These symbols will be used below to coordinate dimensions with the same lengths. number of different unit cells to be described number of wavelengths 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. Position of crystal How this crystal is used. Choices are in the list. reflection geometry 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 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. 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. A number which describes if this is the first, second,.. :math:`n^{th}` crystal in a multi crystal monochromator Cut angle of reflecting Bragg plane and plane of crystal surface Space group of crystal structure Unit cell parameters (lengths and angles) Unit cell lattice parameter: length of side a Unit cell lattice parameter: length of side b Unit cell lattice parameter: length of side c Unit cell lattice parameter: angle alpha Unit cell lattice parameter: angle beta Unit cell lattice parameter: angle gamma Volume of the unit cell Orientation matrix of single crystal sample using Busing-Levy convention: W. R. Busing and H. A. Levy (1967). Acta Cryst. 22, 457-464 Optimum diffracted wavelength spacing between crystal planes of the reflection Scattering vector, Q, of nominal reflection Miller indices (hkl) values of nominal reflection Thickness of the crystal. (Required for Laue orientations - see "usage" field) mass density of the crystal Horizontal width of individual segment Vertical height of individual segment Thickness of individual segment Typical gap between adjacent segments number of segment columns in horizontal direction number of segment rows in vertical direction horizontal mosaic Full Width Half Maximum vertical mosaic Full Width Half Maximum Horizontal curvature of focusing crystal Vertical curvature of focusing crystal Is this crystal bent cylindrically? If cylindrical: cylinder orientation angle Polar (scattering) angle at which crystal assembly is positioned. Note: some instrument geometries call this term 2theta. Azimuthal angle at which crystal assembly is positioned Bragg angle of nominal reflection average/nominal crystal temperature how lattice parameter changes with temperature log file of crystal temperature crystal reflectivity versus wavelength crystal transmission versus wavelength A NXshape group describing the shape of the crystal arrangement