| 1. |
- Kirstein, Oliver, et al.
(författare)
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Neutron position sensitive detectors for the ESS
- 2014
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Ingår i: Proceedings of Science. - : Proceedings of Science (PoS). ; Vertex2014, s. 029-029
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Konferensbidrag (refereegranskat)abstract
- The European Spallation Source (ESS) in Lund, Sweden will become the world's leading neutron source for the study of materials. It will be a long pulse source, with an average beam power of 5 MW delivered to the target station. The ESS is in the construction phase, which started in 2013 with the completion of the Technical Design Report (TDR). The instruments are being selected from conceptual proposals submitted by groups from around Europe. These instruments present numerous challenges for detector technology in the absence of the availability of Helium-3, which is the default choice for detectors for instruments built until today and due to the extreme rates expected across the ESS instrument suite. Additionally a new generation of source requires a new generation of detector technologies to fully exploit the opportunities that this source provides. To meet this challenge at a green-field site, the detectors will be sourced from partners across Europe through numerous in-kind arrangements; a process that is somewhat novel for the neutron scattering community. This contribution presents briefly the current status of detectors for the ESS, and outlines the timeline to completion. For a conjectured instrument suite based upon instruments recommended for construction, a recently updated snapshot of the current expected detector requirements is presented. A strategy outline as to how these requirements might be tackled by novel detector developments is shown. In terms of future developments for the neutron community, synergies should be sought with other disciples, as recognized by various recent initiatives in Europe, in the context of the fundamentally multi-disciplinary nature of detectors. This strategy has at its basis the in-kind and collaborative partnerships necessary to be able to produce optimally performant detectors that allow the ESS instruments to be world-leading. This foresees and encourages a high level of collaboration and interdependence at its core, and rather than each group being all-rounders in every technology, the further development of centres of excellence across Europe for particular technologies and niches.
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| 2. |
- Adler, Jan-Olof, et al.
(författare)
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A broad range tagging spectrometer for the MAX-laboratory
- 1997
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - 0167-5087. ; 388:1-2, s. 17-26
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Tidskriftsartikel (refereegranskat)abstract
- A broad range tagging spectrometer together with a new beam transport system for photonuclear experiments at the MAX-laboratory in Lund is described. The spectrometer consists of a quadrupole followed by an Elbek-type dipole and has a large momentum acceptance. It can produce both polarized and unpolarized tagged photons in the energy range 10–80 MeV with an energy resolution of about 300 keV.
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| 3. |
- Adler, Jan-Olof, et al.
(författare)
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The upgraded photon tagging facility at the MAX IV Laboratory
- 2013
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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
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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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| 4. |
- Al Jebali, Ramsey, et al.
(författare)
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A helium gas scintillator active target for photoreaction measurements
- 2015
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Ingår i: European Physical Journal A. Hadrons and Nuclei. - : Springer Science and Business Media LLC. - 1434-6001. ; 51:10
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Tidskriftsartikel (refereegranskat)abstract
- A multi-cell He gas scintillator active target, designed for the measurement of photoreaction cross sections, is described. The target has four main chambers, giving an overall thickness of 0.103 g/cm(3) at an operating pressure of 2MPa. Scintillations are read out by photomultiplier tubes and the addition of small amounts of N-2 to the He, to shift the scintillation emission from UV to visible, is discussed. First results of measurements at the MAX IV Laboratory tagged-photon facility show that the target has a timing resolution of around 1 ns and can cope well with a high-flux photon beam. The determination of reaction cross sections from target yields relies on a Monte Carlo simulation, which considers scintillation light transport, photodisintegration processes in He-4, background photon interactions in target windows and interactions of the reaction-product particles in the gas and target container. The predictions of this simulation are compared to the measured target response.
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| 5. |
- Al Jebali, Ramsey, et al.
(författare)
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Recent Developments SoNDe High-Flux Detector Project
- 2018
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Ingår i: Recent Developments SoNDe High-Flux Detector Project.
-
Konferensbidrag (refereegranskat)abstract
- New high-flux and high-brilliance neutron sources demand a higher count-rate capability in neutron detectors. In order to achieve that goal, the Solid-State Neutron Detector (SoNDe) project is developing a scintillation-based neutron detector. It will be capable of fully exploiting the available flux at small-angle neutron scattering (SANS) instruments at high brilliance sources, such as SKADI at the European Spallation Source (ESS). The read-out of the scintillator is based on a pixelized multi-anode PMT (MaPMT), where each pixel is treated separately. In addition to enabling higher achievable count-rates, one of the design goals was to develop a modular and scalable solution that can also be used in other instruments or even contexts, such as for laboratory setups. This has been achieved by combining the complete read-out electronics along with the MaPMT into modules that can be controlled and read-out individually via a network without additional any infrastructure. An overview of the present state of development and current test results is presented, highlighting the results of previously published project reports.
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| 6. |
- Alcorn, J, et al.
(författare)
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Basic instrumentation for Hall A at Jefferson Lab
- 2004
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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
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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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| 7. |
- Alexa, L. C., et al.
(författare)
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Measurements of the Deuteron Elastic Structure Function A(Q2) for 0.7≤Q2≤6.0(GeV/c)2 at Jefferson Laboratory
- 1999
-
Ingår i: Physical Review Letters. - 1079-7114. ; 82:7, s. 1374-1378
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Tidskriftsartikel (refereegranskat)abstract
- The deuteron elastic structure function A(Q2) has been extracted in the range 0.7≤Q2≤6.0(GeV/c)2 from cross section measurements of elastic electron-deuteron scattering in coincidence using the Hall A Facility of Jefferson Laboratory. The data are compared to theoretical models, based on the impulse approximation with the inclusion of meson-exchange currents, and to predictions of quark dimensional scaling and perturbative quantum chromodynamics.
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| 8. |
- Amarian, M, et al.
(författare)
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Measurement of the Generalized Forward Spin Polarizabilities of the Neutron
- 2004
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Ingår i: Physical Review Letters. - 1079-7114. ; 93
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Tidskriftsartikel (refereegranskat)abstract
- The generalized forward spin polarizabilities 0 and LT of the neutron have been extracted for the first time in a Q2 range from 0.1 to 0.9 GeV2. Since 0 is sensitive to nucleon resonances and LT is insensitive to the resonance, it is expected that the pair of forward spin polarizabilities should provide benchmark tests of the current understanding of the chiral dynamics of QCD. The new results on LT show significant disagreement with chiral perturbation theory calculations, while the data for 0 at low Q2 are in good agreement with a next-to-leading-order relativistic baryon chiral perturbation theory calculation. The data show good agreement with the phenomenological MAID model.
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| 9. |
- Amarian, M, et al.
(författare)
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Q2 Evolution of the Neutron Spin Structure Moments using a He-3 Target
- 2004
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Ingår i: Physical Review Letters. - 1079-7114. ; 92
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Tidskriftsartikel (refereegranskat)abstract
- We have measured the spin structure functions g1 and g2 of 3He in a double-spin experiment by inclusively scattering polarized electrons at energies ranging from 0.862 to 5.058 GeV off a polarized 3He target at a 15.5° scattering angle. Excitation energies covered the resonance and the onset of the deep inelastic regions. We have determined for the first time the Q2 evolution of 1(Q2)=g1(x,Q2)dx, 2(Q2)=g2(x,Q2)dx, and d2(Q2)=x2[2g1(x,Q2)+3g2(x,Q2)]dx for the neutron in the range 0.1Q20.9 GeV2 with good precision. 1(Q2) displays a smooth variation from high to low Q2. The Burkhardt-Cottingham sum rule holds within uncertainties and d2 is nonzero over the measured range.
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| 10. |
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| 11. |
- Aniol, K. A., et al.
(författare)
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Measurement of the neutral weak form factors of the proton
- 1999
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Ingår i: Physical Review Letters. - 1079-7114. ; 82:6, s. 1096-1100
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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.
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| 12. |
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| 13. |
- Behmokhtar, F, et al.
(författare)
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Measurement of the He3(e,e'p)pn reaction at high missing energies and momenta
- 2005
-
Ingår i: Physical Review Letters. - 1079-7114. ; 94:8
-
Tidskriftsartikel (refereegranskat)abstract
- Results of the Jefferson Lab Hall A quasielastic 3He(e,ep)pn measurements are presented. These measurements were performed at fixed transferred momentum and energy, q=1502 MeV/c and =840 MeV, respectively, for missing momenta pm up to 1 GeV/c and missing energies in the continuum region, up to pion threshold; this kinematic coverage is much more extensive than that of any previous experiment. The cross section data are presented along with the effective momentum density distribution and compared to theoretical models.
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| 14. |
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| 15. |
- Briscoe, W. J., et al.
(författare)
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Nuclear physics program at MAX-lab
- 2009
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Ingår i: Chinese Physics C. - : IOP Publishing. - 0899-9996 .- 1674-1137. ; 33:12, s. 1159-1166
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Konferensbidrag (refereegranskat)abstract
- The upgrade of the MAX-lab Injector and the construction of MAX III, provided the opportunity for upgrading the tagged-photon facility and thus lead to the possibility of more extensive program in nuclear physics research This upgrade increased the injected electron energy to all eventual maximum of 250 MeV and allows for the extraction of electrons from the MAX I ring operated in the stretcher mode The first stretched bean was delivered in September 2005. The tagged-photon facility was commissioned in parallel with the commissioning of new experimental equipment. The PAC approved experimental program is current in progress, including measurement of pion photoproduction below the Delta(1232) The efforts at the tagged photon-facility are pursed within all international collaboration with around fifty members
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| 16. |
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| 17. |
- Chirapatpimol, K, et al.
(författare)
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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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| 18. |
- Dijulio, Douglas D., et al.
(författare)
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Characterization of the radiation background at the Spallation Neutron Source
- 2016
-
Ingår i: VI European Conference On Neutron Scattering (ECNS2015). - : IOP Publishing. ; 746:1
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Konferensbidrag (refereegranskat)abstract
- We present a survey of the radiation background at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory, TN, USA during routine daily operation. A broad range of detectors was used to characterize primarily the neutron and photon fields throughout the facility. These include a WENDI-2 extended range dosimeter, a thermoscientific NRD, an Arktis He-4 detector, and a standard Nal photon detector. The information gathered from the detectors was used to map out the neutron dose rates throughout the facility and also the neutron dose rate and flux profiles of several different beamlines. The survey provides detailed information useful for developing future shielding concepts at spallation neutron sources, such as the European Spallation Source (ESS), currently under construction in Lund, Sweden.
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| 19. |
- Dutta, D, et al.
(författare)
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Nuclear transparency with the gamma n ->pi(-)p process in He-4
- 2003
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 68:2: 021001
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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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| 20. |
- Feldman, G., et al.
(författare)
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Compton scattering from deuterium and the polarizabilities of the neutron
- 2008
-
Ingår i: Few-Body Systems. - : Springer Science and Business Media LLC. - 0177-7963 .- 1432-5411. ; 44:1-4, s. 325-328
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Konferensbidrag (refereegranskat)abstract
- A new program of Compton scattering on deuterium is under way at the tagged-photon facility at MAX-Lab in Lund, Sweden. We will measure differential cross sections between 60A degrees and 150A degrees over the photon energy range 60-115 MeV in 5 MeV steps, with the ultimate goal of obtaining new precision information on the electric and magnetic polarizabilities of the neutron.
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| 21. |
- Fissum, Kevin
(författare)
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Dynamics of the quasielastic O-16(e,ep) reaction at Q2 = 0.8 (GeV/c)2
- 2004
-
Ingår i: Physical Review C: covering nuclear physics. ; 70:3
-
Tidskriftsartikel (refereegranskat)abstract
- The physics program in Hall A at Jefferson Lab commenced in the summer of 1997 with a detailed investigation of the 16O(e,ep) reaction in quasielastic, constant (q,) kinematics at Q20.8 (GeV/c)2, q1 GeV/c, and 445 MeV. Use of a self-calibrating, self-normalizing, thin-film waterfall target enabled a systematically rigorous measurement. Five-fold differential cross-section data for the removal of protons from the 1p-shell have been obtained for 0
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| 22. |
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| 23. |
- Fissum, Kevin, et al.
(författare)
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High-resolution measurement of the 12C(γ,p)11B reaction to excited states for Eγ=50–70MeV
- 1998
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Ingår i: Physical Review C: covering nuclear physics. - 2469-9985. ; 58:4, s. 2167-2173
-
Tidskriftsartikel (refereegranskat)abstract
- Relative population of states in 11B following the 12C(γ,p) reaction has been measured with high resolution using the deexcitation γ-ray technique. The states near 7 MeV in 11B are clearly resolved and the measured population clarifies earlier conflicting data. Comparison of the results with new calculations indicates the importance of both one-nucleon and multinucleon processes.
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| 24. |
- Fissum, Kevin
(författare)
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Proton elastic form factor ratios to Q^2 = 1.5 GeV^2 by polarization transfer
- 2005
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Ingår i: Physical Review C: covering nuclear physics. - 2469-9985. ; 71, s. 069902-069902
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Tidskriftsartikel (refereegranskat)abstract
- This paper was published online on 20 May 2005 without several of the authors’ corrections incorporated. Equation (13) has been replaced. The captions of Figs. 16–18 have also been replaced. Typographical errors on pages 4, 6, 14, 15, 18, 19, 22, and 24 have all been corrected. The paper has been corrected as of 8 June 2005. The text is correct in the printed version of the journal.
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| 25. |
- Fissum, Kevin
(författare)
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Q^2 Dependence of Quadrupole Strength in the \gamma*p -> Delta^+(1232) -> p\pi^0 transition
- 2002
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Ingår i: Physical Review Letters. - 1079-7114. ; 88, s. 122001-122001
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Tidskriftsartikel (refereegranskat)abstract
- Models of baryon structure predict a small quadrupole deformation of the nucleon due to residual tensor forces between quarks or distortions from the pion cloud. Sensitivity to quark versus pion degrees of freedom occurs through the Q2 dependence of the magnetic (M1+), electric (E1+), and scalar (S1+) multipoles in the γ∗p→Δ+→pπ0 transition. We report new experimental values for the ratios E1+/M1+ and S1+/M1+ over the range Q2=0.4–1.8GeV2, extracted from precision p(e,e′p)π0 data using a truncated multipole expansion. Results are best described by recent unitary models in which the pion cloud plays a dominant role.
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| 26. |
- Fissum, Kevin
(författare)
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Recent Results and Future Plans at MAX-lab
- 2007
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Ingår i: Chiral Dynamics 2006. - : WORLD SCIENTIFIC. ; , s. 378-379
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Konferensbidrag (refereegranskat)abstract
- Recent results obtained for the 4He(γ,n) reaction prior to the facility upgrade are presented. Future plans for measuring Compton scattering from the deuteron at the upgraded facility are discussed.
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| 27. |
- Fissum, Kevin, et al.
(författare)
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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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| 28. |
- Ganenko, V., et al.
(författare)
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Linearly polarized photon beam at MAX-lab
- 2014
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 763, s. 137-149
-
Tidskriftsartikel (refereegranskat)abstract
- A linearly polarized photon beam has been produced at MAX-lab using the coherent bremsstrahlung of electrons with an energy of 192.6 MeV in a 0.1 mm thick diamond crystal. The intensity and shape of the coherent maxima and their dependence on the crystal orientation are similar to the features observed at higher electron energies (similar to 1 GeV) and are well described by coherent bremsstrahlung theory. The linear polarization of the uncollimated beam at the coherent peak energy approximate to 50-60 MeV is about 20% and can be increased to 40-45% if collimation of half the characteristic angle is used At present the degree of polarization is high enough to allow the study of polarization observables in photo-nuclear reactions at MAX-lab in the energy range from Giant Dipole Resonance up to approximate to 80 MeV. (C) 2014 Elsevier B.V. All rights reserved.
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| 29. |
- Ganenko, V., et al.
(författare)
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Production of linearly polarized photon beam at MAX-lab
- 2009
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Ingår i: Voprosy Atomnoj Nauki i Techniki. - 1562-6016. ; :3, s. 95-102
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Tidskriftsartikel (refereegranskat)abstract
- Spectra of coherent bremsstrahlung from the diamond crystal in the laboratory MAX-lab on the accelerator MAX-I are measured at the energy of the electronic beam 144 MeV. First in the laboratory MAX-lab a source of the polarized photon radiation was created. Photon spectra were compared with theoretical calculations, that allow to estimate a magnitude of photon polarization, which is sufficient, for performing the nuclear experiments in the intermediate energy range.
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| 30. |
- Gao, Jinlong, et al.
(författare)
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Dynamical Relativistic Effects in Quasielastic 1p-Shell Proton Knockout from 16O
- 2000
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Ingår i: Physical Review Letters. - 1079-7114. ; 84:15, s. 3265-3269
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Tidskriftsartikel (refereegranskat)abstract
- We have measured the cross section for quasielastic 1p-shell proton knockout in the 16O(e,e′p) reaction at ω=0.439GeV and Q2=0.8(GeV/c)2 for missing momentum Pmiss≤355MeV/c. We have extracted the response functions RL+TT, RT, RLT, and the left-right asymmetry, ALT, for the 1p1/2 and the 1p3/2 states. The data are well described by relativistic distorted wave impulse approximation calculations. At large Pmiss, the structure observed in ALT indicates the existence of dynamical relativistic effects.
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| 31. |
- Gayou, O, et al.
(författare)
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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.
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| 32. |
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| 33. |
- Gayou, O., et al.
(författare)
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Measurements of the elastic electromagnetic form factor ratio μpGEp/GMp via polarization transfer
- 2001
-
Ingår i: Physical Review C: covering nuclear physics. - 2469-9985. ; 64:3
-
Tidskriftsartikel (refereegranskat)abstract
- We present measurements of the ratio of the proton elastic electromagnetic form factors, μpGEp/GMp. The Jefferson Lab Hall A Focal Plane Polarimeter was used to determine the longitudinal and transverse components of the recoil proton polarization in ep elastic scattering; the ratio of these polarization components is proportional to the ratio of the two form factors. These data reproduce the observation of Jones et al. [Phys. Rev. Lett. 84, 1398 (2000)], that the form factor ratio decreases significantly from unity above Q2=1GeV2.
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| 34. |
- Golubev, Pavel, et al.
(författare)
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Pion Emission in H-2,C-12,Al-27(gamma,pi+) Reactions at Threshold
- 2008
-
Ingår i: Nuclear Physics, Section A. - : Elsevier BV. - 0375-9474 .- 1873-1554. ; 806:1-4, s. 216-229
-
Tidskriftsartikel (refereegranskat)abstract
- The very first data from MAX-lab in Lund, Sweden on pion photoproduction at threshold energies are presented. The decrease of the total π+ yield in γ+12C, 27Al reactions below 200 MeV as well as the dσ/dΩ cross-section data essentially follow the predictions of an intranuclear-cascade model with an attractive potential for the pion–nucleus interaction. However, View the MathML source, cross-section data at 176 MeV show deviations which call for refinements of the model and possibly also for the inclusion of coherent pion-production mechanisms.
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| 35. |
- Jebali, R., et al.
(författare)
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A first comparison of the responses of a He-4-based fast-neutron detector and a NE-213 liquid-scintillator reference detector
- 2015
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576 .- 0167-5087. ; 794, s. 102-108
-
Tidskriftsartikel (refereegranskat)abstract
- A first comparison has been made between the pulse-shape discrimination characteristics of a novel He-4-based pressurized scintillation detector and a NE-213 liquicl-scintillator reference detector using an Am/Be mixed-field neutron and gamma-ray source and a high-resolution scintillation-pulse digitizer. In particular, the capabilities of the two fast neutron detectors to discriminate between neutrons and gamma-rays were investigated. The NE-213 liquicl-scintillator reference cell produced a wide range of scintillation-light yields in response to he gamma-ray field of the source. In stark contrast, clue to the size and pressure of the He-4 gas volume, the He-4-based detector registered a maximum scintillation-light yield of 750 keV(ee) to the same gamma-ray field. Pulse-shape discrimination for particles with scintillation-light yields of more than 750 keV(ee) was excellent in the case of the He-4-based detector. Above 750 keV(ee) its signal was unambiguously neutron, enabling particle identification based entirely upon the amount of scintillation light produced. (C) 2015 The Authors. Published by Elsevier B.V.
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| 36. |
- Jones, M. K., et al.
(författare)
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GEp/GMp Ratio by Polarization Transfer in \vec{e}p→e\vec{p}
- 2000
-
Ingår i: Physical Review Letters. - 1079-7114. ; 84:7, s. 1398-1402
-
Tidskriftsartikel (refereegranskat)abstract
- The ratio of the proton's elastic electromagnetic form factors, GEp/GMp, was obtained by measuring Pt and Pℓ, the transverse and the longitudinal recoil proton polarization, respectively. For elastic →ep→e→p, GEp/GMp is proportional to Pt/Pℓ. Simultaneous measurement of Pt and Pℓ in a polarimeter provides good control of the systematic uncertainty. The results for the ratio GEp/GMp show a systematic decrease as Q2 increases from 0.5 to 3.5GeV2, indicating for the first time a definite difference in the spatial distribution of charge and magnetization currents in the proton.
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| 37. |
- Karlsson, Martin, et al.
(författare)
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Measurement of the differential cross section for the two-body photodisintegration of He-3 at theta(LAB)=90 degrees using tagged photons in the energy range 14-31 MeV
- 2009
-
Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 80:4
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Tidskriftsartikel (refereegranskat)abstract
- The two-body photodisintegration of He-3 has been investigated using tagged photons with energies from 14-31 MeV at MAX-lab in Lund, Sweden. The two-body breakup channel was unambiguously identified by the (nonsimultaneous) detection of both protons and deuterons. This approach was made feasible by the overdetermined kinematic situation afforded by the tagged-photon technique. Proton-and deuteron-energy spectra were measured using four silicon surface-barrier detector telescopes located at a laboratory angle of 90 degrees with respect to the incident photon-beam direction. Average statistical and systematic uncertainties of 5.7% and 6.6% in the differential cross section were obtained for 11 photon-energy bins with an average width of 1.2 MeV. The results are compared to previous experimental data measured at comparable photon energies as well as to the results of two recent Faddeev calculations which employ realistic potential models and take into account three-nucleon forces and final-state interactions. Both the accuracy and precision of the present data are improved over those obtained in the previous measurements. The data are in good agreement with most of the previous results, and favor the inclusion of three-nucleon forces in the calculations.
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| 38. |
- Kelly, J J, et al.
(författare)
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Recoil Polarization for Delta Excitation in Pion Electroproduction
- 2005
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Ingår i: Physical Review Letters. - 1079-7114. ; 95
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Tidskriftsartikel (refereegranskat)abstract
- We measured angular distributions of recoil-polarization response functions for neutral pion electroproduction for W=1.23 GeV at Q2=1.0 (GeV/c)2, obtaining 14 separated response functions plus 2 Rosenbluth combinations; of these, 12 have been observed for the first time. Dynamical models do not describe quantities governed by imaginary parts of interference products well, indicating the need for adjusting magnitudes and phases for nonresonant amplitudes. We performed a nearly model-independent multipole analysis and obtained values for Re (S1+/M1+)=-(6.84±0.15)% and Re (E1+/M1+)=-(2.91±0.19)% that are distinctly different from those from the traditional Legendre analysis based upon M1+ dominance and 1 truncation.
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| 39. |
- Kelly, J. J., et al.
(författare)
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Recoil polarization measurements for neutral pion electroproduction at Q(2)=1(GeV/c)(2) near the Delta resonance
- 2007
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 75:2
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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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| 40. |
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| 41. |
- Laveissière, G, et al.
(författare)
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Measurement of the Generalized Polarizabilities of the Proton in Virtual Compton Scattering at Q2 = 0.92 and 1.76 GeV2
- 2004
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Ingår i: Physical Review Letters. - 1079-7114. ; 93
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Tidskriftsartikel (refereegranskat)abstract
- We report a virtual Compton scattering study of the proton at low c.m. energies. We have determined the structure functions PLL–PTT/and PLT, and the electric and magnetic generalized polarizabilities (GPs) E(Q2) and M(Q2) at momentum transfer Q2=0.92 and 1.76 GeV2. The electric GP shows a strong falloff with Q2, and its global behavior does not follow a simple dipole form. The magnetic GP shows a rise and then a falloff; this can be interpreted as the dominance of a long-distance diamagnetic pion cloud at low Q2, compensated at higher Q2 by a paramagnetic contribution from N intermediate states.
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| 42. |
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| 43. |
- López Herraiz, Joaquín, et al.
(författare)
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(e,e'p) reaction at true quasielastic kinematics in 16O, 12C, and 208Pb at JLab
- 2009
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Ingår i: La Rabida 2009, International Scientific Meeting on Nuclear Physics: Basic Concepts in Nuclear Physics : Theory Experiements and Applications - Theory Experiements and Applications. - : AIP. ; , s. 225-226
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Konferensbidrag (refereegranskat)abstract
- The reactions 16O(e,e'p) 15N, 208Pb(e,e'p) 207Tl and 12C(e,e'p) 11B were measured in experiments E00-102 and E06-007 performed at JLab (VA, USA) at true quasielastic kinematics (xB = 1) with constant energy (ω) and momentum (q) transferred over a wide pmiss range. These experiments address several open issues in nuclear structure such as the role of relativity and of long-range correlations in the description of nuclei as well as a possible dependence of the spectroscopic factors on Q2. Preliminary experimental results and theoretical predictions from a fully relativistic DWIA model carefully averaged over the experimental acceptances are shown.
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| 44. |
- Lundin, Magnus, et al.
(författare)
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Compton scattering from the deuteron and extracted neutron polarizabilities
- 2003
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Ingår i: Physical Review Letters. - 1079-7114. ; 90:19
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Tidskriftsartikel (refereegranskat)abstract
- Differential cross sections for Compton scattering from the deuteron were measured at MAX-Lab for incident photon energies of 55 and 66 MeV at nominal laboratory angles of 45degrees, 125degrees, and 135degrees. Tagged photons were scattered from liquid deuterium and detected in three NaI spectrometers. By comparing the data with theoretical calculations in the framework of a one-boson-exchange potential model, the sum and the difference of the isospin-averaged nucleon polarizabilities, alpha(N) + beta(N) = 17.4 +/- 3.7 and alpha(N) - beta(N) = 6.4 +/- 2.4 (in units of 10(-4) fm(3)), have been determined. By combining the latter with the global-averaged value for alpha(p) - beta(p) and using the predictions of the Baldin sum rule for the sum of the nucleon polarizabilities, we have obtained values for the neutron electric and magnetic polarizabilities of alpha(n) = 8.8 +/- 2.4(total) +/- 3.0(model) and beta(n) = 6.5 -/+ 2.4(total) -/+ 3.0(model), respectively.
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| 45. |
- Marcks von Wurtemberg, Klas, et al.
(författare)
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The response of lead-tungstate scintillators (PWO) to photons with energies in the range 13 MeV-64 MeV
- 2012
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576 .- 0167-5087. ; 679, s. 36-43
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Tidskriftsartikel (refereegranskat)abstract
- The response of a matrix of 25 lead tungstate (PWO) scintillator detectors, operated at -25 degrees C, to photons in the range 13 MeV-64 MeV has been measured at the tagged-photon facility at MAX-lab, Lund. The tapered PWO crystals, each with a length of 200 mm and a cross-section of 24.4 x 24.4 mm(2) in the front end, read out by 19 mm photomultiplier tubes, were arranged in a 5 x 5 matrix. The response was measured for photons directed towards the centre of the central crystal as well as for photons directed towards the corner of the central crystal, where four crystals meet. The obtained energy resolution surpasses what has been published so far and is close to the limit given by Poisson statistics and escaped energy. For photons directed towards the centre(corner) of the central crystal the relative energy resolution, defined as (FWHM/2.35)/E-gamma, decreases from 7.3%(11.0%) at E-gamma = 13 MeV to 3.3%(3.6%) at E-gamma = 64 MeV. The reconstructed point of impact of a photon in this energy range is determined with an uncertainty (one standard deviation) of 7.3 +/- 0.1 mm.
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| 46. |
- Margaryan, Ashot, et al.
(författare)
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Low-Pressure MWPC System for the detection of Alpha-Particles and Fission Fragments
- 2010
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Ingår i: Armenian Journal of Physics. - 1829-1171. ; 3:4, s. 282-291
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Tidskriftsartikel (refereegranskat)abstract
- A low-pressure, position-sensitive, multi-wire proportional chamber (LPMWPC) system with an active area 12×12 cm 2 for the detection of heavy nuclear fragments, has been developed for use in tagged photon beam experiments. The LPMWPC system can be operated in single as well as double step operational modes. In the case of double step operational mode with a high gas amplification factor, signals from α-particles reside well above the electronic noise. Typical energy loss spectra of alpha particles and fission fragments (FF) obtained from a 252 Cf source are shown and discussed. The pulse height distributions of α-particles have a Landau distribution shape, while the pulse height distribution of FFs differs from Gaussian shape. It has long tails at both low-and high-energy sides. The average pulse height ratio of alpha particles and FF's is close to the theoretical value and amounts to about 1/80.
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| 47. |
- Myers, L. S., et al.
(författare)
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Compton scattering from C-12 using tagged photons in the energy range 65-115 MeV
- 2014
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 89:3
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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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| 48. |
- Myers, L. S., et al.
(författare)
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Compton scattering from the deuteron below pion-production threshold
- 2015
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 92:2
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Tidskriftsartikel (refereegranskat)abstract
- Differential cross sections for elastic scattering of photons from the deuteron have recently been measured at the Tagged-Photon Facility at the MAX IV Laboratory in Lund, Sweden. These first new measurements in more than a decade further constrain the isoscalar electromagnetic polarizabilities of the nucleon and provide the first-ever results above 100 MeV, where the sensitivity to the polarizabilities is increased. We add 23 points between 70 and 112 MeV, at angles 60 degrees, 120 degrees, and 150 degrees. Analysis of these data using a chiral effective field theory indicates that the cross sections are both self-consistent and consistent with previous measurements. Extracted values of alpha(s) = [12.1 +/- 0.8(stat) +/- 0.2(BSR) +/- 0.8(th)] x 10(-4) fm(3) and beta(s) = [2.4 +/- 0.8(stat) +/- 0.2(BSR) +/- 0.8(th)] x 10(-4) fm(3) are obtained from a fit to these 23 new data points. This paper presents in detail the experimental conditions and the data analysis used to extract the cross sections.
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| 49. |
- Myers, L S, et al.
(författare)
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Measurement of compton scattering from the deuteron and an improved extraction of the neutron electromagnetic polarizabilities.
- 2014
-
Ingår i: Physical Review Letters. - 1079-7114. ; 113:26
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Tidskriftsartikel (refereegranskat)abstract
- The electromagnetic polarizabilities of the nucleon are fundamental properties that describe its response to external electric and magnetic fields. They can be extracted from Compton-scattering data-and have been, with good accuracy, in the case of the proton. In contradistinction, information for the neutron requires the use of Compton scattering from nuclear targets. Here, we report a new measurement of elastic photon scattering from deuterium using quasimonoenergetic tagged photons at the MAX IV Laboratory in Lund, Sweden. These first new data in more than a decade effectively double the world data set. Their energy range overlaps with previous experiments and extends it by 20 MeV to higher energies. An analysis using chiral effective field theory with dynamical Δ(1232) degrees of freedom shows the data are consistent with and within the world data set. After demonstrating that the fit is consistent with the Baldin sum rule, extracting values for the isoscalar nucleon polarizabilities, and combining them with a recent result for the proton, we obtain the neutron polarizabilities as α_{n}=[11.55±1.25(stat)±0.2(BSR)±0.8(th)]×10^{-4} fm^{3} and β_{n}=[3.65∓1.25(stat)±0.2(BSR)∓0.8(th)]×10^{-4} fm^{3}, with χ^{2}=45.2 for 44 degrees of freedom.
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| 50. |
- Myers, L. S., et al.
(författare)
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Monte Carlo simulation of the photon-tagger focal-plane electronics at the MAX IV laboratory
- 2013
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 729, s. 707-717
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Tidskriftsartikel (refereegranskat)abstract
- Rate-dependent effects in the electronics used to instrument the tagger focal plane at the MAX IV Laboratory have been investigated using the novel approach of Monte Carlo simulation. Results are compared to analytical calculations as well as experimental data for both specialized testing and production running to demonstrate a thorough understanding of the behavior of the detector system.(C) 2013 Elsevier By. All rights reserved.
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