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[Imgcif-l] Cylindrical detectors

• To: imgcif-l@iucr.org
• Subject: [Imgcif-l] Cylindrical detectors
• From: "James Hester" <jamesrhester@gmail.com>
• Date: Wed, 1 Aug 2007 17:08:39 +1000

I have a question relating to describing cylindrical detectors (e.g.
Debye-Scherrer camera using image plates) in imgCIF.  There appear to be no
examples in the 'canonical' imgCIF literature relating to such non-flat
detectors, let me give my best shot here - I would appreciate any feedback
as to the correctness of this description, particularly the characterisation
of the array structure axis as a detector rotation axis located at the
sample.

Is it reasonable to use _array_structure_list_axis.angle_increment instead
of displacement_increment?

Note that the radius of curvature of the detector is implied by the offset
of the other detector axis, and once this is given the pixel displacement
increment can be converted to degrees.

For a cylindrically curved detector located 573mm from the sample, I would
guess the following axis definitions:

##########
loop_
_axis.id
_axis.type
_axis.equipment
_axis.depends_on
_axis.offset[1] _axis.offset[2] _axis.offset[3] _axis.vector[1]
_axis.vector[2] _axis.vector[3]

source       .        source       .        0 0 0   0 0 1
omega  rotation   goniometer .        0 0 0   1 0 0
det_up       .        detector     .        0 0 -573  1 0 0   #parallel to
sample rotation axis but on surface of
det_along  rotation  detector  .        0  0 0   1 0 0     #coincident with
sample rotation

# the image that comes off is 2000x4000 pixels, with the fast and short
direction in the cylindrical z #direction:

loop_
_array_structure_list.axis_set_id
_array_structure_list.dimension
_array_structure_list.precedence

det_up   2000  1
det_along 4000 2

#vertical and horizontal pixels are 100 microns in size...

loop_
_array_structure_list_axis.axis_id
_array_structure_list_axis.displacement_increment

det_up    0.1
det_along  0.1
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