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Sökning: WFRF:(Fissum K.)

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1.
  • Singh, B. P., et al. (författare)
  • Experimental access to Transition Distribution Amplitudes with the PANDA experiment at FAIR
  • 2015
  • Ingår i: European Physical Journal A. Hadrons and Nuclei. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 51:8
  • Tidskriftsartikel (refereegranskat)abstract
    • Baryon-to-meson Transition Distribution Amplitudes (TDAs) encoding valuable new information on hadron structure appear as building blocks in the collinear factorized description for several types of hard exclusive reactions. In this paper, we address the possibility of accessing nucleon-to-pion (pi N) TDAs from (p) over barp -> e(+)e(-)pi(0) reaction with the future PANDA detector at the FAIR facility. At high center-of-mass energy and high invariant mass squared of the lepton pair q(2), the amplitude of the signal channel (p) over barp -> e(+)e(-)pi(0) admits a QCD factorized description in terms of pi N TDAs and nucleon Distribution Amplitudes (DAs) in the forward aid backward kinematic regimes. Assuming the validity of this factorized description, we perform feasibility studies for measuring (p) over barp -> e(+)e(-)pi(0) with the PANDA detector. Detailed simulations on signal reconstruction efficiency as well as on rejection of the most severe background channel, i.e. (p) over barp -> pi(+)pi(-)pi(0) were performed for the center-of-mass energy squared s = 5 GeV2 and s = 10 GeV2, in the kinematic regions 3.0 < q(2) < 4.3 GeV2 and 5 < q(2) < 9 GeV2, respectively, with a neutral pion scattered in the forward or backward cone vertical bar cos theta(pi 0)vertical bar > 0.5 in the proton-antiproton center-of-mass frame. Results of the simulation show that the particle identification capabilities of the PANDA detector will allow to achieve a background rejection factor of 5 . 10(7) (1 . 10(7)) at low (high) q(2) for s = 5 GeV2, and of 1 . 10(8) (6 . 10(6)) at low (high) q(2) for s = 10 GeV2, while keeping the signal reconstruction efficiency at around 40%. At both energies, a clean lepton signal can be reconstructed with the expected statistics corresponding to 2 of integrated luminosity. The cross sections obtained from the simulations are used to show that a test of QCD collinear factorization can be done at the lowest order by measuring scaling laws and angular distributions. The future measurement of the signal channel cross section with PANDA will provide a new test of the perturbative QCD description of a novel class of hard exclusive reactions and will open the possibility of experimentally accessing pi N TDAs.
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2.
  • Erni, W., et al. (författare)
  • Technical design report for the PANDA (AntiProton Annihilations at Darmstadt) Straw Tube Tracker
  • 2013
  • Ingår i: European Physical Journal A. Hadrons and Nuclei. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 49:2
  • Tidskriftsartikel (refereegranskat)abstract
    • This document describes the technical layout and the expected performance of the Straw Tube Tracker (STT), the main tracking detector of the PANDA target spectrometer. The STT encloses a Micro-Vertex-Detector (MVD) for the inner tracking and is followed in beam direction by a set of GEM stations. The tasks of the STT are the measurement of the particle momentum from the reconstructed trajectory and the measurement of the specific energy loss for a particle identification. Dedicated simulations with full analysis studies of certain proton-antiproton reactions, identified as being benchmark tests for the whole PANDA scientific program, have been performed to test the STT layout and performance. The results are presented, and the time lines to construct the STT are described.
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3.
  • Alcorn, J, et al. (författare)
  • Basic instrumentation for Hall A at Jefferson Lab
  • 2004
  • Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 522:3, s. 294-346
  • Tidskriftsartikel (refereegranskat)abstract
    • The instrumentation in Hall A at the Thomas Jefferson National Accelerator Facility was designed to study electro-and photo-induced reactions at very high luminosity and good momentum and angular resolution for at least one of the reaction products. The central components of Hall A are two identical high resolution spectrometers, which allow the vertical drift chambers in the focal plane to provide a momentum resolution of better than 2 x 10(-4). A variety of Cherenkov counters, scintillators and lead-glass calorimeters provide excellent particle identification. The facility has been operated successfully at a luminosity well in excess of 10(38) CM-2 s(-1). The research program is aimed at a variety of subjects, including nucleon structure functions, nucleon form factors and properties of the nuclear medium. (C) 2003 Elsevier B.V. All rights reserved.
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4.
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5.
  • Chirapatpimol, K, et al. (författare)
  • Precision Measurement of the p(e,e′p)π0 Reaction at Threshold
  • 2015
  • Ingår i: Physical Review Letters. - 1079-7114. ; 114:19
  • Tidskriftsartikel (refereegranskat)abstract
    • New results are reported from a measurement of π^{0} electroproduction near threshold using the p(e,e^{'}p)π^{0} reaction. The experiment was designed to determine precisely the energy dependence of s- and p-wave electromagnetic multipoles as a stringent test of the predictions of chiral perturbation theory (ChPT). The data were taken with an electron beam energy of 1192 MeV using a two-spectrometer setup in Hall A at Jefferson Lab. For the first time, complete coverage of the ϕ_{π}^{*} and θ_{π}^{*} angles in the pπ^{0} center of mass was obtained for invariant energies above threshold from 0.5 up to 15 MeV. The 4-momentum transfer Q^{2} coverage ranges from 0.05 to 0.155 (GeV/c)^{2} in fine steps. A simple phenomenological analysis of our data shows strong disagreement with p-wave predictions from ChPT for Q^{2}>0.07 (GeV/c)^{2}, while the s-wave predictions are in reasonable agreement.
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6.
  • Puckett, A. J. R., et al. (författare)
  • Final analysis of proton form factor ratio data at Q(2)=4.0, 4.8, and 5.6 GeV2
  • 2012
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 85:4
  • Tidskriftsartikel (refereegranskat)abstract
    • Precise measurements of the proton electromagnetic form factor ratio R = mu(p)G(E)(p)/G(M)(p) using the polarization transfer method at Jefferson Lab have revolutionized the understanding of nucleon structure by revealing the strong decrease of R with momentum transfer Q(2) for Q(2) greater than or similar to 1 GeV2, in strong disagreement with previous extractions of R from cross-section measurements. In particular, the polarization transfer results have exposed the limits of applicability of the one-photon-exchange approximation and highlighted the role of quark orbital angular momentum in the nucleon structure. The GEp-II experiment in Jefferson Lab's Hall A measured R at four Q(2) values in the range 3.5 GeV2 <= Q(2) <= 5.6 GeV2. A possible discrepancy between the originally published GEp-II results and more recent measurements at higher Q(2) motivated a new analysis of the GEp-II data. This article presents the final results of the GEp-II experiment, including details of the new analysis, an expanded description of the apparatus, and an overview of theoretical progress since the original publication. The key result of the final analysis is a systematic increase in the results for R, improving the consistency of the polarization transfer data in the high-Q(2) region. This increase is the result of an improved selection of elastic events which largely removes the systematic effect of the inelastic contamination, underestimated by the original analysis.
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7.
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8.
  • Wijesooriya, K, et al. (författare)
  • Polarization measurements in high-energy deuteron photodisintegration
  • 2001
  • Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 86:14, s. 2975-2979
  • Tidskriftsartikel (refereegranskat)abstract
    • We present measurements of the recoil proton polarization for the d(γ⃗,p⃗)n reaction at θc.m. = 90° for photon energies up to 2.4 GeV. These are the first data in this reaction for polarization transfer with circularly polarized photons. The induced polarization py vanishes above 1 GeV, contrary to meson-baryon model expectations, in which resonances lead to large polarizations. However, the polarization transfer Cx does not vanish above 1 GeV, inconsistent with hadron helicity conservation. Thus, we show that the scaling behavior observed in the d(γ,p)ncross sections is not a result of perturbative QCD. These data should provide important tests of new nonperturbative calculations in the intermediate energy regime.
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9.
  • Dutta, D, et al. (författare)
  • Nuclear transparency with the gamma n ->pi(-)p process in He-4
  • 2003
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 68:2: 021001
  • Tidskriftsartikel (refereegranskat)abstract
    • We have measured the nuclear transparency of the fundamental process gamman-->pi(-)p in He-4. These measurements were performed at Jefferson Lab in the photon energy range of 1.6-4.5 GeV and at theta(cm)(pi)=70degrees and 90degrees. These measurements are the first of their kind in the study of nuclear transparency in photoreactions. They also provide a benchmark test of Glauber calculations based on traditional models of nuclear physics. The transparency results suggest deviations from the traditional nuclear physics picture. The momentum transfer dependence of the measured nuclear transparency is consistent with Glauber calculations that include the quantum chromodynamics phenomenon of color transparency.
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10.
  • Schulte, EC, et al. (författare)
  • High energy angular distribution measurements of the exclusive deuteron photodisintegration reaction
  • 2002
  • Ingår i: Physical Review C (Nuclear Physics). - : American Physical Society. - 0556-2813 .- 1089-490X. ; 66:4
  • Tidskriftsartikel (refereegranskat)abstract
    • The first complete measurements of the angular distributions of the two-body deuteron photodisintegration differential cross section at photon energies above 1.6 GeV were performed at the Thomas Jefferson National Accelerator Facility. The results show a persistent forward-backward asymmetry up to E-gamma=2.4 GeV, the highest-energy measured in this experiment. The Hard Rescattering and the Quark-Gluon string models are in fair agreement with the results.
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11.
  • Strandberg, B., et al. (författare)
  • Compton scattering from the deuteron above pion-production threshold
  • 2018
  • Ingår i: Physical Review C. - 2469-9985. ; 98:1
  • Tidskriftsartikel (refereegranskat)abstract
    • The electromagnetic polarizabilities of the nucleon are fundamental nucleon-structure observables that characterize its response to external electromagnetic fields. The neutron polarizabilities can be accessed from Compton-scattering data on light nuclear targets. Recent measurements of the differential cross section for Compton scattering on the deuteron below the pion-production threshold have decreased the uncertainties in the neutron polarizabilities, yet the proton polarizabilities remain known substantially more accurately. As the sensitivity of the cross section to the polarizabilities increases with incident photon energy, measurements above the pion threshold may offer a way for an improved determination of the neutron polarizabilities. In this Rapid Communiciation, the first measurement of the cross section for coherent Compton scattering on the deuteron above the pion-production threshold is presented.
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12.
  • Strandberg, B., et al. (författare)
  • Near-threshold π-photoproduction on the deuteron
  • 2020
  • Ingår i: Physical Review C. - 2469-9985. ; 101:3
  • Tidskriftsartikel (refereegranskat)abstract
    • The first experimental investigation of the near-threshold cross section for incoherent π-photoproduction on the deuteron γd→π-pp is presented. The experimental technique involved detection of the ≈131 MeV γ ray resulting from the radiative capture of photoproduced π-in the target. The total cross section was measured using an unpolarized tagged-photon beam, a liquid-deuterium target, and three very large NaI(Tl) spectrometers. The data are compared to theoretical models that give insight into the elementary reaction γn→π-p and pion-nucleon and nucleon-nucleon final-state interactions.
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13.
  • Wijesooriya, K, et al. (författare)
  • Polarization measurements in neutral pion photoproduction
  • 2002
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 66:3
  • Tidskriftsartikel (refereegranskat)abstract
    • We present measurements of the recoil proton polarization for the H-1((γ) over right arrow,(p) over right arrow)pi(0) reaction for theta(c.m.)(pi) = 60degrees-135degrees and for photon energies up to 4.1 GeV. These are the first data in this reaction for polarization transfer with circularly polarized photons. Various theoretical models are compared with the results. No evidence for hadron helicity conservation is observed. Models that employ factorization are not favored. It appears from the strong angular dependence of the induced polarization at photon energies of 2.5 and 3.1 GeV that a relatively high spin resonance or background amplitude might exist in this energy region.
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14.
  • Zhu, LY, et al. (författare)
  • Cross-section measurement of charged-pion photoproduction from hydrogen and deuterium
  • 2003
  • Ingår i: Physical Review Letters. - 1079-7114. ; 91:2: 022003
  • Tidskriftsartikel (refereegranskat)abstract
    • We have measured the differential cross section for the gamman-->pi(-)p and gammap-->pi(+)n reactions at theta(c.m.)=90degrees in the photon energy range from 1.1 to 5.5 GeV at Jefferson Lab (JLab). The data at E(gamma)greater than or similar to3.3 GeV exhibit a global scaling behavior for both pi(-) and pi(+) photoproduction, consistent with the constituent counting rule and the existing pi(+) photoproduction data. Possible oscillations around the scaling value are suggested by these new data. The data show enhancement in the scaled cross section at a center-of-mass energy near 2.2 GeV. The cross section ratio of exclusive pi(-) to pi(+) photoproduction at high energy is consistent with the prediction based on one-hard-gluon-exchange diagrams.
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15.
  • Zhu, L Y, et al. (författare)
  • Cross section measurements of charged pion photoproduction in hydrogen and deuterium from 1.1 to 5.5 GeV
  • 2005
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 71:4
  • Tidskriftsartikel (refereegranskat)abstract
    • The differential cross sections for the gamma n ->pi(-)p and the gamma p ->pi(+)n processes were measured at Jefferson Lab. The photon energies ranged from 1.1 to 5.5 GeV, corresponding to center-of-mass energies from 1.7 to 3.4 GeV. The pion center-of-mass angles varied from 50(degrees) to 110(degrees). The pi(-) and pi(+) photoproduction data both exhibit a global scaling behavior at high energies and high transverse momenta, consistent with the constituent counting rule prediction and the existing pi(+) data. The data suggest possible substructure of the scaling behavior, which might be oscillations around the scaling value. The data show an enhancement in the scaled cross section at center-of-mass energy near 2.2 GeV. The differential cross section ratios [d sigma/dt(gamma n ->pi(-)p)/d sigma/dt(gamma p ->pi(+)n)] at high energies and high transverse momenta can be described by calculations based on one-hard-gluon-exchange diagrams.
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16.
  • Boyd, L., et al. (författare)
  • Simulation of the response of the Solid State Neutron Detector for the European Spallation Source
  • 2021
  • Ingår i: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002. ; 998
  • Tidskriftsartikel (refereegranskat)abstract
    • The characteristics of the Solid-state Neutron Detector, under development for neutron-scattering measurements at the European Spallation Source, have been simulated with a Geant4-based computer code. The code models the interactions of thermal neutrons and ionising radiation in the 6Li-doped scintillating glass of the detector, the production of scintillation light and the transport of optical, scintillation photons through the scintillator, en route to the photocathode of the attached multi-anode photomultiplier. Factors which affect the optical-photon transport, such as surface finish, pixelation of the glass sheet, provision of a front reflector and optical coupling media are compared. Predictions of the detector response are compared with measurements made with neutron and gamma-ray sources, a collimated alpha source and finely collimated beams of 2.5 MeV protons and deuterons.
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17.
  • Brudvik, G., et al. (författare)
  • Measurement of d(γ,p) reaction cross sections and asymmetry with linearly polarized coherent bremsstrahlung beam
  • 2018
  • Ingår i: Problems of Atomic Science and Technology. - 1682-9344. ; 115:3, s. 132-139
  • Tidskriftsartikel (refereegranskat)abstract
    • On the base of reaction of deuteron photo-disintegration it was studied possibility of the simultaneous measuring of cross sections and asymmetry of the (γ,p) reactions at the using of the coherent polarized photon beam. Measurements were performed for the proton emission angle 90°. The cross sections well agree with the literary data, obtained on the bremsstrahlung photon beam in the range of energies 45…80 MeV.
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18.
  • Brudvik, Jason, et al. (författare)
  • Improvement of energy resolution of ΔE-E CsI/SSD- telescope at measurement of (γ,p)-Reactions using strip information of SSD
  • 2016
  • Ingår i: Problems of Atomic Science and Technology. - 1682-9344. ; 103:3, s. 111-115
  • Tidskriftsartikel (refereegranskat)abstract
    • Information on the triggered strips of silicon strip detectors of a MAX-lab ΔE-E CsI/SSD-telescope was used to determination the angular range of emitted reaction particles. It allowed an improvement in the energy resolution of the telescope by decreasing the kinematical broadening of the missing energy spectra of12C(γ,p)11B reaction, and enabling more accurate separation of exited states of residual nucleus.
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19.
  • Burdeinyi, D., et al. (författare)
  • Cross section asymmetry of two-body carbon disintegration 12C(γ,p)11B with polarized photons at energy 40–50 MeV
  • 2017
  • Ingår i: Nuclear Physics A. - : Elsevier BV. - 0375-9474. ; 957, s. 321-331
  • Tidskriftsartikel (refereegranskat)abstract
    • The cross section asymmetry of C12(γ,p01)B11 and C12(γ,p2−6)B11 reactions has been studied at the energy range 40–55 MeV, using linearly polarized tagged photons of the MAX-lab facility. The asymmetry of the C12(γ,p01)B11 processes, which assume the one-body mechanism of the reaction, is Σ≈0.82±0.05 for photon energies 45–50 MeV. The asymmetry for the C12(γ,p2−6)B11 reactions, which produce a maximum at excitation energy ∼6 MeV, is Σ≈0.53±0.13 for a photon energy 49 MeV. It is close to the asymmetry of reaction of the free deuteron photodisintegration, and can be resulted from the two-body mechanism of the photon absorption.
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20.
  • Burdeinyi, D. D., et al. (författare)
  • Cross section asymmetry of the 12C(γ; p0)11B and 12C(γ; p1)11B reactions at photon energies 40...55 MeV
  • 2019
  • Ingår i: Problems of Atomic Science and Technology. - 1682-9344. ; 121:3, s. 26-37
  • Tidskriftsartikel (refereegranskat)abstract
    • The asymmetry of the cross section of the 12C(γ; p0)11B and 12C(γ; p1)11B reactions has been measured in the energy range 40...55MeV using linearly polarized tagged photons of the MAX-lab facility. The asymmetry of the process 12C(γ; p0)11B is Σ ∼ 0:85, that implies one-particle reaction mechanism. The asymmetry of the reaction 12C(γ; p1)11B is smaller, Σ ∼ 0.6...0.7, that may be due to the stronger relative contribution of the 2h − 1p mechanism to the dominant one-particle reaction mechanism.
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21.
  • Burdeinyi, D. D., et al. (författare)
  • Study of C12(γ→,p)11B reactions with polarized photons at energy 40-65 MeV
  • 2024
  • Ingår i: Nuclear Physics A. - 0375-9474. ; 1048
  • Tidskriftsartikel (refereegranskat)abstract
    • The photon beam asymmetry of the C12(γ→,p01)11B and C12(γ→,p2−6)11B reactions has been measured in the energy range 40–65 MeV, using a tagged, linearly-polarized photon beam at the MAX-lab facility in Sweden. The asymmetry of the C12(γ→,p01)11B reaction to ground and first excited state of B11 is Σ≈0.82 over the measured energy range. The main contribution to the C12(γ→,p2−6)11B reaction to higher excited states comes from processes in which the residual nucleus is in the 3/2−(5.02 MeV) or 7/2−(6.74 MeV) excited states. The asymmetry of this reaction is Σ≈0.6, close to the value for free deuteron photodisintegration.
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22.
  • Burdeinyi, D., et al. (författare)
  • Measurement of (γ, p) reactions with ΔE - E telescope at MAX-lab facility
  • 2015
  • Ingår i: Problems of Atomic Science and Technology. - 1682-9344. ; 97:3, s. 49-64
  • Tidskriftsartikel (refereegranskat)abstract
    • The paper considers the results of experiments on the reactions 12C(γ, p)11B and d(γ, p)n in the energy range of tagged photons 35...80 MeV. Demonstrated the possibility identification of protons by ΔE - E using CsI/SSD telescope. Using the spectra of the missing energy defined the values of differential cross sections of these reactions in the range of photon energies. The good agreement of the experimental results with the available data in the literature.
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23.
  • Feldman, G., et al. (författare)
  • New results for Compton scattering on deuterium : A better determination of the neutron electromagnetic polarizabilities
  • 2015
  • Ingår i: Proceedings of Science. - 1824-8039.
  • Tidskriftsartikel (refereegranskat)abstract
    • The electric and magnetic polarizabilities of the proton are now well known, owing to Compton scattering measurements on hydrogen targets; however, the neutron polarizabilities are still relatively uncertain, compared to the proton values. To address this problem, a multiinstitutional collaboration has conducted a program of elastic Compton scattering experiments on deuterium at the MAX IV Laboratory in Lund, Sweden using tagged photons in the energy range Eγ= 65-115 MeV. We assembled at one laboratory, for the first time, three of the world's largest NaI detectors, each having better than ΔE/E ∼ 2% photon energy resolution. We have measured elastic Compton scattering cross sections at lab angles of θγ= 60°, 120° and 150° over this energy range in 8 MeV steps. This effectively doubles the world's set of elastic Compton scattering data from deuterium and provides valuable input for chiral effective field theory (χEFT) calculations. These new deuterium data overlap previous measurements and extend them by 20 MeV to higher energies. Based on χEFT fits to the expanded world data set, new values for the neutron electric and magnetic polarizabilities have been obtained with greater accuracy than previously achieved, decreasing the statistical error by more than 30%.
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24.
  • Fissum, K., et al. (författare)
  • Radiation Spectra of 200 MeV Electrons in Diamond and Silicon Crystals at Axial and Planar Orientations
  • 2010
  • Ingår i: Charged and Neutral Particles Channeling Phenomena : Proceedings of the 51st Workshop of the INFN ELOISATRON Project , Erice, Italy , 25 October – 1 November 2008 - Proceedings of the 51st Workshop of the INFN ELOISATRON Project , Erice, Italy , 25 October – 1 November 2008. - : WORLD SCIENTIFIC. ; , s. 331-334
  • Konferensbidrag (refereegranskat)abstract
    • Results of the first experiment on studying the radiation spectra of electrons with energy 192 7 MeV in diamond and silicon crystals at axial and plane orientation performed at the MAX-lab facility were presented. At these orientation the particle's motion can be both regular, when axial and planar channeling are possible, and chaotic, when the coherent electron interaction with single strings reveals itself. Essential increase of the radiation intensity at low photon energy region, less than 15 MeV, is observed.
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25.
  • Ganenko, V. B., et al. (författare)
  • Mechanisms of 200 MeV electron radiation in diamond crystal in the axial orientation
  • 2018
  • Ingår i: Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms. - : Elsevier BV. - 0168-583X. ; 424, s. 17-25
  • Tidskriftsartikel (refereegranskat)abstract
    • The γ-radiation by electrons with the energy of ∼200 MeV in a 100μm-thick diamond crystal has been measured at the MAX-lab experimental facility, when the electrons are incident on the crystal along the 〈100〉 axis. In this case, the intensity of the -radiation with the energy ∼1–2 MeV is approximately 16 times higher than that in amorphous matter of the same thickness. Theoretical calculations based on the quasi-classical QED approximation are in good agreement with the experimental data. The analysis of the radiation mechanisms has shown that the main contribution to the radiation intensity resulted from electrons, moving in the above-barrier regime and at small angles to the crystal axis.
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26.
  • Kelly, J. J., et al. (författare)
  • Recoil polarization measurements for neutral pion electroproduction at Q(2)=1(GeV/c)(2) near the Delta resonance
  • 2007
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 75:2
  • Tidskriftsartikel (refereegranskat)abstract
    • We measured angular distributions of differential cross section, beam analyzing power, and recoil polarization for neutral pion electroproduction at Q(2)=1.0 (GeV/c)(2) in 10 bins of 1.17 <= W <= 1.35 GeV across the Delta resonance. A total of 16 independent response functions were extracted, of which 12 were observed for the first time. Comparisons with recent model calculations show that response functions governed by real parts of interference products are determined relatively well near the physical mass, W=M-Delta approximate to 1.232 GeV, but the variation among models is large for response functions governed by imaginary parts, and for both types of response functions, the variation increases rapidly with W > M-Delta. We performed a multipole analysis that adjusts suitable subsets of center dot(pi)<= 2 amplitudes with higher partial waves constrained by baseline models. This analysis provides both real and imaginary parts. The fitted multipole amplitudes are nearly model independent-there is very little sensitivity to the choice of baseline model or truncation scheme. By contrast, truncation errors in the traditional Legendre analysis of N ->Delta quadrupole ratios are not negligible. Parabolic fits to the W dependence around M-Delta for the multiple analysis gives values for Re(S1+/M1+)=(-6.61 +/- 0.18)% and Re(E1+/M1+)=(-2.87 +/- 0.19)% for the p pi(0) channel at W=1.232 GeV and Q(2)=1.0 (GeV/c)(2) that are distinctly larger than those from the Legendre analysis of the same data. Similarly, the multipole analysis gives Re(S0+/M1+)=(+7.1 +/- 0.8)% at W=1.232 GeV, consistent with recent models, while the traditional Legendre analysis gives the opposite sign because its truncation errors are quite severe.
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27.
  • Myers, L. S., et al. (författare)
  • Compton scattering from C-12 using tagged photons in the energy range 65-115 MeV
  • 2014
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 89:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Elastic scattering of photons from C-12 has been investigated using quasimonoenergetic tagged photons with energies in the range 65-115 MeV at laboratory angles of 60 degrees, 120 degrees, and 150 degrees. at the Tagged-Photon Facility at the MAX IV Laboratory in Lund, Sweden. A phenomenological model was employed to provide an estimate of the sensitivity of the C-12(gamma,gamma)C-12 cross section to the bound- nucleon polarizabilities.
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28.
  • Rofors, E., et al. (författare)
  • Response of a Li-glass/multi-anode photomultiplier detector to focused proton and deuteron beams
  • 2020
  • Ingår i: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002. ; 984
  • Tidskriftsartikel (refereegranskat)abstract
    • The response of a position-sensitive Li-glass based scintillation detector being developed for thermal-neutron detection with 6 mm position resolution has been investigated using focused beams of 2.5MeV protons and deuterons. The beams were scanned across the detector in 0.5 mm horizontal and vertical steps perpendicular to the beams. Scintillation light was registered using an 8 × 8 pixel multi-anode photomultiplier tube. The signal amplitudes were recorded for each pixel on an event-by-event basis. Several pixels generally registered considerable signals at each beam location. To optimize planned detector operation at the European Spallation Source, the number of pixels above set thresholds was investigated, with the maximization of the single-hit efficiency over the largest possible area as the primary goal. For both beams, at a threshold of ∼50% of the mean of the full-deposition peak, ∼80% of the events were registered in a single pixel, resulting in an effective position resolution of ∼5 mm in X and Y. Lower thresholds resulted in higher pixel multiplicities. These events could also be localized with the same effective position resolution.
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29.
  • Adler, Jan-Olof, et al. (författare)
  • The upgraded photon tagging facility at the MAX IV Laboratory
  • 2013
  • Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 715, s. 1-10
  • Tidskriftsartikel (refereegranskat)abstract
    • A description is given of the upgraded photon tagging facility at the MAX IV Laboratory. Two magnetic spectrometers are used to momentum analyze post-bremsstrahlung electrons. The tagged photon range extends from 10 to 180 MeV with an energy resolution of about 300 keV. The system has been operated at rates up to 4 x 10(6) photons s(-1) MeV (-1). Different diagnostic tools are described as well as the experimental program.
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30.
  • Frost, R. J. W., et al. (författare)
  • A compact accelerator driven neutron source at the Applied Nuclear Physics Laboratory, Lund University
  • 2023
  • Ingår i: EPJ TECHNIQUES AND INSTRUMENTATION. - : Springer Nature. - 2195-7045. ; 10:1
  • Tidskriftsartikel (refereegranskat)abstract
    • The Applied Nuclear Physics Group at Lund University has constructed a CANS (Compact Accelerator-driven Neutron Source). The CANS is based around a 3 MV, single-ended, Pelletron accelerator, which is used to impinge a 2.8 MeV deuterium beam into a beryllium target. The anticipated neutron production will be on the order of 10(10) n/s in 4 pi sr, with future upgrades expected to increase neutron production to 10(11) n/s. Neutron energy will be up to 9 MeV with peak emission at similar to 5 MeV. Shielding and moderation will be provided by a large water tank surrounding the target, with exit ports to allow moderated neutrons to be directed to experiments. The thermal-neutron flux at the exit of the extraction ports is anticipated to be up to 10(6) n/cm(2)/s. The CANS will be used to forward the activities of the group in the area of neutron-activation analysis, in addition to a broader range of neutron related applications.
  •  
31.
  • Gayou, O, et al. (författare)
  • Measurement of G(Ep)/G(Mp) in (e)over-right-arrowp -> e(p)over-right-arrow to Q(2)=5.6 GeV2
  • 2002
  • Ingår i: Physical Review Letters. - 1079-7114. ; 88:9
  • Tidskriftsartikel (refereegranskat)abstract
    • The ratio of the electric and magnetic form factors of the proton G(Ep)/G(Mp), which is an image of its charge and magnetization distributions, was measured at the Thomas Jefferson National Accelerator Facility (JLab) using the recoil polarization technique. The ratio of the form factors is directly proportional to the ratio of the transverse to longitudinal components of the polarization of the recoil proton in the elastic (e) over right arrowp --> e (p) over right arrow reaction. The new data presented span the range 3.5 < Q(2) < 5.6 GeV2 and are well described by a linear Q(2) fit. Also, the ratio rootQ(2) F-2p/F-1p reaches a constant value above Q(2) = 2 GeV2.
  •  
32.
  •  
33.
  • Maulerova, V., et al. (författare)
  • Vanadium-based neutron beam monitor
  • 2020
  • Ingår i: Physical Review Accelerators and Beams. - 2469-9888. ; 23:7
  • Tidskriftsartikel (refereegranskat)abstract
    • A prototype quasiparasitic thermal neutron beam monitor based on isotropic neutron scattering from a thin natural vanadium foil and standard He3 proportional counters is conceptualized, designed, simulated, calibrated, and commissioned. The European Spallation Source designed to deliver the highest integrated neutron flux originating from a pulsed source is currently under construction in Lund, Sweden. The effort to investigate a vanadium-based neutron beam monitor was triggered by a list of requirements for beam monitors permanently placed in the ESS neutron beams in order to provide reliable monitoring at complex beam lines: low attenuation, linear response over a wide range of neutron fluxes, near to constant efficiency for neutron wavelengths in a range of 0.6-10 Å, calibration stability and the possibility to place the system in vacuum are all desirable characteristics. The scattering-based prototype, employing a natural vanadium foil and standard He3 proportional counters, was investigated at the V17 and V20 neutron beam lines of the Helmholtz-Zentrum in Berlin, Germany, in several different geometrical configurations of the He3 proportional counters around the foil. Response linearity is successfully demonstrated for foil thicknesses ranging from 0.04 mm to 3.15 mm. Attenuation lower than 1% for thermal neutrons is demonstrated for the 0.04 mm and 0.125 mm foils. The geometries used for the experiment were simulated allowing for absolute flux calibration and establishing the possible range of efficiencies for various designs of the prototype. The operational flux limits for the beam monitor prototype were established as a dependency of the background radiation and prototype geometry. The herein demonstrated prototype monitors can be employed for neutron intensities ranging from 103-1010 n/s.
  •  
34.
  • Mauritzson, N., et al. (författare)
  • Light-yield response of liquid scintillators using 2-6 MeV tagged neutrons
  • 2024
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier. - 0168-9002 .- 1872-9576. ; 1062
  • Tidskriftsartikel (refereegranskat)abstract
    • Knowledge of the neutron light -yield response is crucial to the understanding of scintillator-based neutron detectors. In this work, neutrons from 2-6 MeV have been used to study the scintillation light -yield response of the liquid scintillators NE 213A, EJ 305, EJ 331 and EJ 321P using event -by -event waveform digitization. Energy calibration was performed using a GEANT4 model to locate the edge positions of the Compton distributions produced by gamma -ray sources. The simulated light yield for neutrons from a PuBe source was compared to measured recoil proton distributions, where neutron energy was selected by time -of -flight. This resulted in an energy -dependent Birks parameterization to characterize the non-linear response to the lower energy neutrons. The NE 213A and EJ 305 results agree very well with existing data and are reproduced nicely by the simulation. New results for EJ 331 and EJ 321P, where the simulation also reproduces the data well, are presented.
  •  
35.
  • Mauritzson, N., et al. (författare)
  • Light-yield response of liquid scintillators using 2–6 MeV tagged neutrons
  • 2024
  • Ingår i: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - 0168-9002. ; 1062
  • Tidskriftsartikel (refereegranskat)abstract
    • Knowledge of the neutron light-yield response is crucial to the understanding of scintillator-based neutron detectors. In this work, neutrons from 2–6 MeV have been used to study the scintillation light-yield response of the liquid scintillators NE 213A, EJ 305, EJ 331 and EJ 321P using event-by-event waveform digitization. Energy calibration was performed using a GEANT4 model to locate the edge positions of the Compton distributions produced by gamma-ray sources. The simulated light yield for neutrons from a PuBe source was compared to measured recoil proton distributions, where neutron energy was selected by time-of-flight. This resulted in an energy-dependent Birks parameterization to characterize the non-linear response to the lower energy neutrons. The NE 213A and EJ 305 results agree very well with existing data and are reproduced nicely by the simulation. New results for EJ 331 and EJ 321P, where the simulation also reproduces the data well, are presented.
  •  
36.
  • Mauritzson, N., et al. (författare)
  • Technique for the measurement of intrinsic pulse-shape discrimination for organic scintillators using tagged neutrons
  • 2022
  • Ingår i: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002. ; 1039
  • Tidskriftsartikel (refereegranskat)abstract
    • Fast-neutron/gamma-ray pulse-shape discrimination has been performed for the organic liquid scintillators NE 213A and EJ 305 using a time-of-flight based neutron-tagging technique and waveform digitization on an event-by-event basis. Gamma-ray sources and a Geant4-based simulation were used to calibrate the scintillation-light yield. The difference in pulse shape for the neutron and gamma-ray events was analyzed by integrating selected portions of the digitized waveform to produce a figure-of-merit for neutron/gamma-ray separation. This figure-of-merit has been mapped as a function of detector threshold and also of neutron energy determined from time-of-flight. It shows clearly that the well-established pulse-shape discrimination capabilities of NE 213A are superior to those of EJ 305. The extra information provided by the neutron-tagging technique has resulted in a far more detailed assessment of the pulse-shape-discrimination capabilities of these organic scintillators.
  •  
37.
  • Messi, F., et al. (författare)
  • Gamma- and Fast Neutron- Sensitivity of 10B- Based Neutron Detectors at ESS
  • 2017
  • Ingår i: 2017 IEEE Nuclear Science Symposium and Medical Imaging Conference, NSS/MIC 2017 - Conference Proceedings. - 9781538622827
  • Konferensbidrag (refereegranskat)abstract
    • The European Spallation Source (ESS), presently under construction in Lund, Sweden, is designed to be the world's brightest neutron source. When it will be in operation, ESS will deliver an instantaneous neutron flux on detectors that will be without precedent. A down side of the high brightness will be the increase of background, especially from gamma-rays and fast-neutrons.Considering that scattering cross-sections of many samples tend to be relatively low and that the gamma- and fast-neutronbackgrounds tend to be considerable high at spallation facilities [Che +14], the signal-to-noise ratio of a measurement needs to be maximised. The sensitivity of a thermal-neutron detector to gamma-rays and to fast-neutrons is a very important characteristic, as it defines the best achievable signal-to-noise ratio for the measurement. It is therefore crucial to measure the gamma- and fast-neutron- sensitivities of all detectors that will be installed on the instruments at ESS.
  •  
38.
  • Messi, F., et al. (författare)
  • The neutron-tagging facility at Lund University
  • 2020
  • Ingår i: Modern Neutron Detection : Proceedings of a Technical Meeting - Proceedings of a Technical Meeting. - 1011-4289. - 9789201265203 - 9789201266200 ; :1935, s. 287-297
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Over the last decades, the field of thermal neutron detection has overwhelmingly employed He-3-based technologies. The He-3 crisis together with the forthcoming establishment of the European Spallation Source have necessitated the development of new technologies for neutron detection. Today, several promising He-3-free candidates are under detailed study and need to be validated. This validation process is in general long and expensive. The study of detector prototypes using neutron-emitting radioactive sources is a cost-effective solution, especially for preliminary investigations. That said, neutron-emitting sources have the general disadvantage of broad, structured, emitted-neutron energy ranges. Further, the emitted neutrons often compete with unwanted backgrounds of gamma-rays, alpha-particles, and fission-fragments. By blending experimental infrastructure such as shielding to provide particle beams with neutron-detection techniques such as tagging, disadvantages may be converted into advantages. In particular, a technique known as tagging involves exploiting the mixed-field generally associated with a neutron-emitting source to determine neutron time-of-flight and thus energy on an event-by-event basis. This allows for the definition of low-cost, precision neutron beams. The Source-Testing Facility, located at Lund University in Sweden and operated by the SONNIG Group of the Division of Nuclear Physics, was developed for just such low-cost studies. Precision tagged-neutron beams derived from radioactive sources are available around-the-clock for advanced detector diagnostic studies. Neutron measurements performed at the Source Testing Facility are thus cost-effective and have a very low barrier for entry. In this paper, we present an overview of the project.
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39.
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40.
  • Rofors, E., et al. (författare)
  • Response of a Li-glass/multi-anode photomultiplier detector to alpha-particles from Am-241
  • 2019
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 929, s. 90-96
  • Tidskriftsartikel (refereegranskat)abstract
    • The response of a position-sensitive Li-glass scintillator detector to alpha-particles from a collimated Am-241 source scanned across the face of the detector has been measured. Scintillation light was read out by an 8 x 8 pixel multi-anode photomultiplier and the signal amplitude for each pixel has been recorded for every position on a scan. The pixel signal is strongly dependent on position and in general several pixels will register a signal (a hit) above a given threshold. The effect of this threshold on hit multiplicity is studied, with a view to optimize the single-hit efficiency of the detector.
  •  
41.
  • Rofors, E., et al. (författare)
  • Response of a Li-glass/multi-anode photomultiplier detector to collimated thermal-neutron beams
  • 2021
  • Ingår i: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002. ; 999
  • Tidskriftsartikel (refereegranskat)abstract
    • The response of a position-sensitive Li-glass scintillator detector being developed for thermal-neutron detection with 6 mm position resolution has been investigated using collimated beams of thermal neutrons. The detector was moved perpendicularly through the neutron beams in 0.5 to 1.0 mm horizontal and vertical steps. Scintillation was detected in an 8 × 8 pixel multi-anode photomultiplier tube on an event-by-event basis. In general, several pixels registered large signals at each neutron-beam location. The number of pixels registering signal above a set threshold was investigated, with the maximization of the single-hit efficiency over the largest possible area of the detector as the primary goal. At a threshold of ∼50% of the mean of the full-deposition peak, ∼80% of the events were registered in a single pixel, resulting in an effective position resolution of ∼5 mm in X and Y. Lower thresholds generally resulted in events demonstrating higher pixel multiplicities, but these events could also be localized with ∼5 mm position resolution.
  •  
42.
  • Rofors, E., et al. (författare)
  • Response of a Li-glass/multi-anode photomultiplier detector to α-particles from 241 Am
  • 2019
  • Ingår i: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002. ; 929, s. 90-96
  • Tidskriftsartikel (refereegranskat)abstract
    • The response of a position-sensitive Li-glass scintillator detector to α-particles from a collimated 241 Am source scanned across the face of the detector has been measured. Scintillation light was read out by an 8 × 8 pixel multi-anode photomultiplier and the signal amplitude for each pixel has been recorded for every position on a scan. The pixel signal is strongly dependent on position and in general several pixels will register a signal (a hit) above a given threshold. The effect of this threshold on hit multiplicity is studied, with a view to optimize the single-hit efficiency of the detector.
  •  
43.
  • Scherzinger, J., et al. (författare)
  • Tagging fast neutrons from an 241Am/9Be source
  • 2015
  • Ingår i: Applied Radiation and Isotopes. - : Elsevier BV. - 0969-8043 .- 1872-9800. ; 98, s. 74-79
  • Tidskriftsartikel (refereegranskat)abstract
    • Shielding, coincidence, and time-of-flight measurement techniques are employed to tag fast neutrons emitted from an 241Am/9Be source resulting in a continuous polychromatic energy-tagged beam of neutrons with energies up to 7MeV. The measured energy structure of the beam agrees qualitatively with both previous measurements and theoretical calculations.
  •  
44.
  • Scherzinger, J., et al. (författare)
  • The light-yield response of a NE-213 liquid-scintillator detector measured using 2–6 MeV tagged neutrons
  • 2016
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 840, s. 121-127
  • Tidskriftsartikel (refereegranskat)abstract
    • The response of a NE-213 liquid-scintillator detector has been measured using tagged neutrons from 2 to 6 MeV originating from an Am/Be neutron source. The neutron energies were determined using the time-of-flight technique. Pulse-shape discrimination was employed to discern between gamma-rays and neutrons. The behavior of both the fast (35 ns) and the combined fast and slow (475 ns) components of the neutron scintillation-light pulses were studied. Three different prescriptions were used to relate the neutron maximum energy-transfer edges to the corresponding recoil-proton scintillation-light yields, and the results were compared to simulations. The overall normalizations of parametrizations which predict the fast or total light yield of the scintillation pulses were also tested. Our results agree with both existing data and existing parametrizations. We observe a clear sensitivity to the portion and length of the neutron scintillation-light pulse considered.
  •  
45.
  • Strandberg, B., et al. (författare)
  • Threshold π - production on the deuteron
  • 2016
  • Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 130
  • Tidskriftsartikel (refereegranskat)abstract
    • An experiment that aims to measure the π- photoproduction cross-section σ(E) on the deuteron γ + 2H → π- + 2p near threshold is discussed. The main concepts of the experimental technique are presented alongside some preliminary signals.
  •  
46.
  • Strauch, S, et al. (författare)
  • Polarization transfer in the He-4((e)over-right-arrow,e '(p)over-right-arrow)H-3 reaction up to Q(2)=2.6 (GeV/c)(2)
  • 2003
  • Ingår i: Physical Review Letters. - 1079-7114. ; 91:5: 052301
  • Tidskriftsartikel (refereegranskat)abstract
    • We have measured the proton recoil polarization in the He-4((e) over right arrow ,e(')(p) over right arrow)H-4 reaction at Q(2)=0.5, 1.0, 1.6, and 2.6 (GeV/c)(2). The measured ratio of polarization transfer coefficients differs from a fully relativistic calculation, favoring the inclusion of a medium modification of the proton form factors predicted by a quark-meson coupling model. In addition, the measured induced polarizations agree reasonably well with the fully relativistic calculation indicating that the treatment of final-state interactions is under control.
  •  
47.
  • Aniol, K. A., et al. (författare)
  • Measurement of the neutral weak form factors of the proton
  • 1999
  • Ingår i: Physical Review Letters. - 1079-7114. ; 82:6, s. 1096-1100
  • Tidskriftsartikel (refereegranskat)abstract
    • We have measured the parity-violating electroweak asymmetry in the elastic scattering of polarized electrons from the proton. The kinematic point [ ⟨θlab⟩=12.3° and ⟨Q2⟩=0.48(GeV/c)2] is chosen to provide sensitivity, at a level that is of theoretical interest, to the strange electric form factor GsE. The result, A=−14.5±2.2ppm, is consistent with the electroweak standard model and no additional contributions from strange quarks. In particular, the measurement implies GsE+0.39GsM=0.023±0.034(stat)±0.022(syst)±0.026(δGnE), where the last uncertainty arises from the estimated uncertainty in the neutron electric form factor.
  •  
48.
  •  
49.
  • DiJulio, D. D., et al. (författare)
  • A polyethylene-B4C based concrete for enhanced neutron shielding at neutron research facilities
  • 2017
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 859, s. 41-46
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the development of a specialized concrete for neutron shielding at neutron research facilities, based on the addition of hydrogen atoms in the form of polyethylene and also B4C for enhancing the neutron capture properties of the concrete. We show information on the mechanical properties of the concrete and the neutronics, in particular its relevance to modern spallation neutron sources, such as the European Spallation Source (ESS), currently under construction in Lund, Sweden. The new concrete exhibits a 15% lower mass density, a compressible strength of 50% relative to a standard concrete and a significant increase in performance of shielding against MeV neutrons and lower energies. The concrete could find application at the ESS in for example common shielding components, individual beamline shielding and instrument caves. Initial neutronic tests of the concrete, carried out at Lund University, have also verified the performance in the MeV neutron energy range and the results are presented.
  •  
50.
  • Fissum, Kevin, et al. (författare)
  • The Coherent Bremsstrahlung Beam at MAX-lab Facility
  • 2008
  • Ingår i: Charged and Neutral Particles Channeling Phenomena Channeling 2008 : Proceedings of the 51st Workshop of the INFN ELOISATRON Project - Proceedings of the 51st Workshop of the INFN ELOISATRON Project. - : WORLD SCIENTIFIC. ; , s. 49-61
  • Konferensbidrag (refereegranskat)abstract
    • The linearly polarized photon beam for photonuclear researches has been produced at MAX-lab facility on the base of coherent bremsstrahlung process of electrons in a diamond crystal. Test experiments have been performed at electron energies 143.9 and 192.7 MeV with a diamond crystal 0.1 mm thick. The measured coherent bremsstrahlung spectra demonstrate typical features to be observed at higher electron energies. The polarization ~35% was obtained at coherent peak energy of ~60 MeV. The experiments have shown that produced polarized photon beam can be used for photonuclear investigations at energy range up to 60 MeV. To extend the energy range it is necessary to increase maximal energy of the electron beam up to 250 MeV.
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