Scan profiles for neutron spectrometers. I. Gaussian-profile elements by acceptance-diagram methods

2003 ◽  
Vol 36 (5) ◽  
pp. 1204-1213 ◽  
Author(s):  
L. D. Cussen
Keyword(s):  
Neutron Scattering ◽  
Graphical Method ◽  
Beam Elements ◽  
Gaussian Profile ◽  
Rectangular Profile ◽  
Beam Characteristics

`Acceptance diagrams' are a powerful graphical method of describing beam characteristics on neutron scattering instruments. Recent examples of the technique have used hypothetical rectangular-profile beam elements, not the conventional Gaussian profiles, to clarify the description. This article develops the method for Gaussian-profile beam elements and shows that it gives identical results to accepted techniques. Direct expressions are presented for scan profiles, their widths and intensities for both powder diffractometers and three-axis spectrometers. This work gives some necessary background and therefore forms the first part of a discussion of the resolution effects of the new reflecting Soller collimators for neutrons.

Scan profiles for neutron spectrometers. II. Rectangular-profile elements by acceptance-diagram methods

2003 ◽  
Vol 36 (5) ◽  
pp. 1214-1224
Author(s):  
L. D. Cussen
Keyword(s):  
Neutron Scattering ◽  
Angular Spread ◽  
Significant Gain ◽  
Angular Divergence ◽  
Rectangular Profile ◽  
Effective Use ◽  
Extended View

The recent development of neutron collimators with rectangular transmission profiles (intensityversusangular divergence) extends hope of improved count rates on neutron scattering instruments. It is usually assumed that a more effective use of beam angular spread in these devices should increase count rates by about a factor of two. However, real beams have both angular and wavevector spread and both these spreads are governed by the allowed collimation. In this extended view, the gains from ideal rectangular-profile elements (angle filters) are shown to be much larger (about a factor of four). The mirror reflections used to achieve the rectangular profiles in real devices complicate the resolution effects. Specifically, the reflections disturb the wavevector–angular divergence correlation in the beams, leading to unusual peak shapes characterized by triple peaks on powder diffractometers. Thus, these reflecting collimators are likely to be universally useful only before the monochromator and immediately preceding the detector, where wavevector–angle correlations have no effect. This reduces the potential gains to a factor of two or so. Note that the gains are as previously expected but for quite different reasons than imagined. This remains a very significant gain in a field where most work is intensity-limited.

An acceptance-diagram description of beams from focusing monochromators

2002 ◽  
Vol 35 (6) ◽  
pp. 702-712 ◽  
Author(s):  
L. D. Cussen
Keyword(s):  
Inelastic Scattering ◽  
Neutron Scattering ◽  
Single Crystal ◽  
Graphical Method ◽  
Neutron Guide ◽  
Guide Tube ◽  
Signal To Noise ◽  
Kinematic Approximation ◽  
Spatial Dimensions

`Acceptance' diagrams are used to describe the beams produced by curved segmented (`focusing') monochromators in the kinematic approximation. This semi-analytic semi-graphical method leads to a complete description which is readily visualized in terms of instrument variables. Focusing both in and perpendicular to the scattering plane is considered. Clear relationships are identified between instrument dimensions and the beam produced. The description is directed towards neutron scattering instruments but the formalism should also apply to photons and electrons. It is demonstrated that a monochromator curved both in and perpendicular to the scattering plane (`double focused') on either a straight or curved neutron guide tube from a reactor source can produce a beam of comparable flux to that achievable at the reactor face. Such a beam has spatial dimensions comparable with modern single-crystal samples for inelastic scattering and could thus provide spectacular signal and, even more interestingly, signal to noise ratios for both elastic and inelastic single-crystal spectrometers.

Resolution of neutron three-axis spectrometers using acceptance diagrams

2002 ◽  
Vol 35 (5) ◽  
pp. 615-623 ◽  
Author(s):  
L. D. Cussen
Keyword(s):  
Inelastic Scattering ◽  
Transmission Function ◽  
Two Dimensional ◽  
Beam Elements ◽  
Gaussian Profile

Two-dimensional `acceptance diagrams' are used to discuss the transmission function and the resolution of neutron three-axis spectrometers. The discussion is simplified by assuming rectangular rather than the usual Gaussian transmission profiles for the beam elements,i.e.collimators and crystal mosaic spreads, but the results can be applied to the Gaussian profile approximation. The formalism clearly shows the effects of beam elements on the instrument transmission to the detector. Suitable choices of beam elements are determined to match the transmission functions of the primary and secondary spectrometers and hence optimize measurements. The effect of sample mosaic is addressed. The `focusing angle' for inelastic scattering is determined and discussed.

Study of the Bending Stiffness and Cable Characteristics of Tension Components

2012 ◽  
Vol 188 ◽  
pp. 17-24
Author(s):  
Mao Lin Tang ◽  
Ya Guang Du ◽  
Rui Li Shen ◽  
Kun Yan
Keyword(s):  
Computing Time ◽  
Characteristic Parameter ◽  
Bending Stiffness ◽  
Geometric Shape ◽  
Element Analysis ◽  
Hollow Beam ◽  
Cable Structure ◽  
Beam Elements ◽  
Calculation Results ◽  
Beam Characteristics

To study the behavior changing between cable characteristics and beam characteristics, the geometric shape calculation formulae for tension components with bending stiffness are derived from ones with the boundary conditions of two ends hinged, one hinged joint and the other fixed and two ends fixed respectively. Then, using the concept of tension stiffness, the effects of Cable Characteristic Parameter on the geometric shape of tension components are studied. Analyses indicate that with the increase in the value of the Cable Characteristic Parameter, the cable characteristics of components become more obvious. That is, a bar with enormous tension can be calculated as a cable element even if its bending stiffness is large. In structure finite element analysis, more storage space and computing time could be saved as long as components are simplified with cable elements other than beam elements, the simplification should be carried out basing on the Cable Characteristic Parameter. Calculation results on a hollow beam verify that when tension increases, components’ mechanical properties gradually change from beam characteristics to cable characteristics and eventually they tend to be identical with the theoretical calculation of cable structure.

On the resolution of neutron scattering instruments

2000 ◽  
Vol 33 (6) ◽  
pp. 1399-1404 ◽  
Author(s):  
Leo D. Cussen
Keyword(s):  
Phase Space ◽  
Neutron Scattering ◽  
Usual Practice ◽  
Beam Elements ◽  
Powder Samples

Phase-space arguments are used to discuss the resolution of neutron scattering instruments. The usual practice in such studies is to assume that all beam elements have Gaussian profiles. Here, the assumption that all elements have rectangular profiles results in considerable clarification of the role of each instrument component. The discussion is limited to powder diffractometers and powder samples on three-axis spectrometers, but it is possible to use the results when considering more involved measurements. The choice of collimators and monochromator mosaic to optimize measurements is discussed. The assumption of rectangular elements is not entirely artificial, as it is now possible to build such components. Furthermore, the conclusions can be applied to instruments with Gaussian elements.

Resolution calculations for novel neutron beam elements

2000 ◽  
Vol 33 (6) ◽  
pp. 1393-1398 ◽  
Author(s):  
Leo D. Cussen
Keyword(s):  
Phase Space ◽  
Neutron Beam ◽  
Lattice Spacing ◽  
Teaching Tool ◽  
Optical Elements ◽  
Beam Elements ◽  
Neutron Beams ◽  
Rectangular Profile ◽  
Phase Space Methods

It is now possible to build new types of optical elements for neutron beams. These include monochromating crystals with rectangular mosaic profiles, `gradient' monochromating crystals with varying lattice spacing, and collimators with rectangular profiles. Phase-space methods are used to describe the resolution of a combination of two collimators and a monochromating crystal for various combinations of novel beam elements. The description of rectangular-profile elements in this formalism considerably simplifies the normal description of resolution effects and should thus prove useful as a teaching tool.

Local atomic structure of relaxor ferroelectric solids studied by pulsed neutron scattering

1994 ◽  
Vol 52 ◽  
pp. 554-555
Author(s):  
T. Egami ◽  
H. D. Rosenfeld ◽  
S. Teslic
Keyword(s):  
Neutron Scattering ◽  
Atomic Structure ◽  
Argonne National Laboratory ◽  
Relaxor Ferroelectrics ◽  
Relaxor Ferroelectric ◽  
Crystallographic Structure ◽  
Chemical Inhomogeneity ◽  
Distribution Analysis ◽  
Ferroelectric Transition ◽  
Pulsed Neutron

Relaxor ferroelectrics, such as Pb(Mg1/3Nb2/3)O3 (PMN) or (Pb·88La ·12)(Zr·65Ti·35)O3 (PLZT), show diffuse ferroelectric transition which depends upon frequency of the a.c. field. In spite of their wide use in various applications details of their atomic structure and the mechanism of relaxor ferroelectric transition are not sufficiently understood. While their crystallographic structure is cubic perovskite, ABO3, their thermal factors (apparent amplitude of thermal vibration) is quite large, suggesting local displacive disorder due to heterovalent ion mixing. Electron microscopy suggests nano-scale structural as well as chemical inhomogeneity.We have studied the atomic structure of these solids by pulsed neutron scattering using the atomic pair-distribution analysis. The measurements were made at the Intense Pulsed Neutron Source (IPNS) of Argonne National Laboratory. Pulsed neutrons are produced by a pulsed proton beam accelerated to 750 MeV hitting a uranium target at a rate of 30 Hz. Even after moderation by a liquid methane moderator high flux of epithermal neutrons with energies ranging up to few eV’s remain.

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