.. auto-generated by dev_tools.docs.nxdl from the NXDL source base_classes/NXcrystal.nxdl.xml -- DO NOT EDIT

.. index::
    ! NXcrystal (base class)
    ! crystal (base class)
    see: crystal (base class); NXcrystal

.. _NXcrystal:

=========
NXcrystal
=========

..
    Contributors List

    .. |contrib_name| replace:: Aaron Brewster|phyy-nx|https://avatars.githubusercontent.com/u/13471434?v=4|2022-06-15

    .. |contrib_name| replace:: Pete R Jemian|prjemian|https://avatars.githubusercontent.com/u/2279984?v=4|2022-01-28

    .. |contrib_name| replace:: Peter Chang|PeterC-DLS|https://avatars.githubusercontent.com/u/1381719?v=4|2020-10-20

    .. |contrib_name| replace:: Freddie Akeroyd|FreddieAkeroyd|https://avatars.githubusercontent.com/u/1132753?v=4|2020-01-23

    .. |contrib_name| replace:: Tobias Richter|zjttoefs|https://avatars.githubusercontent.com/u/856440?v=4|2018-05-15

    .. |contrib_name| replace:: Joachim Wuttke (o)|jwuttke|https://avatars.githubusercontent.com/u/5262000?v=4|2014-09-02

**Status**:

  base class, extends :ref:`NXobject`

**Description**:

  .. collapse:: A crystal monochromator or analyzer. ...

      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**:
  :ref:`NXdata`, :ref:`NXgeometry`, :ref:`NXlog`, :ref:`NXoff_geometry`, :ref:`NXshape`, :ref:`NXtransformations`

.. index:: NXgeometry (base class); used in base class, NXlog (base class); used in base class, NXdata (base class); used in base class, NXshape (base class); used in base class, NXoff_geometry (base class); used in base class, NXtransformations (base class); used in base class

**Structure**:

  .. _/NXcrystal@default-attribute:

  .. index:: default (file attribute)

  **@default**: (optional) :ref:`NX_CHAR <NX_CHAR>` 

    .. collapse:: Declares which child group contains a path leading  ...

        .. index:: plotting

        Declares which child group contains a path leading 
        to a :ref:`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.

  .. _/NXcrystal/usage-field:

  .. index:: usage (field)

  **usage**: (optional) :ref:`NX_CHAR <NX_CHAR>` 

    .. collapse:: How this crystal is used.  Choices are in the list. ...

        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.


  .. _/NXcrystal/type-field:

  .. index:: type (field)

  **type**: (optional) :ref:`NX_CHAR <NX_CHAR>` 

    .. collapse:: Type or material of monochromating substance.   ...

        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.

  .. _/NXcrystal/chemical_formula-field:

  .. index:: chemical_formula (field)

  **chemical_formula**: (optional) :ref:`NX_CHAR <NX_CHAR>` 

    .. collapse:: The chemical formula specified using CIF conventions. ...

        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.

  .. _/NXcrystal/order_no-field:

  .. index:: order_no (field)

  **order_no**: (optional) :ref:`NX_INT <NX_INT>` 

    .. collapse:: A number which describes if this is the first, second,..  ...

        A number which describes if this is the first, second,.. 
        :math:`n^{th}` crystal in a multi crystal monochromator

  .. _/NXcrystal/cut_angle-field:

  .. index:: cut_angle (field)

  **cut_angle**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` {units=\ :ref:`NX_ANGLE <NX_ANGLE>`} 

    Cut angle of reflecting Bragg plane and plane of crystal surface

  .. _/NXcrystal/space_group-field:

  .. index:: space_group (field)

  **space_group**: (optional) :ref:`NX_CHAR <NX_CHAR>` 

    Space group of crystal structure

  .. _/NXcrystal/unit_cell-field:

  .. index:: unit_cell (field)

  **unit_cell**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` (Rank: 2, Dimensions: [n_comp, 6]) {units=\ :ref:`NX_LENGTH <NX_LENGTH>`} 

    Unit cell parameters (lengths and angles)

  .. _/NXcrystal/unit_cell_a-field:

  .. index:: unit_cell_a (field)

  **unit_cell_a**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` {units=\ :ref:`NX_LENGTH <NX_LENGTH>`} 

    Unit cell lattice parameter: length of side a

  .. _/NXcrystal/unit_cell_b-field:

  .. index:: unit_cell_b (field)

  **unit_cell_b**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` {units=\ :ref:`NX_LENGTH <NX_LENGTH>`} 

    Unit cell lattice parameter: length of side b

  .. _/NXcrystal/unit_cell_c-field:

  .. index:: unit_cell_c (field)

  **unit_cell_c**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` {units=\ :ref:`NX_LENGTH <NX_LENGTH>`} 

    Unit cell lattice parameter: length of side c

  .. _/NXcrystal/unit_cell_alpha-field:

  .. index:: unit_cell_alpha (field)

  **unit_cell_alpha**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` {units=\ :ref:`NX_ANGLE <NX_ANGLE>`} 

    Unit cell lattice parameter: angle alpha

  .. _/NXcrystal/unit_cell_beta-field:

  .. index:: unit_cell_beta (field)

  **unit_cell_beta**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` {units=\ :ref:`NX_ANGLE <NX_ANGLE>`} 

    Unit cell lattice parameter: angle beta

  .. _/NXcrystal/unit_cell_gamma-field:

  .. index:: unit_cell_gamma (field)

  **unit_cell_gamma**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` {units=\ :ref:`NX_ANGLE <NX_ANGLE>`} 

    Unit cell lattice parameter: angle gamma

  .. _/NXcrystal/unit_cell_volume-field:

  .. index:: unit_cell_volume (field)

  **unit_cell_volume**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` {units=\ :ref:`NX_VOLUME <NX_VOLUME>`} 

    Volume of the unit cell

  .. _/NXcrystal/orientation_matrix-field:

  .. index:: orientation_matrix (field)

  **orientation_matrix**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` (Rank: 2, Dimensions: [3, 3]) 

    .. collapse:: Orientation matrix of single crystal sample using Busing-Levy convention: ...

        Orientation matrix of single crystal sample using Busing-Levy convention:
        W. R. Busing and H. A. Levy (1967). Acta Cryst. 22, 457-464

  .. _/NXcrystal/wavelength-field:

  .. index:: wavelength (field)

  **wavelength**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` (Rank: 1, Dimensions: [i]) {units=\ :ref:`NX_WAVELENGTH <NX_WAVELENGTH>`} 

    Optimum diffracted wavelength

  .. _/NXcrystal/d_spacing-field:

  .. index:: d_spacing (field)

  **d_spacing**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` {units=\ :ref:`NX_LENGTH <NX_LENGTH>`} 

    spacing between crystal planes of the reflection

  .. _/NXcrystal/scattering_vector-field:

  .. index:: scattering_vector (field)

  **scattering_vector**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` {units=\ :ref:`NX_WAVENUMBER <NX_WAVENUMBER>`} 

    Scattering vector, Q, of nominal reflection

  .. _/NXcrystal/reflection-field:

  .. index:: reflection (field)

  **reflection**: (optional) :ref:`NX_INT <NX_INT>` (Rank: 1, Dimensions: [3]) {units=\ :ref:`NX_UNITLESS <NX_UNITLESS>`} 

    Miller indices (hkl) values of nominal reflection

  .. _/NXcrystal/thickness-field:

  .. index:: thickness (field)

  **thickness**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` {units=\ :ref:`NX_LENGTH <NX_LENGTH>`} 

    Thickness of the crystal.  (Required for Laue orientations - see "usage" field)

  .. _/NXcrystal/density-field:

  .. index:: density (field)

  **density**: (optional) :ref:`NX_NUMBER <NX_NUMBER>` {units=\ :ref:`NX_MASS_DENSITY <NX_MASS_DENSITY>`} 

    mass density of the crystal

  .. _/NXcrystal/segment_width-field:

  .. index:: segment_width (field)

  **segment_width**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` {units=\ :ref:`NX_LENGTH <NX_LENGTH>`} 

    Horizontal width of individual segment

  .. _/NXcrystal/segment_height-field:

  .. index:: segment_height (field)

  **segment_height**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` {units=\ :ref:`NX_LENGTH <NX_LENGTH>`} 

    Vertical height of individual segment

  .. _/NXcrystal/segment_thickness-field:

  .. index:: segment_thickness (field)

  **segment_thickness**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` {units=\ :ref:`NX_LENGTH <NX_LENGTH>`} 

    Thickness of individual segment

  .. _/NXcrystal/segment_gap-field:

  .. index:: segment_gap (field)

  **segment_gap**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` {units=\ :ref:`NX_LENGTH <NX_LENGTH>`} 

    Typical gap between adjacent segments

  .. _/NXcrystal/segment_columns-field:

  .. index:: segment_columns (field)

  **segment_columns**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` {units=\ :ref:`NX_LENGTH <NX_LENGTH>`} 

    number of segment columns in horizontal direction

  .. _/NXcrystal/segment_rows-field:

  .. index:: segment_rows (field)

  **segment_rows**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` {units=\ :ref:`NX_LENGTH <NX_LENGTH>`} 

    number of segment rows in vertical direction

  .. _/NXcrystal/mosaic_horizontal-field:

  .. index:: mosaic_horizontal (field)

  **mosaic_horizontal**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` {units=\ :ref:`NX_ANGLE <NX_ANGLE>`} 

    horizontal mosaic Full Width Half Maximum

  .. _/NXcrystal/mosaic_vertical-field:

  .. index:: mosaic_vertical (field)

  **mosaic_vertical**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` {units=\ :ref:`NX_ANGLE <NX_ANGLE>`} 

    vertical mosaic Full Width Half Maximum

  .. _/NXcrystal/curvature_horizontal-field:

  .. index:: curvature_horizontal (field)

  **curvature_horizontal**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` {units=\ :ref:`NX_ANGLE <NX_ANGLE>`} 

    Horizontal curvature of focusing crystal

  .. _/NXcrystal/curvature_vertical-field:

  .. index:: curvature_vertical (field)

  **curvature_vertical**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` {units=\ :ref:`NX_ANGLE <NX_ANGLE>`} 

    Vertical curvature of focusing crystal

  .. _/NXcrystal/is_cylindrical-field:

  .. index:: is_cylindrical (field)

  **is_cylindrical**: (optional) :ref:`NX_BOOLEAN <NX_BOOLEAN>` 

    Is this crystal bent cylindrically?

  .. _/NXcrystal/cylindrical_orientation_angle-field:

  .. index:: cylindrical_orientation_angle (field)

  **cylindrical_orientation_angle**: (optional) :ref:`NX_NUMBER <NX_NUMBER>` {units=\ :ref:`NX_ANGLE <NX_ANGLE>`} 

    If cylindrical: cylinder orientation angle

  .. _/NXcrystal/polar_angle-field:

  .. index:: polar_angle (field)

  **polar_angle**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` (Rank: 1, Dimensions: [i]) {units=\ :ref:`NX_ANGLE <NX_ANGLE>`} 

    .. collapse:: Polar (scattering) angle at which crystal assembly is positioned.   ...

        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.

  .. _/NXcrystal/azimuthal_angle-field:

  .. index:: azimuthal_angle (field)

  **azimuthal_angle**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` (Rank: 1, Dimensions: [i]) {units=\ :ref:`NX_ANGLE <NX_ANGLE>`} 

    .. collapse:: Azimuthal angle at which crystal assembly is positioned. ...

        Azimuthal angle at which crystal assembly is positioned.
        Note: it is recommended to use NXtransformations instead.

  .. _/NXcrystal/bragg_angle-field:

  .. index:: bragg_angle (field)

  **bragg_angle**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` (Rank: 1, Dimensions: [i]) {units=\ :ref:`NX_ANGLE <NX_ANGLE>`} 

    Bragg angle of nominal reflection

  .. _/NXcrystal/temperature-field:

  .. index:: temperature (field)

  **temperature**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` {units=\ :ref:`NX_TEMPERATURE <NX_TEMPERATURE>`} 

    average/nominal crystal temperature

  .. _/NXcrystal/temperature_coefficient-field:

  .. index:: temperature_coefficient (field)

  **temperature_coefficient**: (optional) :ref:`NX_FLOAT <NX_FLOAT>` {units=\ :ref:`NX_ANY <NX_ANY>`} 

    how lattice parameter changes with temperature

  .. _/NXcrystal/depends_on-field:

  .. index:: depends_on (field)

  **depends_on**: (optional) :ref:`NX_CHAR <NX_CHAR>` 

    .. collapse:: NeXus positions components by applying a set of translations and rotations ...

        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.

        .. todo::
          Add a definition for the reference point of a crystal.

  .. _/NXcrystal/GEOMETRY-group:

  **GEOMETRY**: (optional) :ref:`NXgeometry` 


    .. index:: deprecated


    **DEPRECATED**: Use the field `depends_on` and :ref:`NXtransformations` to position the crystal and NXoff_geometry to describe its shape instead

    Position of crystal

  .. _/NXcrystal/temperature_log-group:

  **temperature_log**: (optional) :ref:`NXlog` 

    log file of crystal temperature

  .. _/NXcrystal/reflectivity-group:

  **reflectivity**: (optional) :ref:`NXdata` 

    crystal reflectivity versus wavelength

  .. _/NXcrystal/transmission-group:

  **transmission**: (optional) :ref:`NXdata` 

    crystal transmission versus wavelength

  .. _/NXcrystal/shape-group:

  **shape**: (optional) :ref:`NXshape` 


    .. index:: deprecated


    **DEPRECATED**: Use NXoff_geometry instead to describe the shape of the monochromator

    A NXshape group describing the shape of the crystal arrangement

  .. _/NXcrystal/OFF_GEOMETRY-group:

  **OFF_GEOMETRY**: (optional) :ref:`NXoff_geometry` 

    This group describes the shape of the beam line component

  .. _/NXcrystal/TRANSFORMATIONS-group:

  **TRANSFORMATIONS**: (optional) :ref:`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.


* :ref:`/NXcrystal/azimuthal_angle-field </NXcrystal/azimuthal_angle-field>`
* :ref:`/NXcrystal/bragg_angle-field </NXcrystal/bragg_angle-field>`
* :ref:`/NXcrystal/chemical_formula-field </NXcrystal/chemical_formula-field>`
* :ref:`/NXcrystal/curvature_horizontal-field </NXcrystal/curvature_horizontal-field>`
* :ref:`/NXcrystal/curvature_vertical-field </NXcrystal/curvature_vertical-field>`
* :ref:`/NXcrystal/cut_angle-field </NXcrystal/cut_angle-field>`
* :ref:`/NXcrystal/cylindrical_orientation_angle-field </NXcrystal/cylindrical_orientation_angle-field>`
* :ref:`/NXcrystal/d_spacing-field </NXcrystal/d_spacing-field>`
* :ref:`/NXcrystal/density-field </NXcrystal/density-field>`
* :ref:`/NXcrystal/depends_on-field </NXcrystal/depends_on-field>`
* :ref:`/NXcrystal/GEOMETRY-group </NXcrystal/GEOMETRY-group>`
* :ref:`/NXcrystal/is_cylindrical-field </NXcrystal/is_cylindrical-field>`
* :ref:`/NXcrystal/mosaic_horizontal-field </NXcrystal/mosaic_horizontal-field>`
* :ref:`/NXcrystal/mosaic_vertical-field </NXcrystal/mosaic_vertical-field>`
* :ref:`/NXcrystal/OFF_GEOMETRY-group </NXcrystal/OFF_GEOMETRY-group>`
* :ref:`/NXcrystal/order_no-field </NXcrystal/order_no-field>`
* :ref:`/NXcrystal/orientation_matrix-field </NXcrystal/orientation_matrix-field>`
* :ref:`/NXcrystal/polar_angle-field </NXcrystal/polar_angle-field>`
* :ref:`/NXcrystal/reflection-field </NXcrystal/reflection-field>`
* :ref:`/NXcrystal/reflectivity-group </NXcrystal/reflectivity-group>`
* :ref:`/NXcrystal/scattering_vector-field </NXcrystal/scattering_vector-field>`
* :ref:`/NXcrystal/segment_columns-field </NXcrystal/segment_columns-field>`
* :ref:`/NXcrystal/segment_gap-field </NXcrystal/segment_gap-field>`
* :ref:`/NXcrystal/segment_height-field </NXcrystal/segment_height-field>`
* :ref:`/NXcrystal/segment_rows-field </NXcrystal/segment_rows-field>`
* :ref:`/NXcrystal/segment_thickness-field </NXcrystal/segment_thickness-field>`
* :ref:`/NXcrystal/segment_width-field </NXcrystal/segment_width-field>`
* :ref:`/NXcrystal/shape-group </NXcrystal/shape-group>`
* :ref:`/NXcrystal/space_group-field </NXcrystal/space_group-field>`
* :ref:`/NXcrystal/temperature-field </NXcrystal/temperature-field>`
* :ref:`/NXcrystal/temperature_coefficient-field </NXcrystal/temperature_coefficient-field>`
* :ref:`/NXcrystal/temperature_log-group </NXcrystal/temperature_log-group>`
* :ref:`/NXcrystal/thickness-field </NXcrystal/thickness-field>`
* :ref:`/NXcrystal/TRANSFORMATIONS-group </NXcrystal/TRANSFORMATIONS-group>`
* :ref:`/NXcrystal/transmission-group </NXcrystal/transmission-group>`
* :ref:`/NXcrystal/type-field </NXcrystal/type-field>`
* :ref:`/NXcrystal/unit_cell-field </NXcrystal/unit_cell-field>`
* :ref:`/NXcrystal/unit_cell_a-field </NXcrystal/unit_cell_a-field>`
* :ref:`/NXcrystal/unit_cell_alpha-field </NXcrystal/unit_cell_alpha-field>`
* :ref:`/NXcrystal/unit_cell_b-field </NXcrystal/unit_cell_b-field>`
* :ref:`/NXcrystal/unit_cell_beta-field </NXcrystal/unit_cell_beta-field>`
* :ref:`/NXcrystal/unit_cell_c-field </NXcrystal/unit_cell_c-field>`
* :ref:`/NXcrystal/unit_cell_gamma-field </NXcrystal/unit_cell_gamma-field>`
* :ref:`/NXcrystal/unit_cell_volume-field </NXcrystal/unit_cell_volume-field>`
* :ref:`/NXcrystal/usage-field </NXcrystal/usage-field>`
* :ref:`/NXcrystal/wavelength-field </NXcrystal/wavelength-field>`
* :ref:`/NXcrystal@default-attribute </NXcrystal@default-attribute>`

**NXDL Source**:
  https://github.com/nexusformat/definitions/blob/main/base_classes/NXcrystal.nxdl.xml