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-601X .- 1434-6001. ; 51:1, s. 1-9
-
Tidskriftsartikel (refereegranskat)abstract
- Two-proton decay of the unbound nucleus Ne-16 , produced in one-neutron knockout from a 500 MeV/u Ne-17 beam, has been studied at GSI. The ground state, at a resonance energy 1.388(15) MeV, ( MeV) above the O-14 +p+p threshold, and two narrow resonances at MeV and 7.57(6) MeV have been investigated. A comparison of the energy difference between the first excited 2(+) state and the 0(+) ground state in Ne-16 with its mirror nucleus C-16 reveals a small Thomas-Ehrman shift (TES) of keV. A trend of the TES for the T = 2 quintet is obtained by completing the known data with a prediction for F-16 obtained from an IMME analysis. The decay mechanisms of the observed three resonances were revealed from an analysis of the energy and angular correlations of the O-14 +p+p decay products. The ground state decay can be considered as a genuine three-body (democratic) mode and the excited states decay sequentially via states in the intermediate nucleus F-15 , the 3.22 MeV state predominantly via the F-15 ground-state resonance, while the 7.57 MeV state decays via the 5/2(+) resonance in F-15 at 2.8 MeV above the O-14 +p+p threshold. Further, from an analysis of angular correlations, the spin-parity of the 7.57 MeV state has been determined as and assigned as the third 2(+) state in Ne-16 based on a comparison with C-16.
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| 36. |
- Revel, A., et al.
(författare)
-
Strong Neutron Pairing in core+4n Nuclei
- 2018
-
Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 120:15
-
Tidskriftsartikel (refereegranskat)abstract
- The emission of neutron pairs from the neutron-rich N=12 isotones C18 and O20 has been studied by high-energy nucleon knockout from N19 and O21 secondary beams, populating unbound states of the two isotones up to 15 MeV above their two-neutron emission thresholds. The analysis of triple fragment-n-n correlations shows that the decay N19(-1p)C18∗→C16+n+n is clearly dominated by direct pair emission. The two-neutron correlation strength, the largest ever observed, suggests the predominance of a C14 core surrounded by four valence neutrons arranged in strongly correlated pairs. On the other hand, a significant competition of a sequential branch is found in the decay O21(-1n)O20∗→O18+n+n, attributed to its formation through the knockout of a deeply bound neutron that breaks the O16 core and reduces the number of pairs.
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| 37. |
- Syndikus, I., et al.
(författare)
-
Probing the Z = 6 spin-orbit shell gap with (p,2p) quasi-free scattering reactions
- 2020
-
Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 809
-
Tidskriftsartikel (refereegranskat)abstract
- The evolution of the traditional nuclear magic numbers away from the valley of stability is an active field of research. Experimental efforts focus on providing key spectroscopic information that will shed light into the structure of exotic nuclei and understanding the driving mechanism behind the shell evolution. In this work, we investigate the Z=6 spin-orbit shell gap towards the neutron dripline. To do so, we employed NA(p,2p)CA−1 quasi-free scattering reactions to measure the proton component of the 21+ state of 16,18,20C. The experimental findings support the notion of a moderate reduction of the proton 1p1/2−1p3/2 spin-orbit splitting, at variance to recent claims for a prevalent Z=6 magic number towards the neutron dripline.
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| 38. |
- Uberseder, E., et al.
(författare)
-
First Experimental Constraint on the Fe-59(n, gamma)Fe-60 Reaction Cross Section at Astrophysical Energies via the Coulomb Dissociation of Fe-60
- 2014
-
Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 112:21
-
Tidskriftsartikel (refereegranskat)abstract
- The radionuclide Fe-60 has been of great interest to the nuclear astrophysics community for over a decade. An initial discrepancy between the observed and modeled Galactic Fe-60/Al-26 ratio motivated numerous studies focused on the nucleosynthesis of these two isotopes, though the cross section of the primary astrophysical production reaction, Fe-59(n,gamma)Fe-60, has remained purely theoretical. The present work offers a first experimental constraint on the Fe-59(n,gamma)Fe-60 cross section at astrophysical energies, obtained indirectly via Coulomb dissociation, and demonstrates that the theoretical reaction rates used in present stellar models are not highly erroneous.
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| 39. |
- Vandebrouck, M., et al.
(författare)
-
Effective proton-neutron interaction near the drip line from unbound states in F-25,F-26
- 2017
-
Ingår i: Physical Review C. - 2469-9985 .- 2469-9993. ; 96:5
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Odd-odd nuclei, around doubly closed shells, have been extensively used to study proton-neutron interactions. However, the evolution of these interactions as a function of the binding energy, ultimately when nuclei become unbound, is poorly known. The F-26 nucleus, composed of a deeply bound pi 0d(5/2) proton and an unbound v0d(3/2) neutron on top of an O-24 core, is particularly adapted for this purpose. The coupling of this proton and neutron results in a J(pi) = 1(1)(+) - 4(1)(+) multiplet, whose energies must be determined to study the influence of the proximity of the continuum on the corresponding proton-neutron interaction. The J(pi) = 1(1)(+), 2(1)(+), 4(1)(+) bound states have been determined, and only a clear identification of the J(pi) = 3(1)(+) is missing. Purpose: We wish to complete the study of the J(pi) = 1(1)(+) - 4(1)(+) multiplet in F-26, by studying the energy and width of the J(pi) = 3(1)(+) unbound state. The method was first validated by the study of unbound states in F-25, for which resonances were already observed in a previous experiment. Method: Radioactive beams of Ne-26 and Ne-27, produced at about 440AMeV by the fragment separator at the GSI facility were used to populate unbound states in F-25 and F-26 via one-proton knockout reactions on a CH2 target, located at the object focal point of the (RB)-B-3/LAND setup. The detection of emitted. rays and neutrons, added to the reconstruction of the momentum vector of the A - 1 nuclei, allowed the determination of the energy of three unbound states in F-25 and two in F-26. Results: Based on its width and decay properties, the first unbound state in F-25, at the relative energy of 49(9) keV, is proposed to be a J(pi) = 1/ 2(-) arising from a p1/2 proton- hole state. In F-26, the first resonance at 323(33) keV is proposed to be the J(pi) = 3(1)(+) member of the J(pi) = 1(1)(+) - 4(1)(+) multiplet. Energies of observed states in F-25,F-26 have been compared to calculations using the independent-particle shell model, a phenomenological shell model, and the ab initio valence-space in-medium similarity renormalization group method. Conclusions: The deduced effective proton- neutron interaction is weakened by about 30-40% in comparison to the models, pointing to the need for implementing the role of the continuum in theoretical descriptions or to a wrong determination of the atomic mass of F-26.
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| 40. |
- Wamers, F., et al.
(författare)
-
Comparison of electromagnetic and nuclear dissociation of Ne-17
- 2018
-
Ingår i: Physical Review C. - : AMER PHYSICAL SOC. - 2469-9985 .- 2469-9993. ; 97:3
-
Tidskriftsartikel (refereegranskat)abstract
- The Borromean drip-line nucleus Ne-17 has been suggested to possess a two-proton halo structure in its ground state. In the astrophysical rp-process, where the two-proton capture reaction O-15(2p,gamma) Ne-17 plays an important role, the calculated reaction rate differs by several orders of magnitude between different theoretical approaches. To add to the understanding of the Ne-17 structure we have studied nuclear and electromagnetic dissociation. A 500 MeV/u Ne-17 beam was directed toward lead, carbon, and polyethylene targets. Oxygen isotopes in the final state were measured in coincidence with one or two protons. Different reaction branches in the dissociation of Ne-17 were disentangled. The relative populations of s and d states in F-16 were determined for light and heavy targets. The differential cross section for electromagnetic dissociation (EMD) shows a continuous internal energy spectrum in the three-body system O-15 + 2p. The Ne-17 EMD data were compared to current theoretical models. None of them, however, yields satisfactory agreement with the experimental data presented here. These new data may facilitate future development of adequate models for description of the fragmentation process.
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| 41. |
- Wamers, F., et al.
(författare)
-
Comparison of electromagnetic and nuclear dissociation of Ne 17
- 2018
-
Ingår i: Physical Review C. - 2469-9985 .- 2469-9993. ; 97:3
-
Tidskriftsartikel (refereegranskat)abstract
- The Borromean drip-line nucleus Ne17 has been suggested to possess a two-proton halo structure in its ground state. In the astrophysical rp-process, where the two-proton capture reaction O15(2p,γ)Ne17 plays an important role, the calculated reaction rate differs by several orders of magnitude between different theoretical approaches. To add to the understanding of the Ne17 structure we have studied nuclear and electromagnetic dissociation. A 500 MeV/u Ne17 beam was directed toward lead, carbon, and polyethylene targets. Oxygen isotopes in the final state were measured in coincidence with one or two protons. Different reaction branches in the dissociation of Ne17 were disentangled. The relative populations of s and d states in F16 were determined for light and heavy targets. The differential cross section for electromagnetic dissociation (EMD) shows a continuous internal energy spectrum in the three-body system O15+2p. The Ne17 EMD data were compared to current theoretical models. None of them, however, yields satisfactory agreement with the experimental data presented here. These new data may facilitate future development of adequate models for description of the fragmentation process.
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| 42. |
- Wamers, F., et al.
(författare)
-
Diverse mechanisms in proton knockout reactions from the Borromean nucleus Ne-17
- 2023
-
Ingår i: European Physical Journal A. - : Springer. - 1434-6001 .- 1434-601X. ; 59
-
Tidskriftsartikel (refereegranskat)abstract
- Nucleon knockout experiments using beryllium or carbon targets reveal a strong dependence of the quenching factors, i.e., the ratio (Rs) of theoretical to the experimental spectroscopic factors (C2S), on the proton-neutron asymmetry in the nucleus under study. However, this dependence is greatly reduced when a hydrogen target is used. To understand this phenomenon, exclusive H-1(Ne-17, 2p F-16) and inclusive C-12(Ne-17, 2p 1(6)F)X, 1(2)C(Ne-17, F-16)X as well as 1H(Ne-17,(16) F)X(X-denotes undetected reaction products) reactions with F-16 in the ground and excited states were anal- ysed. The longitudinal momentum distribution of F-16 and the correlations between the detached protons were studied. In the case of the carbon target, there is a significant deviation from the predictions of the eikonal model. The eikonal approximation was used to extract spectroscopic factor values (CS)-S-2. The experimental (CS)-S-2 value obtained with C target is markedly lower than that for H target. This is interpreted as rescattering due to simultaneous nucleon knockout from both reaction partners, Ne-17 and C-12.
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| 43. |
- Wamers, F., et al.
(författare)
-
First Observation of the Unbound Nucleus Ne-15
- 2014
-
Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 112:13
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the first observation of the unbound proton-rich nucleus Ne-15. Its ground state and first excited state were populated in two-neutron knockout reactions from a beam of 500 MeV/u Ne-17. The Ne-15 ground state is found to be unbound by 2.522(66) MeV. The decay proceeds directly to O-13 with simultaneous two-proton emission. No evidence for sequential decay via the energetically allowed 2(-) and 1(-) states in F-14 is observed. The Ne-15 ground state is shown to have a strong configuration with two protons in the (sd) shell around O-13 with a 63(5)% (1s(1/2))(2) component.
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| 44. |
- Wamers, F., et al.
(författare)
-
New insight into knockout reactions from the two-proton halo nucleus Ne 17
- 2024
-
Ingår i: Physical Review C. - 2469-9985 .- 2469-9993. ; 109:5
-
Tidskriftsartikel (refereegranskat)abstract
- Background: The unexplained disagreement in the dependence of spectroscopic factors (C2Sexp) on the binding energy obtained by nucleon knockout using different targets is still a puzzle that needs to be addressed. Purpose: To find an explanation of this riddle through exclusive measurements using different targets. Method: The exclusive measurements were performed by using a Ne17 beam with an energy of 500 MeV/u incident on C and CH2 targets. Through the standard theoretical approach, C2Sexp were derived from the analysis of the experimental data on proton ejection from the proton halo in Ne17 as well as from its core O15. Result: For the C target, proton ejection from the proton halo gave C2Sexp about 37% smaller than for the H target. But when protons are ejected from the core of Ne17, C2Sexp are identical within statistical uncertainties. Conclusion: An explanation for the difference in C2Sexp could be the removal of both halo protons, a more important reaction pathway for the C target. The C2Sexp values obtained by analyzing the proton ejection from the core indicate that it is not affected by the interaction with the halo protons.
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| 45. |
- Aksouh, F., et al.
(författare)
-
STUDY OF THE O-15(2p,gamma)Ne-17 CROSS SECTION BY COULOMB DISSOCIATION OF Ne-17 FOR THE rp PROCESS OF NUCLEOSYNTHESIS
- 2014
-
Ingår i: Acta Physica Polonica, Series B.. - 1509-5770 .- 0587-4254. ; 45:2, s. 229-234
-
Tidskriftsartikel (refereegranskat)abstract
- The O-15(2p, gamma)Ne-17 cross section has been studied by the inverse reaction, the Coulomb dissociation of Ne-17. The experiment has been performed at the GSI. The Ne-17 excitation energy prior to decay has been reconstructed by using the invariant-mass method. The preliminary differential and integral Coulomb dissociation cross sections (sigma(Coul)) have been extracted, which provide a photoabsorption (sigma(photo)) and a radiative capture cross section (sigma(cap)). Additionally, important information about the Ne-17 nuclear structure will be obtained. The analysis is in progress.
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| 46. |
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| 47. |
- Efimova, M. O., et al.
(författare)
-
Luminescence dating of the MIS 6 glaciation of the Pamir mountains (Central Asia)
- 2024
-
Ingår i: Quaternary Geochronology. - : Elsevier. - 1871-1014 .- 1878-0350. ; 83
-
Tidskriftsartikel (refereegranskat)abstract
- The Pamir Mountains are one of the highest mountain systems in the world; they act as sources of fresh water for the main rivers of Central Asia: the Amudaria and Syrdaria. Throughout the Quaternary, the Pamirs played a major role in controlling atmospheric circulation and land-surface processes, and provided great volumes of terrigenous sediments for transport by large rivers to the depressions in the Aral and Caspian regions. These ultimately provided broad aeolian cover in the sandy deserts, and finer dust for the widely distributed loesspalaeosol sequences. The glaciation history of this highly dynamic region provides an important basis for understanding climate change, sediment source and landscape evolution in Central Asia during the Quaternary. The question of the number, distribution, extent and timing of Pleistocene glaciations in the Pamir is debated. One of the main obstacles to research, together with difficulties of access and severity of current climate, is the varying degree of preservation of traces of previous glaciations in the western and eastern Pamir. As a result of a geological survey, we for the first time identified a thick lacustrine deposit at high altitudes in a tributary of the Panj - the valley of the Sary-Shitharv River - this records the damming of the Panj River valley by a large glacier. Luminescence measurements were undertaken to obtain the age of the Sary-Shitharv glacially-dammed lake. As often in mountain catchments the quartz OSL signal was unsuitable for dose estimation, and so the chronology of the Sary-Shitharv section is based entirely on post-IR IRSL signals from K-rich feldspar. We used pIRIR50,290 and pIRIR200,290 protocols and obtained indistinguishable ages from both protocols. Given the high sedimentation rates deduced from the structure of lacustrine deposits, the entire sequence must have been accumulated rather quickly, over a period of no more than a few thousand years. The average age over the whole series of dates is 165 +/- 11 ka. This places the existence of the glacially-dammed lake at Sary-Shitharv in late MIS 6, a result that fits well with the general course of the glacial history of the Pamirs.
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| 48. |
- Holl, Matthias, 1986, et al.
(författare)
-
Border of the island of inversion: Unbound states in Ne-29
- 2022
-
Ingår i: Physical Review C. - 2469-9985 .- 2469-9993. ; 105:3
-
Tidskriftsartikel (refereegranskat)abstract
- The nucleus Ne-29 is situated at the border of the island of inversion. Despite significant efforts, no bound low-lying intruder f(7/2) state, which would place Ne-29 firmly inside the island of inversion, has yet been observed. Here, the first investigation of unbound states of Ne-29 is reported. The states were populated in Ne-30(p, pn) and Na-30(p, 2p) reactions at a beam energy of around 230 MeV/nucleon, and analyzed in terms of their resonance properties, partial cross sections, and momentum distributions. The momentum distributions are compared to calculations using the eikonal, direct reaction model, allowing assignments for the observed states. The lowest lying resonance at an excitation energy of 1.48(4) MeV shows clear signs of a significant l = 3 component, giving first evidence for f(7/2) single particle strength in Ne-29. The excitation energies and strengths of the observed states are compared to shell-model calculations using the SDPF-U-MIX interaction.
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| 49. |
- Holl, M., et al.
(författare)
-
Quasi-free neutron and proton knockout reactions from light nuclei in a wide neutron-to-proton asymmetry range
- 2019
-
Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 795, s. 682-688
-
Tidskriftsartikel (refereegranskat)abstract
- The quasi-free scattering reactions 11C(p,2p) and 10,11,12C(p,pn) have been studied in inverse kinematics at beam energies of 300–400 MeV/u at the R3B-LAND setup. The outgoing proton-proton and proton-neutron pairs were detected in coincidence with the reaction fragments in kinematically complete measurements. The efficiency to detect these pairs has been obtained from GEANT4 simulations which were tested using the 12C(p,2p) and 12C(p,pn) reactions. Experimental cross sections and momentum distributions have been obtained and compared to DWIA calculations based on eikonal theory. The new results reported here are combined with previously published cross sections for quasi-free scattering from oxygen and nitrogen isotopes and together they enable a systematic study of the reduction of single-particle strength compared to predictions of the shell model over a wide neutron-to-proton asymmetry range. The combined reduction factors show a weak or no dependence on isospin asymmetry, in contrast to the strong dependency reported in nucleon-removal reactions induced by nuclear targets at lower energies. However, the reduction factors for (p,2p) are found to be 'significantly smaller than for (p,pn) reactions for all investigated nuclei.
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| 50. |
- Kondo, Y., et al.
(författare)
-
First observation of 28 O
- 2023
-
Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 620:7976, s. 965-970
-
Tidskriftsartikel (refereegranskat)abstract
- Subjecting a physical system to extreme conditions is one of the means often used to obtain a better understanding and deeper insight into its organization and structure. In the case of the atomic nucleus, one such approach is to investigate isotopes that have very different neutron-to-proton (N/Z) ratios than in stable nuclei. Light, neutron-rich isotopes exhibit the most asymmetric N/Z ratios and those lying beyond the limits of binding, which undergo spontaneous neutron emission and exist only as very short-lived resonances (about 10−21s), provide the most stringent tests of modern nuclear-structure theories. Here we report on the first observation of 28O and 27O through their decay into 24O and four and three neutrons, respectively. The 28O nucleus is of particular interest as, with the Z = 8 and N = 20 magic numbers1,2, it is expected in the standard shell-model picture of nuclear structure to be one of a relatively small number of so-called ‘doubly magic’ nuclei. Both 27O and 28O were found to exist as narrow, low-lying resonances and their decay energies are compared here to the results of sophisticated theoretical modelling, including a large-scale shell-model calculation and a newly developed statistical approach. In both cases, the underlying nuclear interactions were derived from effective field theories of quantum chromodynamics. Finally, it is shown that the cross-section for the production of 28O from a 29F beam is consistent with it not exhibiting a closed N = 20 shell structure.
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