Section 3.7.4.2. The detector apparatus

Data items in these categories are as follows:

(a) DIFFRN_DETECTOR

(b) DIFFRN_DETECTOR_AXIS

(c) DIFFRN_DETECTOR_ELEMENT

The bullet () indicates a category key. The arrow () is a reference to a parent data item. Items in italics are defined in the mmCIF dictionary.

The DIFFRN_DETECTOR category is defined in the mmCIF dictionary (Section 3.6.5.2 ; see the detailed discussion in Section 3.2.2.2.4 ). The CBF/imgCIF dictionary restates the DIFFRN_DETECTOR category, adding new tags. Data items in the DIFFRN_DETECTOR category describe the detector used to measure the scattered radiation, including any analyser and post-sample collimation. In order to allow for multiple detectors, the category key has been extended to include _diffrn_detector.id to uniquely identify each detector. If there is only one detector, _diffrn_detector.id need not be specified, and it will implicitly default to the value of _diffrn_detector.diffrn_id (a pointer to _diffrn.id in the DIFFRN category in the mmCIF dictionary). The general class of detector is given by the value of _diffrn_detector.detector with the make and model given by the value of _diffrn_detector.type. Any special aspects of the detector not covered elsewhere are given by the value of _diffrn_detector.details. As in mmCIF, the value of _diffrn_detector.dtime gives the deadtime of the detector. Additional data items may need to be added in the future for complex inhomogeneous deadtime situations. In addition, the number of axes can be specified using _diffrn_detector.number_of_axes.

Data items in the DIFFRN_DETECTOR_AXIS category associate axes with detectors. Each axis is associated with a detector through the value of _diffrn_detector_axis.detector_id (a pointer to _diffrn_detector.id). The value of *.axis_id (a pointer to _axis.id) identifies an axis. Together *.detector_id and *.axis_id form the category key.

Data items in the DIFFRN_DETECTOR_ELEMENT category record details about the spatial layout and other characteristics of each element of a detector which may have multiple elements, giving the X and Y coordinates of the position of the beam centre relative to the lower left corner of each detector element. Each detector element is identified by the value of _diffrn_detector_element.id and the detector of which it is an element is identified by the value of _diffrn_detector_element.detector_id (a pointer to _diffrn_detector.id).

In most cases, it would be preferable to use the more detailed information provided in the ARRAY_STRUCTURE_LIST and ARRAY_STRUCTURE_LIST_AXIS categories rather than simply specifying the coordinates of the centre of the beam relative to the lower left corner of each detector element.