4.3.1.10. NXcrystal¶
Status:
base class, extends NXobject
Description:
A crystal monochromator or analyzer.
Permits double bent monochromator comprised of multiple segments with anisotropic Gaussian mosaic.
If curvatures are set to zero or are absent, array is considered to be flat.
Scattering vector is perpendicular to surface. Crystal is oriented parallel to beam incident on crystal before rotation, and lies in vertical plane.
Symbols:
These symbols will be used below to coordinate dimensions with the same lengths.
n_comp: number of different unit cells to be described
i: number of wavelengths
- Groups cited:
NXdata, NXgeometry, NXlog, NXoff_geometry, NXshape, NXtransformations
Structure:
@default: (optional) NX_CHAR
Declares which child group contains a path leading to a NXdata group.
It is recommended (as of NIAC2014) to use this attribute to help define the path to the default dataset to be plotted. See https://www.nexusformat.org/2014_How_to_find_default_data.html for a summary of the discussion.
usage: (optional) NX_CHAR
How this crystal is used. Choices are in the list.
Any of these values:
Bragg: reflection geometry
Laue: The chemical formula specified using CIF conventions. Abbreviated version of CIF standard: * Only recognized element symbols may be used. * Each element symbol is followed by a ‘count’ number. A count of ‘1’ may be omitted. * A space or parenthesis must separate each cluster of (element symbol + count). * Where a group of elements is enclosed in parentheses, the multiplier for the group must follow the closing parentheses. That is, all element and group multipliers are assumed to be printed as subscripted numbers. * Unless the elements are ordered in a manner that corresponds to their chemical structure, the order of the elements within any group or moiety depends on whether or not carbon is present. * If carbon is present, the order should be: C, then H, then the other elements in alphabetical order of their symbol. If carbon is not present, the elements are listed purely in alphabetic order of their symbol. This is the Hill system used by Chemical Abstracts. See, for example: http://www.iucr.org/__data/iucr/cif/standard/cifstd15.html or http://www.cas.org/training/stneasytips/subinforformula1.html.type: (optional) NX_CHAR
Type or material of monochromating substance. Chemical formula can be specified separately. Use the “reflection” field to indicate the (hkl) orientation. Use the “d_spacing” field to record the lattice plane spacing.
This field was changed (2010-11-17) from an enumeration to a string since common usage showed a wider variety of use than a simple list. These are the items in the list at the time of the change: PG (Highly Oriented Pyrolytic Graphite) | Ge | Si | Cu | Fe3Si | CoFe | Cu2MnAl (Heusler) | Multilayer | Diamond.
chemical_formula: (optional) NX_CHAR
The chemical formula specified using CIF conventions. Abbreviated version of CIF standard:
Only recognized element symbols may be used.
Each element symbol is followed by a ‘count’ number. A count of ‘1’ may be omitted.
A space or parenthesis must separate each cluster of (element symbol + count).
Where a group of elements is enclosed in parentheses, the multiplier for the group must follow the closing parentheses. That is, all element and group multipliers are assumed to be printed as subscripted numbers.
Unless the elements are ordered in a manner that corresponds to their chemical structure, the order of the elements within any group or moiety depends on whether or not carbon is present.
If carbon is present, the order should be: C, then H, then the other elements in alphabetical order of their symbol. If carbon is not present, the elements are listed purely in alphabetic order of their symbol.
This is the Hill system used by Chemical Abstracts.
order_no: (optional) NX_INT
A number which describes if this is the first, second,.. \(n^{th}\) crystal in a multi crystal monochromator
cut_angle: (optional) NX_FLOAT {units=NX_ANGLE}
Cut angle of reflecting Bragg plane and plane of crystal surface
space_group: (optional) NX_CHAR
Space group of crystal structure
unit_cell: (optional) NX_FLOAT (Rank: 2, Dimensions: [n_comp, 6]) {units=NX_LENGTH}
Unit cell parameters (lengths and angles)
unit_cell_a: (optional) NX_FLOAT {units=NX_LENGTH}
Unit cell lattice parameter: length of side a
unit_cell_b: (optional) NX_FLOAT {units=NX_LENGTH}
Unit cell lattice parameter: length of side b
unit_cell_c: (optional) NX_FLOAT {units=NX_LENGTH}
Unit cell lattice parameter: length of side c
unit_cell_alpha: (optional) NX_FLOAT {units=NX_ANGLE}
Unit cell lattice parameter: angle alpha
unit_cell_beta: (optional) NX_FLOAT {units=NX_ANGLE}
Unit cell lattice parameter: angle beta
unit_cell_gamma: (optional) NX_FLOAT {units=NX_ANGLE}
Unit cell lattice parameter: angle gamma
unit_cell_volume: (optional) NX_FLOAT {units=NX_VOLUME}
Volume of the unit cell
orientation_matrix: (optional) NX_FLOAT (Rank: 2, Dimensions: [3, 3])
Orientation matrix of single crystal sample using Busing-Levy convention: W. R. Busing and H. A. Levy (1967). Acta Cryst. 22, 457-464
wavelength: (optional) NX_FLOAT (Rank: 1, Dimensions: [i]) {units=NX_WAVELENGTH}
Optimum diffracted wavelength
d_spacing: (optional) NX_FLOAT {units=NX_LENGTH}
spacing between crystal planes of the reflection
scattering_vector: (optional) NX_FLOAT {units=NX_WAVENUMBER}
Scattering vector, Q, of nominal reflection
reflection: (optional) NX_INT (Rank: 1, Dimensions: [3]) {units=NX_UNITLESS}
Miller indices (hkl) values of nominal reflection
thickness: (optional) NX_FLOAT {units=NX_LENGTH}
Thickness of the crystal. (Required for Laue orientations - see “usage” field)
density: (optional) NX_NUMBER {units=NX_MASS_DENSITY}
mass density of the crystal
segment_width: (optional) NX_FLOAT {units=NX_LENGTH}
Horizontal width of individual segment
segment_height: (optional) NX_FLOAT {units=NX_LENGTH}
Vertical height of individual segment
segment_thickness: (optional) NX_FLOAT {units=NX_LENGTH}
Thickness of individual segment
segment_gap: (optional) NX_FLOAT {units=NX_LENGTH}
Typical gap between adjacent segments
segment_columns: (optional) NX_FLOAT {units=NX_LENGTH}
number of segment columns in horizontal direction
segment_rows: (optional) NX_FLOAT {units=NX_LENGTH}
number of segment rows in vertical direction
mosaic_horizontal: (optional) NX_FLOAT {units=NX_ANGLE}
horizontal mosaic Full Width Half Maximum
mosaic_vertical: (optional) NX_FLOAT {units=NX_ANGLE}
vertical mosaic Full Width Half Maximum
curvature_horizontal: (optional) NX_FLOAT {units=NX_ANGLE}
Horizontal curvature of focusing crystal
curvature_vertical: (optional) NX_FLOAT {units=NX_ANGLE}
Vertical curvature of focusing crystal
is_cylindrical: (optional) NX_BOOLEAN
Is this crystal bent cylindrically?
cylindrical_orientation_angle: (optional) NX_NUMBER {units=NX_ANGLE}
If cylindrical: cylinder orientation angle
polar_angle: (optional) NX_FLOAT (Rank: 1, Dimensions: [i]) {units=NX_ANGLE}
Polar (scattering) angle at which crystal assembly is positioned. Note: some instrument geometries call this term 2theta. Note: it is recommended to use NXtransformations instead.
azimuthal_angle: (optional) NX_FLOAT (Rank: 1, Dimensions: [i]) {units=NX_ANGLE}
Azimuthal angle at which crystal assembly is positioned. Note: it is recommended to use NXtransformations instead.
bragg_angle: (optional) NX_FLOAT (Rank: 1, Dimensions: [i]) {units=NX_ANGLE}
Bragg angle of nominal reflection
temperature: (optional) NX_FLOAT {units=NX_TEMPERATURE}
average/nominal crystal temperature
temperature_coefficient: (optional) NX_FLOAT {units=NX_ANY}
how lattice parameter changes with temperature
depends_on: (optional) NX_CHAR
NeXus positions components by applying a set of translations and rotations to apply to the component starting from 0, 0, 0. The order of these operations is critical and forms what NeXus calls a dependency chain. The depends_on field defines the path to the top most operation of the dependency chain or the string “.” if located in the origin. Usually these operations are stored in a NXtransformations group. But NeXus allows them to be stored anywhere.
GEOMETRY: (optional) NXgeometry
DEPRECATED: Use the field depends_on and NXtransformations to position the crystal and NXoff_geometry to describe its shape instead
Position of crystal
temperature_log: (optional) NXlog
log file of crystal temperature
reflectivity: (optional) NXdata
crystal reflectivity versus wavelength
transmission: (optional) NXdata
crystal transmission versus wavelength
shape: (optional) NXshape
DEPRECATED: Use NXoff_geometry instead to describe the shape of the monochromator
A NXshape group describing the shape of the crystal arrangement
OFF_GEOMETRY: (optional) NXoff_geometry
This group describes the shape of the beam line component
TRANSFORMATIONS: (optional) NXtransformations
Transformations used by this component to define its position and orientation.
Hypertext Anchors¶
List of hypertext anchors for all groups, fields, attributes, and links defined in this class.