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  • 1.
    Hartmann, Ola
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Fysik III.
    Karlsson, Erik
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Fysik III.
    Wäppling, Roger
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Fysik III.
    Seidel, Agneta
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Fysik III.
    Richter, Dieter
    Hempelmann, R
    Kossler, W. J.
    Hitti, B
    Kempton, J
    Lankford, W. F.
    Stronach, C. F.
    Muon Diffusion in Nb-H Systems1986In: Hyperfine Interactions, Vol. 31, p. 241-245Article in journal (Refereed)
  • 2.
    Hjorvarsson, B
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Andersson, G
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Karlsson, E
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Metallic superlattices: Quasi two-dimensional playground for hydrogen1997In: JOURNAL OF ALLOYS AND COMPOUNDS, ISSN 0925-8388, Vol. 253, p. 51-57Article in journal (Other scientific)
    Abstract [en]

    Hydrogen in superlattices, whose constituents have different hydrogen affinities, comprises a new class of hydrogen absorbing materials. The period of the absorption potential can be made as small as two monolayers, which implies highly anisotropic host m

  • 3.
    Karlsson, Erik B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Entanglement creation in Compton scattering of neutrons on protons and its possible energetic consequences2015In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 115, no 19, p. 1412-1416Article in journal (Refereed)
    Abstract [en]

    It has been predicted that entanglement creation should be associated with a lowering of energy (as well as the well-known decrease of entropy) for certain types of interaction potentials. This is a principally important question and it is shown here that np-scattering has specific features that would make it suitable for experimental tests of this prediction using neutron scattering on hydrogen at high angles. For this purpose, the evolution of n-p entanglement in Compton scattering on protons at epithermal energies (20-200 eV) is calculated over the separation distance 0-1 angstrom, corresponding to times up to 10(-15) s after the collision. If an energy transfer is associated with the entanglement, it ought to be observable under these measurement conditions.

  • 4.
    Karlsson, Erik B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Final state effects in the neutron Compton scattering on hydrogen molecules-a new approach2012In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 694, p. 286-296Article in journal (Refereed)
    Abstract [en]

    Compton scattering on hydrogen molecules (H-2, D-2) with neutrons in the 10-100 eV range has recently been discussed in connection with observations of certain unexplained shifts of the Compton peaks at higher scattering angles (possibly indicating a quantum entanglement effect on the sub-Is-time scale). It is therefore worthwhile to look somewhat deeper into the details of the scattering process for these particular systems. One main aspect is the specific situation valid for two-atomic molecules where the vibrational momenta lie only along the molecular axes, another concerns the validity of the impulse approximation and a third main aspect is related to the anomalous cross-sections in the H/D intensity ratios observed for mixed H-2/D-2 samples. In an alternative treatment of the so-called final state (FSE) effects the concept of scattering time is analyzed and the elastic slowing-down of the recoiling protons during this time is explicitly calculated and compared, first with those expected from standard FSE calculations and then with experimental data for one specifically chosen, well-studied system, the D-2 molecule. The results of the present FSE calculations differ from the standard ones in the high energy tail of the Compton peak, but agrees very well with experiment. Taking into account the line shape differences discussed here should also be of importance for the closer analysis of proton momentum distributions as well as for the interpretation of the H- and D- intensity anomalies.

  • 5.
    Karlsson, Erik B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Interpretation of the hydrogen anomaly in neutron and electron compton scattering2012In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 112, no 2, p. 587-602Article in journal (Refereed)
    Abstract [en]

    In Compton scattering with neutrons in the energy range 20-120 eV, it has been observed that the relative H/M cross sections in a variety of H-containing materials are 20-40% lower than expected from the composition ratio H/M (M being a heavier element in the same compound). The same phenomenon has also been observed in Compton scattering with electrons of 2 and 20 keV energy. There is, at present, no consensus about the reason for these anomalies. In this theory, they are explained as a result of interference when the scattering particle interacts with more than one hydrogen nucleus. The coherence volume of the actual setup, which limits the number of interfering particles, is therefore an important parameter. It is shown here that the large zero-point motion of the hydrogen nuclei leads to reductions in the scattering intensity from interfering pairs. Coherence is preserved over the sub-fs scattering times relevant for this process, even in the condensed systems studied. It is gradually lost when the scattering time is increased, which happens when the neutron energy is reduced (as reflected in lower anomalies for smaller scattering angles). Explicit expressions for the decoherence effect are presented and compared with experimental observation for a selection of observed H- and D-containing systems.

  • 6.
    Karlsson, Erik B.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics III.
    Proton-proton correlations in condensed matter2005In: Decoherence, Entanglement and Information Protection in Complex Quantum, Springer , 2005, p. 535-548Chapter in book (Refereed)
  • 7.
    Karlsson, ERik B.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics III.
    Quantum coherence in neutron scattering on protons2004In: Modern Physics Letters, Vol. B 18, no 247Article in journal (Other (popular scientific, debate etc.))
  • 8.
    Karlsson, Erik B.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics III.
    Quantum coherence of protons in metal hydrides2005In: J. Alloys and Compounds, Vol. 779, p. 404-406Article in journal (Refereed)
  • 9.
    Karlsson, Erik B
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    The hydrogen anomaly problem in neutron Compton scattering2018In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 93, no 3, article id 035801Article in journal (Refereed)
    Abstract [en]

    Neutron Compton scattering (also called 'deep inelastic scattering of neutrons', DINS) is a method used to study momentum distributions of light atoms in solids and liquids. It has been employed extensively since the start-up of intense pulsed neutron sources about 25 years ago. The information lies primarily in the width and shape of the Compton profile and not in the absolute intensity of the Compton peaks. It was therefore not immediately recognized that the relative intensities of Compton peaks arising from scattering on different isotopes did not always agree with values expected from standard neutron cross-section tables. The discrepancies were particularly large for scattering on protons, a phenomenon that became known as 'the hydrogen anomaly problem'. The present paper is a review of the discovery, experimental tests to prove or disprove the existence of the hydrogen anomaly and discussions concerning its origin. It covers a twenty-year-long history of experimentation, theoretical treatments and discussions. The problem is of fundamental interest, since it involves quantum phenomena on the subfemtosecond time scale, which are not visible in conventional thermal neutron scattering but are important in Compton scattering where neutrons have two orders of magnitude times higher energy. Different H-containing systems show different cross-section deficiencies and when the scattering processes are followed on the femtosecond time scale the cross-section losses disappear on different characteristic time scales for each H-environment. The last section of this review reproduces results from published papers based on quantum interference in scattering on identical particles (proton or deuteron pairs or clusters), which have given a quantitative theoretical explanation both regarding the H-cross-section reduction and its time dependence. Some new explanations are added and the concluding chapter summarizes the conditions for observing the specific quantum phenomena observed in neutron Compton scattering on protons and deuterons in condensed systems.

  • 10.
    Karlsson, Erik B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    The positive muon implanted in metals - a story full of surprises2014In: The European Physical Journal H, ISSN 2102-6459, Vol. 39, no 3, p. 303-323Article in journal (Refereed)
    Abstract [en]

    During the period 1975-1990 there was an intense development, at some accelerator laboratories, of a new spectroscopy based on the interaction of an elementary particle, the positive muon, with local magnetic fields present in magnets and superconductors. It was called mu SR (or in some applications MuSR), which stands for Muon Spin Rotation or Muon Spin Relaxation. At the present time this spectroscopy has given access to detailed information (often unobtainable with other means), on a large number of magnetic, semiconducting and superconducting systems, but the present article deals with another aspect of mu SR, namely the information it could provide on how a light positive particle behaves when placed in a metallic environment. This behaviour has much in common with that of the technologically important "hydrogen in metal"-problem, but could now be studied in a very direct way since the positive muon is radioactive and sends out an easily detectable signal. This signal contains information on the particle's local environment, its motion from one lattice position to another, its trapping and release from other impurity atoms in the metal and also on the character of the motion itself, particularly at low temperatures where quantum effects dominate. It took nearly 15 years to fully interpret and understand these phenomena which is the topic of the present historic presentation.

  • 11.
    Karlsson, Erik B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Hartmann, Ola
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Chatzidimitriou-Dreismann, C. A.
    Tech Univ Berlin, Inst Chem, Sekr C2, D-10623 Berlin, Germany..
    Abdul-Redah, T.
    Tech Univ Berlin, Inst Chem, Sekr C2, D-10623 Berlin, Germany..
    The hydrogen anomaly in neutron Compton scattering: new experiments and a quantitative theoretical explanation2016In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 27, no 8, article id 085501Article in journal (Refereed)
    Abstract [en]

    No consensus has been reached so far about the hydrogen anomaly problem in Compton scattering of neutrons, although strongly reduced H cross-sections were first reported almost 20 years ago. Over the years, this phenomenon has been observed in many different hydrogen-containing materials. Here, we use yttrium hydrides as test objects, YH2, YH3, YD2 and YD3, Y(HxD1-x)(2) and Y(HxD1-x)(3), for which we observe H anomalies increasing with transferred momentum q. We also observe reduced deuteron cross-sections in YD2 and YD3 and have followed those up to scattering angles of 140 degrees corresponding to high momentum transfers. In addition to data taken using the standard Au-197 foils for neutron energy selection, the present work includes experiments with Rh-103 foils and comparisons were also made with data from different detector setups. The H and D anomalies are discussed in terms of the different models proposed for their interpretation. The 'electron loss model' (which assumes energy transfer to excited electrons) is contradicted by the present data, but it is shown here that exchange effects in scattering from two or more protons (or deuterons) in the presence of large zero-point vibrations, can explain quantitatively the reduction of the cross-sections as well as their q-dependence. Decoherence processes also play an essential role. In a scattering time representation, shake-up processes can be followed on the attosecond scale. The theory also shows that large anomalies can appear only when the neutron coherence lengths (determined by energy selection and detector geometry) are about the same size as the distance between the scatterers.

1 - 11 of 11
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