SwePub - sökning: WFRF:(Törnqvist Hans 1985)

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1.	Storck, Sonja, et al. (författare) Lifetime measurement of the 26 0 g.s. At SAMURAI 2020 Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 1643:1 Konferensbidrag (refereegranskat)abstract The ground state of the neutron unbound nucleus O is speculated to have a lifetime in the pico-second regime. In order to determine the decay lifetime of the O ground state with high sensitivity and precision, a new method has been applied. The experiment was performed in December 2016 at the Superconducting Analyzer for MUlti-particle from Radio Isotope Beams (SAMURAI) at the Radioactive Isotope Beam Factory (RIBF) at RIKEN. A F beam was produced in the fragment separator BigRIPS and impinged on a W/Pt target stack where O was produced. According to the lifetime, the decay of O happens either in or outside the target. Thus, the velocity difference between the decay neutrons and the fragment O delivers a characteristic spectrum from which the lifetime can be extracted.
2.	Audouin, L., et al. (författare) High-precision measurement of isotopic fission yields of 236 U 2018 Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. ; 193 Konferensbidrag (refereegranskat)abstract We report on the second SOFIA experiment, dedicated to the fission yields of 236U∗, analog to 235U(n,f). The measurement is based on the inverse kinematics method, using a relativistic, secondary beam of 236U. Both fission fragments are identified in mass and charge in the SOFIA recoil spectrometer. The obtained isotopic yields are compared with existing spectroscopy measurements and the elemental yields are used to discuss the treatment of the even-odd effect with energy in nuclear data libraries.
3.	Boretzky, K., et al. (författare) NeuLAND: The high-resolution neutron time-of-flight spectrometer for R 3 B at FAIR 2021 Ingår i: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002. ; 1014 Tidskriftsartikel (refereegranskat)abstract NeuLAND (New Large-Area Neutron Detector) is the next-generation neutron detector for the R3B (Reactions with Relativistic Radioactive Beams) experiment at FAIR (Facility for Antiproton and Ion Research). NeuLAND detects neutrons with energies from 100 to 1000 MeV, featuring a high detection efficiency, a high spatial and time resolution, and a large multi-neutron reconstruction efficiency. This is achieved by a highly granular design of organic scintillators: 3000 individual submodules with a size of 5 × 5 × 250 cm3 are arranged in 30 double planes with 100 submodules each, providing an active area of 250 × 250 cm2 and a total depth of 3 m. The spatial resolution due to the granularity together with a time resolution of σt≤ 150 ps ensures high-resolution capabilities. In conjunction with calorimetric properties, a multi-neutron reconstruction efficiency of 50% to 70% for four-neutron events will be achieved, depending on both the emission scenario and the boundary conditions allowed for the reconstruction method. We present in this paper the final design of the detector as well as results from test measurements and simulations on which this design is based.
4.	Gobel, K., et al. (författare) Coulomb dissociation of 16O into 4He and 12C 2020 Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 1668:1 Konferensbidrag (refereegranskat)abstract We measured the Coulomb dissociation of 16O into 4He and 12C at the R3B setup in a first campaign within FAIR Phase 0 at GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt. The goal was to improve the accuracy of the experimental data for the 12C(a,?)16O fusion reaction and to reach lower center-ofmass energies than measured so far. The experiment required beam intensities of 109 16O ions per second at an energy of 500 MeV/nucleon. The rare case of Coulomb breakup into 12C and 4He posed another challenge: The magnetic rigidities of the particles are so close because of the same mass-To-charge-number ratio A/Z = 2 for 16O, 12C and 4He. Hence, radical changes of the R3B setup were necessary. All detectors had slits to allow the passage of the unreacted 16O ions, while 4He and 12C would hit the detectors' active areas depending on the scattering angle and their relative energies. We developed and built detectors based on organic scintillators to track and identify the reaction products with sufficient precision.
5.	Graña-González, A., et al. (författare) Quasi-free (p,2p) reactions in inverse kinematics for studying the fission yield dependence on temperature 2023 Ingår i: FAIR next generation scientists - 7th Edition Workshop : FAIRness2022 - FAIRness2022. - 1824-8039. ; 419 Konferensbidrag (refereegranskat)abstract Despite the recent experimental and theoretical progress in the investigation of the nuclear fission process, a complete description still represents a challenge in nuclear physics because it is a very complex dynamical process, whose description involves the coupling between intrinsic and collective degrees of freedom, as well as different quantum-mechanical phenomena. To improve on the existing data on nuclear fission, we produce fission reactions of heavy nuclei in inverse kinematics by using quasi-free (p,2p) scattering, which induce fission through particle-hole excitations that can range from few to ten's of MeV. The measurement of the four-momenta of the two outgoing protons allows to reconstruct the excitation energy of the fissioning compound nucleus and therefore to study the evolution of the fission yields with temperature. The realization of this kind of experiment requires a complex experimental setup, providing full isotopic identification of both fission fragments and an accurate measurement of the momenta of the two outgoing protons. This was realized recently at the GSI/FAIR facility and here some preliminary results are presented.
6.	Johansen, J. G., et al. (författare) Experimental study of bound states in Be-12 through low-energy Be-11(d,p)-transfer reactions 2013 Ingår i: Physical Review C - Nuclear Physics. - 2469-9985 .- 2469-9993. ; 88:4 Tidskriftsartikel (refereegranskat)abstract The bound states of Be-12 have been studied through a Be-11(d, p) Be-12 transfer reaction experiment in inverse kinematics. A 2.8 MeV/u beam of Be-11 was produced using the REX-ISOLDE facility at CERN. The outgoing protons were detected with the T-REX silicon detector array. The MINIBALL germanium array was used to detect gamma rays from the excited states in Be-12. The gamma-ray detection enabled a clear identification of the four known bound states in Be-12, and each of the states has been studied individually. Differential cross sections over a large angular range have been extracted. Spectroscopic factors for each of the states have been determined from distorted wave Born approximation (DWBA) calculations and have been compared to previous experimental and theoretical results.
7.	Johansen, Jacob G., et al. (författare) Study of bound states in 10Be by one neutron removal reactions of 11Be 2017 Ingår i: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 44:4 Tidskriftsartikel (refereegranskat)abstract The bound states of 10Be have been studied by removing single neutrons from 11Be nuclei. A 2.8 MeV u-1 beam of 11Be was produced at ISOLDE, CERN and directed on to both proton and deuteron targets inducing one-neutron removal reactions. Charged particles were detected to identify the two reaction channels (d, t) and (p, d), and the individual states in 10Be were identified by gamma detection. All bound states but one were populated and identified in the (d, t) reaction. The combination of REX-ISOLDE and MINIBALL allowed for a clean separation of the high-lying states in 10Be. This is the first time these states have been separated in a reaction experiment. Differential cross sections have been calculated for all the reaction channels and compared to DWBA calculations. Spectroscopic factors are derived and compared to values from the litterature. While the overall agreement between the spectrocopic factors is poor, the ratio between the ground state and the first excited state is in agreement with the previous measured ones. Furthermore, a significant population of the state is observed, which which may indicate the presence of multi-step processes at our beam energy.
8.	Johansson, Håkan T, 1977, et al. (författare) TRLO II - friendly FPGA trigger control 2014 Ingår i: GSI Scientific Report 2013. - 0171-4546. ; 2014-1, s. 354- Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
9.	Kirsebom, O. S., et al. (författare) First Accurate Normalization of the β -delayed α Decay of N 16 and Implications for the C 12 (α,γ) O 16 Astrophysical Reaction Rate 2018 Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 121:14 Tidskriftsartikel (refereegranskat)abstract Published by the American Physical Society. The C12(α,γ)O16 reaction plays a central role in astrophysics, but its cross section at energies relevant for astrophysical applications is only poorly constrained by laboratory data. The reduced α width, γ11, of the bound 1- level in O16 is particularly important to determine the cross section. The magnitude of γ11 is determined via sub-Coulomb α-transfer reactions or the β-delayed α decay of N16, but the latter approach is presently hampered by the lack of sufficiently precise data on the β-decay branching ratios. Here we report improved branching ratios for the bound 1- level [bβ,11=(5.02±0.10)×10-2] and for β-delayed α emission [bβα=(1.59±0.06)×10-5]. Our value for bβα is 33% larger than previously held, leading to a substantial increase in γ11. Our revised value for γ11 is in good agreement with the value obtained in α-transfer studies and the weighted average of the two gives a robust and precise determination of γ11, which provides significantly improved constraints on the C12(α,γ) cross section in the energy range relevant to hydrostatic He burning.
10.	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.
11.	Kudaibergenova, E., et al. (författare) MEASUREMENTS OF THE REACTION CROSS SECTIONS OF NEUTRON-RICH Sn ISOTOPES AT THE R 3 B SETUP 2024 Ingår i: Acta Physica Polonica B, Proceedings Supplement. - 1899-2358. ; 17:3 Tidskriftsartikel (refereegranskat)abstract A fundamental framework to describe nuclear matter as a function of pressure and nuclear isospin asymmetry is the nuclear Equation of State (EoS). Constraining the parameters of the EoS is one of the central issues in nuclear physics, especially since the slope parameter L has not yet been constrained well experimentally. It has been identified that a precise determination of the neutron-removal cross section in neutron-rich nuclei, which correlates with the neutron-skin thickness, would provide a more precise constraint on L. To this end, an experiment was performed at the R3B setup in the GSI Helmholtzzentrum für Schwerionenforschung GmbH as a part of the FAIR Phase-0 program. The reactions are studied in inverse kinematics with neutron-rich tin isotopes in the mass range of A = 124–134 on carbon targets of different thicknesses. The reaction products have been measured at beam energies of 400–900 MeV/u in a kinematically complete manner. In this communication, the analysis of124Sn+12C at 900 MeV/u is presented. The charge-exchange reactions, resulting processes, and their role in the calculation of other reaction cross sections are discussed.
12.	Lihtar, I., et al. (författare) RELATIVISTIC COULOMB EXCITATION OF 124 Sn 2024 Ingår i: Acta Physica Polonica B, Proceedings Supplement. - 1899-2358. ; 17:3 Tidskriftsartikel (refereegranskat)abstract The Coulomb excitation of 124, 128, 130, 132, 134Sn isotopes in the electric field of a Pb target have been studied using the R3B setup as a part of the FAIR Phase-0 program. The experiment was motivated by the possibility of using the nuclear dipole response to infer valuable information on the slope of the symmetry energy of the nuclear equation of state. Measurements were performed in inverse kinematics at relativistic energies of 750 MeV/u and 904 MeV/u. The analysis method and preliminary results for the decay channel with a single outgoing neutron for 124Sn are reported.
13.	Löher, B., et al. (författare) The DAQ readout library vmelib 2015 Ingår i: GSI Scientific Report 2014. - 0171-4546. ; 2015-1, s. 192- Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
14.	Ponnath, L., et al. (författare) Measurement of nuclear interaction cross sections towards neutron-skin thickness determination 2024 Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 855 Tidskriftsartikel (refereegranskat)abstract The accuracy of reaction theories used to extract properties of exotic nuclei from scattering experiments is often unknown or not quantified, but of utmost importance when, e.g., constraining the equation of state of asymmetric nuclear matter from observables as the neutron-skin thickness. In order to test the Glauber multiple-scattering model, the total interaction cross section of [Formula presented] on carbon targets was measured at initial beam energies of 400, 550, 650, 800, and 1000 MeV/nucleon. The measurements were performed during the first experiment of the newly constructed R3B (Reaction with Relativistic Radioactive Beams) experiment after the start of FAIR Phase-0 at the GSI/FAIR facility with beam energies of 400, 550, 650, 800, and 1000 MeV/nucleon. The combination of the large-acceptance dipole magnet GLAD and a newly designed and highly efficient Time-of-Flight detector enabled a precise transmission measurement with several target thicknesses for each initial beam energy with an experimental uncertainty of ±0.4%. A comparison with the Glauber model revealed a discrepancy of around 3.1% at higher beam energies, which will serve as a crucial baseline for the model-dependent uncertainty in future fragmentation experiments.
15.	Törnqvist, Hans, 1985, et al. (författare) Implementation and evaluation of tilted foils polarization at REX-ISOLDE 2012 Ingår i: Physica Scripta. - 1402-4896 .- 0031-8949. ; T150:T150 Tidskriftsartikel (refereegranskat)abstract The progress within atomic and nuclear physics relies on refining and adding new observables. One of these is the polarization of the nuclear spin, where there is a manifest interest in accessing a wide variety of polarized beams, e. g. at energies suitable for Coulomb excitation and transfer experiments. In particular, exotic nuclei with half-lives considerably less than one second are difficult to produce, but the issues present in traditional methods could be overcome by using the tilted foils technique. Two setups for measuring the degree of polarization of an ion beam after the REX-ISOLDE linear accelerator at CERN are being evaluated. An approach based on Coulomb excitation has been utilized in an experiment and preliminary results will be presented. Furthermore, a beta-NMR setup is currently under construction that will take radioactive beams soon.
16.	Törnqvist, Hans, 1985 (författare) Tilted Foils Nuclear Spin Polarization and Measurement with Coulomb Excitation 2012 Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract Developing new experimental tools is essential to expand the possibilites of probing the structure of atomic nuclei. The better the currently known properties of nuclei can be manipulated, the more information can be extracted from data collected in nuclear reaction experiments. One property that has been controlled for many years is the nuclear spin, but this has only been viable for a certain set of isotopes with restrictions on for example specific atomic excitation schemes or half-lives.This thesis will provide details on an evaluation project using thin tilted foils after the REX-ISOLDE linac at the CERN-ISOLDE experimental facility, to polarize the spin of nuclei in-flight. The nuclear polarization is then measured with a technique based on Coulomb excitation, which is a flexible and readily available experimental method at ISOLDE with the MINIBALL spectrometer. The tilted foils technique may be beneficial to polarize the nuclear spin of short-lived radioactive beams that can be difficult by other means. The only restrictions on the accelerated ions known so far to produce polarization with tilted foils are non-zero nuclear and atomic spin.The $\beta$-NMR is an alternative, more common technique for measuring nuclear spin polarization. No such setup connected to REX-ISOLDE existed at the start of the project which prompted for the Coulomb excitation method with MINIBALL. Although, a $\beta$-NMR setup is currently under construction and testing.
17.	Törnqvist, Hans, 1985 (författare) Tilted Foils Nuclear Spin Polarization at REX-ISOLDE 2013 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract This thesis will explain and summarize my work and involvement in experiments aimed at producing nuclear spin polarization of post-accelerated beams of ions with the tilted-foils technique at the REX-ISOLDE linear accelerator at CERN. Polarizing the nuclear spin of radioactive beams in particular may provide access to observables which may be difficult to obtain otherwise. Currently, the techniques commonly employed for nuclear spin polarization are restricted to specific nuclides and experimental measurement techniques. Tilted foils polarization may provide a new tool to extend the range of nuclides that can be polarized and the types of experiments that can be performed.The experiments rely not only on the production but also on the method to measure the degree of attained polarization. Two methods will be treated, based on particle scattering in Coulomb excitation that may be utilized for stable beams, and the beta-NMR that requires beta-decaying nuclei. The experimental setups and measurements will be described with interpretation of collected data and final results.Experiments have already been proposed utilizing the setup developed for this project. Furthermore, since the tilted foils polarization technique may be a tool to produce a new range of polarized beams at the upcoming HIE-ISOLDE facility, and is most efficient with low energy beams, post-acceleration of the beam is of major interest. Reaching the intermediary energy range after post-acceleration may allow Coulomb excitation and transfer experiments to use polarized beams of exotic isotopes. The thesis will conclude with initial studies for post-acceleration at the HIE-ISOLDE linac.
18.	Törnqvist, Hans, 1985, et al. (författare) Tilted foils polarization at REX-ISOLDE 2013 Ingår i: Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms. - : Elsevier BV. - 0168-583X. ; 317:PART B, s. 685-688 Tidskriftsartikel (refereegranskat)abstract The tilted-foils nuclear-spin polarization method has been evaluated using the REX-ISOLDE linear accelerator at the ISOLDE facility, CERN. A beam of 8Li delivered with an energy of 300 keV/u traversed through one Mylar foil to degrade the beam energy to 200 keV/u and consequently through 10 thin diamond-like carbon foils to polarize the nuclear spin. The attained nuclear spin polarization of 3.6±0.3% was measured with a β-NMR setup.
19.	Wang, H., et al. (författare) Intruder configurations in 29 Ne at the transition into the island of inversion: Detailed structure study of 28 Ne 2023 Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 843 Tidskriftsartikel (refereegranskat)abstract Detailed γ-ray spectroscopy of the exotic neon isotope 28Ne has been performed for the first time using the one-neutron removal reaction from 29Ne on a liquid hydrogen target at 240 MeV/nucleon. Based on an analysis of parallel momentum distributions, a level scheme with spin-parity assignments has been constructed for 28Ne and the negative-parity states are identified for the first time. The measured partial cross sections and momentum distributions reveal a significant intruder p-wave strength providing evidence of the breakdown of the N=20 and N=28 shell gaps. Only a weak, possible f-wave strength was observed to bound final states. Large-scale shell-model calculations with different effective interactions do not reproduce the large p-wave and small f-wave strength observed experimentally, indicating an ongoing challenge for a complete theoretical description of the transition into the island of inversion along the Ne isotopic chain.
20.	Xarepe, M., et al. (författare) Resistive plate chambers for precise measurement of high-momentum protons in short range correlations at R 3 B 2023 Ingår i: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - 0168-9002. ; 1055 Tidskriftsartikel (refereegranskat)abstract The Reactions with Relativistic Radioactive Beams (R3B) collaboration of the Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany, has constructed an experimental setup to perform fundamental studies of nuclear matter, using as a probe reactions with exotic nuclei at relativistic energies. Among the various detection systems, one of the most recent upgrades consists of the installation of a large area, around 2 m2, multi-gap Resistive Plate Chamber (RPC). The chamber is equipped with twelve 0.3mm gaps and readout by 30mm pitch strips, exhibiting a timing precision down to 50 ps and efficiencies above 98% for minimum ionizing particles in a previous characterization of the detector. The RPC was part of the setup of the FAIR Phase 0 experiment that focused on measuring for the first time, in spring 2022, nucleon–nucleon short-range correlations (SRC) inside an exotic nucleus (16C). The excellent timing precision of this detector will allow the measurement of the forward emitted proton momentum with a resolution of around 1%. In beam measurements show an RPC efficiency above 95% and a time precision better than 100 ps (including the contribution of a reference scintillator and the momentum spread of the particles) for forward emitted particles.

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