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I. Ionita - One of the best experts on this subject based on the ideXlab platform.

  • The Resolution Function for a pulsed-source TOF neutron spectrometer with crystal monochromator
    Physica B-condensed Matter, 2004
    Co-Authors: I. Ionita
    Abstract:

    Abstract The matrix procedure to compute the Resolution Function for a given experimental configuration is briefly given followed by its application to a particular one, a pulsed source TOF neutron spectrometer with crystal monochromator. Both the direct and the inverse geometry are considered. As for the matrix procedure a normal 486 PC is quite suited with computing times of 1–2 s in comparison with the Monte Carlo computing technique for which special computer configurations are needed, the matrix procedure should be preferred when the normal approximation is still valid and if a precise description of the line profile is not required.

  • The Resolution Function for a pulsed-source TOF neutron spectrometer
    Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2003
    Co-Authors: I. Ionita
    Abstract:

    Abstract The matrix procedure to compute the Resolution Function for a given experimental configuration is briefly given followed by its application to a particular one, a pulsed source TOF neutron spectrometer. All the corresponding relevant configurations are considered. For crystal and polycrystalline filter as monochromator both the direct and the inverse geometry are considered. As for the matrix procedure a normal 486 PC is quite suited with computing times of 1– 2 s in comparison with the Monte Carlo computing technique for which special computer configurations are needed; the matrix procedure should be preferred when the normal approximation is still valid and if a precise description of the line profile is not required.

  • The Resolution Function for a time-of-flight hybrid neutron spectrometer with crystal monochromator and chopper
    Journal of Applied Crystallography, 2002
    Co-Authors: I. Ionita
    Abstract:

    A procedure for computing the Resolution Function for a time-of-flight hybrid neutron spectrometer with crystal monochromator and chopper using the matrix computation technique is presented. A brief general description of the matrix computation technique and the computer program HYBR, implementing the matrix procedure, are also presented. Some ideal focusing conditions deduced by compensating the major contributions to the variances of the scan variable are given; these ideal conditions can be used as a zeroth-order approximation in a numerical optimization procedure.

  • The Resolution Function for a time-of-flight diffractometer with curved slits chopper
    Journal of Applied Crystallography, 2001
    Co-Authors: I. Ionita
    Abstract:

    A procedure is presented for computing the Resolution Function for a time-of-flight diffractometer with curved slits chopper using the matrix computation technique. Some focusing conditions are deduced by compensating the major contributions to the variance of the scan variables; these conditions refer to the optimum sample and detector inclination angle and to the optimum chopper angular speed.

Jan Skov Pedersen - One of the best experts on this subject based on the ideXlab platform.

  • Resolution Function for Two-Axis Specular Neutron Reflectivity
    Journal of Applied Crystallography, 1996
    Co-Authors: Wim G. Bouwman, Jan Skov Pedersen
    Abstract:

    The Resolution Function for specular neutron reflectivity measurements of flat samples is calculated. The results are also applicable to some X-ray reflectivity set-ups. In a basic approach, the contributions of the wavelength spread and the angular divergence are calculated. The method of combining these contributions is discussed. These calculations are compared with some measured reflectivity curves. The calculations are checked with an analytical beam analysis method that takes directly into account the coupling between the angle, position and wavelength of the neutrons.

  • The three-dimensional Resolution Function for small-angle scattering and Laue geometries
    Journal of Applied Crystallography, 1995
    Co-Authors: Pernille Harris, B. Lebech, Jan Skov Pedersen
    Abstract:

    An analytical calculation of the three-dimensional Resolution Function for a small-angle neutron scattering set-up has been performed by application of a combination of phase-space analysis and Gaussian approximations for the neutron distribution as well as for the transmission Functions of the different apertures. Small-angle approximations for the scattering angles have not been used and the results can be applied to other scattering geometries of the same type. The results are compared with Monte Carlo simulations and good agreement is found. To apply the method for analysing single-crystal diffraction data, a finite mosaic spread of the crystal and finite correlation widths of the Bragg reflections have been introduced in the cross section. The measured intensity (scattering Function) is the cross section convoluted with the Resolution Function. The mosaicity and the finite correlation widths were described by Gaussian distribution Functions and the convolutions were done analytically. The model cross section smeared by the Resolution Function has been applied to the analysis of single-crystal data of the long-range magnetic order in MnSi.

  • Resolution Function and Flux at the Sample for Small-Angle X-ray Scattering Calculated in Position-Angle-Wavelength Space
    Journal of Applied Crystallography, 1991
    Co-Authors: Jan Skov Pedersen, Christian Riekel
    Abstract:

    A method for calculating the flux at the sample position and the Resolution Function based on the general description of synchrotron X-ray beamlines in position–angle–wavelength space has been developed. A mathematical formulation is presented, in which source, transmission Function for the slits and acceptance windows of the monochromator crystals are approximated by Gaussian Functions. These approximations allow all of the algebra in connection with combining the different contributions to be done analytically. When the beam passes the various components of the beamline, such as flight paths, monochromators and mirrors, it results in coordinate transformations in parameter space. By inserting the transformations in the intensity distribution of the source, transmission Functions of the slits and acceptance windows of the monochromators, these are transformed to the position of the sample. Their product gives the intensity distribution at this position and from this the Resolution Function in reciprocal space is calculated. The Resolution of the detector is easily included by a convolution. The transmissions of the slits and the acceptance windows of the monochromator crystals have been normalized to give the same integrated transmission and reflectivities as the Functions they approximate. Therefore the flux at the sample position can be calculated by multiplication of the brilliance of the source and the result obtained from an integration of the distribution over the two position parameters, the two angle parameters and the wavelength. The theory has been applied to an example and gives reasonable results for sample intensity and Resolution Function.

H. Nagasawa - One of the best experts on this subject based on the ideXlab platform.

  • The Resolution Function of a Triple-Crystal Diffractometer for High-Energy Synchrotron Radiation in Nondispersive Laue Geometry
    Journal of Applied Crystallography, 1994
    Co-Authors: H. B. Neumann, U. Rütt, R. Bouchard, J.r. Schneider, H. Nagasawa
    Abstract:

    The k-space Resolution Function of a triple-crystal diffractometer is calculated for an arrangement of three perfect silicon single crystals Bragg diffracting in nondispersive Laue geometry. A comparison is made with the results of measurements using synchrotron radiation in the energy range from 80 to 150 keV. In this case, absorption is very weak and according to dynamical theory the width of the diffraction pattern of thick perfect single crystals is proportional to the wavelength λ, whereas its Lorentzian tails are proportional to λ2. Together with the fact that the Bragg angles are only of the order of 2°, this leads to a concentration of the starlike k-space Resolution Function into a narrow band parallel to the reciprocal-lattice vector G. For diffraction of 80 keV synchrotron radiation at the silicon 111 reflection, the full width at half-maximum (FWHM) of the intensity distribution in the scattering plane is 1.1 × 10−5 A−1 perpendicular to G and 2.2 × 10−4 A−1 parallel to G. The observed differences in the contributions from monochromator and analyzer crystal to the Resolution Function are explained by the finite width of the electronic window of the detector counting chain and the non-Bragg scattering contribution from the crystals. If annealed Czochralski-grown silicon single crystals with a mosaicity of ~3′′ are used as monochromator and analyzer, the Resolution is reduced by one order of magnitude, but for studies of imperfect samples or of diffuse scattering large gains in intensity can be accomplished this way.

H. B. Neumann - One of the best experts on this subject based on the ideXlab platform.

  • The Resolution Function of a Triple-Crystal Diffractometer for High-Energy Synchrotron Radiation in Nondispersive Laue Geometry
    Journal of Applied Crystallography, 1994
    Co-Authors: H. B. Neumann, U. Rütt, R. Bouchard, J.r. Schneider, H. Nagasawa
    Abstract:

    The k-space Resolution Function of a triple-crystal diffractometer is calculated for an arrangement of three perfect silicon single crystals Bragg diffracting in nondispersive Laue geometry. A comparison is made with the results of measurements using synchrotron radiation in the energy range from 80 to 150 keV. In this case, absorption is very weak and according to dynamical theory the width of the diffraction pattern of thick perfect single crystals is proportional to the wavelength λ, whereas its Lorentzian tails are proportional to λ2. Together with the fact that the Bragg angles are only of the order of 2°, this leads to a concentration of the starlike k-space Resolution Function into a narrow band parallel to the reciprocal-lattice vector G. For diffraction of 80 keV synchrotron radiation at the silicon 111 reflection, the full width at half-maximum (FWHM) of the intensity distribution in the scattering plane is 1.1 × 10−5 A−1 perpendicular to G and 2.2 × 10−4 A−1 parallel to G. The observed differences in the contributions from monochromator and analyzer crystal to the Resolution Function are explained by the finite width of the electronic window of the detector counting chain and the non-Bragg scattering contribution from the crystals. If annealed Czochralski-grown silicon single crystals with a mosaicity of ~3′′ are used as monochromator and analyzer, the Resolution is reduced by one order of magnitude, but for studies of imperfect samples or of diffuse scattering large gains in intensity can be accomplished this way.

R Golub - One of the best experts on this subject based on the ideXlab platform.

  • the Resolution Function in neutron spin echo spectroscopy with three axis spectrometers
    Journal of Applied Crystallography, 2003
    Co-Authors: K Habicht, T Keller, R Golub
    Abstract:

    A Resolution Function for inelastic neutron spin-echo spectroscopy on a three-axis spectrometer is derived. Inelastic dispersive excitations where the tilted field technique applies are being considered. Using a Gaussian approximation of the transmission Function of the three-axis spectrometer and a second-order expansion of the total Larmor phase, the instrumental Resolution Function of an idealized spin-echo instrument is obtained. Furthermore, the Resolution Function is extended to include the effects of sample properties, such as mosaicity, spread in lattice spacings and the curvature of the four-dimensional dispersion surface in a line-width measurement.