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Data Collection Sequence for the X-ray Image
Intensifier/CCD Detector System
This is an overview of a full calibration/ data collection
strategy necessary to obtain quantitative results from the X-ray Image
Intensifier/CCD read-out detector system (XRII/CCD) [21,22]
or similar detector system. It is intended as a check list for
anyone performing a
crystallography experiment. Aspects which require further consideration
are discussed in Section 16.5.
The following list is for measurements which may be performed separately from
the data collection, before or after.
- 1a: Calibration measurements to determine intensity non-linearity.
At present the ESRF XRII/CCD system appears to be sufficiently
linear to avoid the need for correction.
- 1b: Collect response of CCD camera to uniform light source
(illuminated piece of paper). ``Correct for dark count'' to get CCD
uniformity of response function. (Averaging images will improve
accuracy.) (Probably performed before the experiment, at the normal
operating temperature.)
- 1c: Place diffuse scatterer/fluorescent cell at the sample position.
- 1d: Take 1-D 2 scan of diffuse source/fluorescent cell
distribution. At each
angular position the counter must be left long enough to reduce counting
statistics to the required level. (Scans at other angles than the plane
of the synchrotron may be useful if it is possible to obtain these.)
- 1e: Recording the 2-D source distribution on X-ray film or image
plates may be useful to verify the extent to which the intensity
distribution is circular symmetric.
- 1f: Collect reference 2 scan without diffuse
scatterer/fluorescent cell, or with cell containing only solvent.
This is a proposed sequence for efficient collection
crystallography and calibration data. This pre-supposes that the
detector linearity is known, that the CCD pixel to pixel flat-field
response is available, and that a diffuse scatterer with a known angular
distribution of intensity for the required wavelength is available. (The
order is the result of practical experience.)
- 2a: Place calibration grid on the detector.
- 2b: Place diffuse scatterer/fluorescent cell at sample position.
- 2c: Measure sample to mask distance.
- 2d: Collect spatial distortion calibration grid image.
- 2e: Collect flood-field image with diffuse scatterer/fluorescent cell.
- 2f: Remove diffuse scatterer/fluorescent cell.
- 2g: Collect reference image for flood-field exposure integration
time without fluorescent cell, or with cell containing only solvent.
- 2h: Collect beam centre image or ``wax'' image, unless a
semi-transparent beam-stop is being used.
- 2i: Place sample at sample position.
- 2j: Collect diffraction data images (without changing the magnetic
environment e.g. Do not change the position of large metallic objects
such as the diffractometer cradle).
- 2k: Collect ``dark count'' (empty capillary) images for standard data
exposure integration time(s). (Averaging images will improve accuracy.)
- 2l: If data must be collected in a different magnetic configuration
the spatial distortion and ideally the flood-field response should
be re-calibrated. (Repeat steps 2a-2h.)
- 2m: Remove sample
- 2n: Place diffuse scatterer/fluorescent cell at sample position.
- 2o: Collect flood-field image.
- 2p: Collect spatial distortion calibration grid image.
- 2q: Collect reference image for flood-field exposure integration
time without fluorescent cell, or with cell containing only solvent.
(Steps 2n-2q are included to verify if that the spatial
distortion has remained constant since it was last calibrated.)
Next: Notes on the Data
Up: Calibration Sub-menu
Previous: Non-Uniformity of Sensitivity Response
Andrew Hammersley
2004-01-09