SILICON: Difference between revisions
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[http://xds.mpimf-heidelberg.mpg.de/html_doc/xds_parameters.html#SILICON= SILICON=] tells XDS what the absorption coefficient of the detector material is. | |||
[http://xds.mpimf-heidelberg.mpg.de/html_doc/xds_parameters.html#SILICON= SILICON=] tells XDS what the absorption coefficient of the detector material is. A more proper name would be SENSOR_ABSORPTION, but historically, silicon was the first sensor material. The absorption of the sensor material needs to be known for two reasons: | |||
# in case of oblique incidence of diffracted x-rays on the detector, the path through the detector's absorbing material is longer than for vertical incidence, so more x-rays are absorbed | # in case of oblique incidence of diffracted x-rays on the detector, the path through the detector's absorbing material is longer than for vertical incidence, so more x-rays are absorbed | ||
# in that situation, the center of gravity of the absorbed x-rays is not at the same position as for an infinitely thin detector, so a positional correction is required | # in that situation, the center of gravity of the absorbed x-rays is not at the same position as for an infinitely thin detector, so a positional correction is required | ||
Both corrections are usually only required at very high resolution, or rather, high two-theta. | Both corrections are usually only required at very high resolution, or rather, high two-theta. | ||
== Usage for CCD detectors == | |||
Actually, if the detector material is silicon, the absorption coefficient is calculated internally within XDS, thus SILICON= is not required. | Actually, if the detector material is silicon, the absorption coefficient is calculated internally within XDS, thus SILICON= is not required. | ||
If however the detector material is GADOX (gadolinium oxysulphide, as used e.g. for ADSC and Mar/Rayonix CCD detectors), then the absorption coefficient can be obtained from the table below, and should be entered manually into the line that has SILICON= in XDS.INP (if required, after uncommenting that line). | If however the detector material is GADOX (gadolinium oxysulphide, as used e.g. for ADSC and Mar/Rayonix CCD detectors; colloquially called ''Phosphor''), then the absorption coefficient can be obtained from the table below, and should be entered manually into the line that has SILICON= in XDS.INP (if required, after uncommenting that line). | ||
SILICON is only useful if SENSOR_THICKNESS is also specified. For the Pilatus detector, the value to be used can usually be obtained from the frame header. For CCD detectors, a typical value of SENSOR_THICKNESS is 0.031, and the SILICON= values in the table are correct for that. | Speifying SILICON is only useful if SENSOR_THICKNESS is also specified. For the Pilatus detector, the value to be used can usually be obtained from the frame header. For CCD detectors, a typical value of SENSOR_THICKNESS is 0.031, and the SILICON= values in the table are correct for that. | ||
Thanks to James Holton and Jason Price for coming up (by actually measuring it) with the SENSOR_THICKNESS value of 0.031, and the table of SILICON= values! The latter assumes that 40% of the 0.031 mm is air, and uses the measured weight of GADOX sheets. Then, specifying a density of 4.2 (which is about 60% of the density of Gd2O2S, 7.32 g/cm^3) on http://henke.lbl.gov/optical_constants/atten2.html one obtains a list of absorption coefficients that can be converted to values close to the SILICON values given in the table below, by using <table_value>=1000/<absorption_coefficient>. | Thanks to James Holton and Jason Price for coming up (by actually measuring it) with the SENSOR_THICKNESS value of 0.031, and the table of SILICON= values! The latter assumes that 40% of the 0.031 mm is air, and uses the measured weight of GADOX sheets. Then, specifying a density of 4.2 (which is about 60% of the density of Gd2O2S, 7.32 g/cm^3) on http://henke.lbl.gov/optical_constants/atten2.html one obtains a list of absorption coefficients that can be converted to values close to the SILICON values given in the table below, by using <table_value>=1000/<absorption_coefficient>. | ||
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<pre> | |||
wave- ene- mu_ | wave- ene- mu_ | ||
length rgy energy | length rgy energy | ||
[A] [eV] absorp SILICON= | [A] [eV] absorp SILICON= | ||
3.0996 4000 244.537 248.401 | 3.0996 4000 244.537 248.401 | ||
3.0919 4010 243.005 246.854 | 3.0919 4010 243.005 246.854 | ||
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0.61992 20000 14.1798 15.466 | 0.61992 20000 14.1798 15.466 | ||
</pre> | </pre> | ||
=== See also === | |||
https://physics.nist.gov/PhysRefData/XrayMassCoef/tab4.html for e.g. CdTe . | |||