WK
W.H. Kraan
info
Please Note
<p>This page displays the records of the person named above and is not linked to a unique person identifier. This record may need to be merged to a profile.</p>
11 records found
1
Journal article
(2020)
-
W. H. Kraan, L. A. Akselrod, E. G. Yashina, A. A. Sumbatyan, S. V. Grigoriev
Abstract: We created software to simulate the Larmor precession in a setup for SESANS with adiabatic/radio frequency flippers in magnets designed to measure the time-of-flight on pulsed or stationary neutron sources. The values and spatial configurations of the magnetic fields of the existing prototype magnets we used as input data. For an empty setup, we calculate the polarization of a “divergent ribbon beam” 2 cm high, depending on the neutron wavelength λ. In the “scattering experiment”, we show how to convert λ to the “spin-echo length” δ. For λ = 10 Å, flippers at a distance of 140 cm and a radio frequency 1 MHz we find δ ≈ 10 μm. Extension to δ = 20 μm is realistic.
...
Abstract: We created software to simulate the Larmor precession in a setup for SESANS with adiabatic/radio frequency flippers in magnets designed to measure the time-of-flight on pulsed or stationary neutron sources. The values and spatial configurations of the magnetic fields of the existing prototype magnets we used as input data. For an empty setup, we calculate the polarization of a “divergent ribbon beam” 2 cm high, depending on the neutron wavelength λ. In the “scattering experiment”, we show how to convert λ to the “spin-echo length” δ. For λ = 10 Å, flippers at a distance of 140 cm and a radio frequency 1 MHz we find δ ≈ 10 μm. Extension to δ = 20 μm is realistic.
Journal article
(2017)
-
K. A. Pavlov, E. V. Velichko, V. N. Zabenkin, W. H. Kraan, C. P. Duif, W. G. Bouwman, Z. A. Mikhailovskaya, E. S. Buyanova, S. V. Grigoriev
The closed porous structure in ceramic materials is investigated by spin-echo small-angle neutron scattering. A series of ceramic samples of oxygen–ion conductors based on bismuth molybdate with the general formula Bi12.8X0.2Mo5O34 ± δ (X = Mg, Ba, Ca, Sr) is obtained by powder sintering for 6−45 h at a temperature close to the melting point. The samples are characterized by scanning electron microscopy and X-ray fluorescence analysis. It is found that they had a stoichiometric chemical composition, are singlephase, and contain clean pores between crystal grains. The pore size is determined by spin-echo small-angle neutron scattering and ranges from 2.2 to 3.5 μm. It is demonstrated that longer sintering times correspond to larger pores (the increase in their average diameter is as large as 30%). It is found that the studied materials lack a fractal pore structure.
...
The closed porous structure in ceramic materials is investigated by spin-echo small-angle neutron scattering. A series of ceramic samples of oxygen–ion conductors based on bismuth molybdate with the general formula Bi12.8X0.2Mo5O34 ± δ (X = Mg, Ba, Ca, Sr) is obtained by powder sintering for 6−45 h at a temperature close to the melting point. The samples are characterized by scanning electron microscopy and X-ray fluorescence analysis. It is found that they had a stoichiometric chemical composition, are singlephase, and contain clean pores between crystal grains. The pore size is determined by spin-echo small-angle neutron scattering and ranges from 2.2 to 3.5 μm. It is demonstrated that longer sintering times correspond to larger pores (the increase in their average diameter is as large as 30%). It is found that the studied materials lack a fractal pore structure.
Abstract
(2017)
-
Wicher Kraan, LA Akselrod, V. N. Zabenkin, Yu.O. Chetverikov, SV Grigoriev, A.A. Sumbatyan
Journal article
(2017)
-
Wicher Kraan, V.N. Zabenkin, LA Axelrod, Yu.O. Chetverikov, SV Grigoriev, E.G. Yashina, A.A. Sumbatyan
We made software to simulate Larmor precession in a setup for SESANS with adiabatic/RF flippers in magnets, existing at PNPI. The final polarisation of a divergent “ribbon beam” of height 2 cm is calculated as a function of λ. For λ= 6 A, flippers 56 cm apart and RF frequency 1 MHz we find spin-echo length δ= 0.9 μm. We show numerically, how λ is converted to δ. Extension to δ= 20 μm is realistic.
...
We made software to simulate Larmor precession in a setup for SESANS with adiabatic/RF flippers in magnets, existing at PNPI. The final polarisation of a divergent “ribbon beam” of height 2 cm is calculated as a function of λ. For λ= 6 A, flippers 56 cm apart and RF frequency 1 MHz we find spin-echo length δ= 0.9 μm. We show numerically, how λ is converted to δ. Extension to δ= 20 μm is realistic.
The use of π-flippers for correction of line integrals in Larmor-precession devices is described. The π-flippersconsist of magnetised foils of the proper thickness, magnetised by the field of the precession device itself. Application of such π-flippers in a spin-echo small angle neutron scattering set-up with fields perpendicular and parallel to the beam direction is discussed. It appears that such flippers avoid corrections for the inhomogeneity of the field-line integrals, for the main part, in both options.
...
The use of π-flippers for correction of line integrals in Larmor-precession devices is described. The π-flippersconsist of magnetised foils of the proper thickness, magnetised by the field of the precession device itself. Application of such π-flippers in a spin-echo small angle neutron scattering set-up with fields perpendicular and parallel to the beam direction is discussed. It appears that such flippers avoid corrections for the inhomogeneity of the field-line integrals, for the main part, in both options.
Larmor-precession devices need homogeneous line integrals of the magnetic field along the neutron trajectories over the beam cross section. Line-integral inhomogeneities must be homogenized or corrected in order not to spoil the initial polarization. They can be corrected by two sets of coils. The first set of coils generates a vertical field gradient opposite to the precession-field gradient. Actually, these coils transform a gradient of the line integral in the field direction to a direction perpendicular to it. This last gradient is corrected by the second set of coils, which has a homogenous field in the vertical direction and a parabolic shape in the perpendicular direction. The corrected beam has a polarization of 0.82 for a beam cross section of 10×15 mm2 whereas, for the uncorrected beam, the polarization is 0.20.
...
Larmor-precession devices need homogeneous line integrals of the magnetic field along the neutron trajectories over the beam cross section. Line-integral inhomogeneities must be homogenized or corrected in order not to spoil the initial polarization. They can be corrected by two sets of coils. The first set of coils generates a vertical field gradient opposite to the precession-field gradient. Actually, these coils transform a gradient of the line integral in the field direction to a direction perpendicular to it. This last gradient is corrected by the second set of coils, which has a homogenous field in the vertical direction and a parabolic shape in the perpendicular direction. The corrected beam has a polarization of 0.82 for a beam cross section of 10×15 mm2 whereas, for the uncorrected beam, the polarization is 0.20.
Journal article
(2002)
-
W. G. Bouwman, O. Uca, S. V. Grigoriev, W. H. Kraan, J. Plomp, M. T. Rekveldt
Spin-echo small-angle neutron scattering of dilute dispersions of mono-disperse polystyrene spheres is measured. The spheres have radii of 60 and 100 nm. The measurements agree well in shape and absolute intensity with calculations. Multiple scattering is significant in these experiments and is easily taken into account. This is the first time that quantitative analysis of real-space small-angle neutron scattering is possible. The calculations show that this technique will have most applications in systems with strong scattering, which usually implies larger length scales.
...
Spin-echo small-angle neutron scattering of dilute dispersions of mono-disperse polystyrene spheres is measured. The spheres have radii of 60 and 100 nm. The measurements agree well in shape and absolute intensity with calculations. Multiple scattering is significant in these experiments and is easily taken into account. This is the first time that quantitative analysis of real-space small-angle neutron scattering is possible. The calculations show that this technique will have most applications in systems with strong scattering, which usually implies larger length scales.
Journal article
(2002)
-
M. T. Rekveldt, W. G. Bouwman, W. H. Kraan, S. V. Grigoriev, O. Uca, T. Keller
Larmor precession has been used in the past in neutron spin-echo and neutron depolarisation. In the last decade, interest has been revived in the inclined front and end faces of the precession regions combined with the neutron-resonance spin-echo (NRSE) technique. Various techniques based on these inclined faces have been developed, such as spin-echo, small-angle neutron scattering (SESANS), off-specular neutron reflectometry using SESANS and high-resolution diffraction using Larmor precession. An overview will be given of the various state-of-the-art techniques.
...
Larmor precession has been used in the past in neutron spin-echo and neutron depolarisation. In the last decade, interest has been revived in the inclined front and end faces of the precession regions combined with the neutron-resonance spin-echo (NRSE) technique. Various techniques based on these inclined faces have been developed, such as spin-echo, small-angle neutron scattering (SESANS), off-specular neutron reflectometry using SESANS and high-resolution diffraction using Larmor precession. An overview will be given of the various state-of-the-art techniques.
Journal article
(1993)
-
P. I. Mayo, K. O'Grady, P. Sollis, P. R. Bissell, R. G. Gilson, R. W. Chantrell, A. R. Balkenende, M. Th Rekveldt, W. Kraan, P. T. Por
A detailed study of the magnetic behaviour of CrO2 dispersions is described. The study includes static and dynamic measurements and also some preliminary results on the structure of the dispersion obtained by Neutron Depolarisation which was carried out in an attempt to determine the long-range order in the dispersion. The measurements are interpreted in terms of a simple model of the evolution of dispersion quality during the milling process. Magnetic measurements are shown to be useful in characterising dispersion quality although a number of techniques are required in order to probe different aspects of dispersion behaviour.
...
A detailed study of the magnetic behaviour of CrO2 dispersions is described. The study includes static and dynamic measurements and also some preliminary results on the structure of the dispersion obtained by Neutron Depolarisation which was carried out in an attempt to determine the long-range order in the dispersion. The measurements are interpreted in terms of a simple model of the evolution of dispersion quality during the milling process. Magnetic measurements are shown to be useful in characterising dispersion quality although a number of techniques are required in order to probe different aspects of dispersion behaviour.