Calibration Procedures - Revision history

Brian: /* Summary of Calibration Procedures */

2013-08-30T01:55:35Z

Summary of Calibration Procedures

← Older revision		Revision as of 01:55, 30 August 2013
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	This project to gather information is new and we hope to have some information soon.		This project to gather information is new and we hope to have some information soon.

	A comprehensive review discussing all possible data correction steps (in particular for X-ray scattering instrumentation) is available here: http://~~arxiv~~.org/~~abs~~/~~1306.0637~~		A comprehensive review discussing all possible data correction steps (in particular for X-ray scattering instrumentation) is available here: http://dx.doi.org/10.1088/0953-8984/25/38/383201

	==Quokka - Bragg Institute, ANSTO==		==Quokka - Bragg Institute, ANSTO==

Katy wood at 06:35, 17 June 2013

2013-06-17T06:35:25Z

← Older revision		Revision as of 06:35, 17 June 2013
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	===Absolute Intensity===		===Absolute Intensity===
			Data is put on an absolute scale using the direct beam measurement with a calibrated attenuator, using the NIST macros for Igor Pro with Quokka specific modifications, (S.R. Kline, ''J Appl Crystallogr'', 2006, 39, 895-900). As per the help file accessible in the NIST macros, the absolute intensity is calculated as:
			I_abs=I_cor/(κ d T_sam )
			Where I_cor is the measured data corrected for the instrument background, detector sensitivity and nornalised to monitor counts, d is the sample thickness and T_sam is the sample transmission.κ is a scaling factor, calculated from the attenuated direct beam measurement taken in the same configuration as the sample measurement:
			κ=Totcnts_DB/(Moncnts_DB×Attfactor_DB )×∆Ω
			Where Totcnts_DB is the number of counts in the direct beam, Moncnts_DB the monitor counts for the direct beam measurement, Attfactor_DB the attenuation factor for the attenuator used and ∆Ω is the solid angle subtended by one pixel.


			Calculation of attenuation factors on Quokka
			(thanks to discussions with John Barker, NIST):

			On Quokka, a wheel of 25 mm thick plexiglas is used to attenuate the beam, where different thicknesses of plexiglas have been milled out around the wheel, leaving 12 attenuators of different thickness, from 25mm down to 0. Attenuation factors for the 12 attenuators were measured with the detector to sample position of 20m, a 50mm diameter source aperture and 20m source to sample distance. Attenuation factors are calculated by taking the ratio of counts in the direct beam with and without the attenuator in the beam. To avoid over-exposing the detector, this is done with various sized apertures at the sample position, and the values are normalised by the ratio of the same attenuation value measured with different aperture sizes. On Quokka four different aperture sizes were found to be necessary to cover all attenuation values.
			The factors have been calculated for different wavelengths (5, 6, 7, 8Å) and interpolations are performed if data is measured at an intermediate wavelength.

			The error on the attenuator factors for the plexiglas attenuators is less than 2%. Generally transmission measurements and direct beam measurements are performed so that the error is less than 1% (120 seconds counting time with appropriate attenuator in the beam). The errors are given taking into account counting statistics on the instrument detector only.

			--[[User:Katy wood\|Katy wood]] 01:35, 17 June 2013 (CDT)
	===Detector Response/Flat Field===		===Detector Response/Flat Field===

Brian: /* Summary of Calibration Procedures */

2013-06-06T02:57:35Z

Summary of Calibration Procedures

← Older revision		Revision as of 02:57, 6 June 2013
Line 4:		Line 4:
	This project to gather information is new and we hope to have some information soon.		This project to gather information is new and we hope to have some information soon.

			A comprehensive review discussing all possible data correction steps (in particular for X-ray scattering instrumentation) is available here: http://arxiv.org/abs/1306.0637

	==Quokka - Bragg Institute, ANSTO==		==Quokka - Bragg Institute, ANSTO==

AdrianRennie: /* Wavelength : Time-of-Flight (TOF), i.e. Optically-blind double-chopper (Astrium) : Estimated Precission ~?% */

2013-05-14T15:15:22Z

Wavelength : Time-of-Flight (TOF), i.e. Optically-blind double-chopper (Astrium) : Estimated Precission ~?%

← Older revision		Revision as of 15:15, 14 May 2013
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	Selector resolution, dlambda/lambda, may also be determined from the TOF profiles from the triangular fit or numerical standard deviation		Selector resolution, dlambda/lambda, may also be determined from the TOF profiles from the triangular fit or numerical standard deviation

	==== Wavelength : Time-of-Flight (TOF), i.e. Optically-blind double-chopper (Astrium) : Estimated ~~Precission~~ ~?%====		==== Wavelength : Time-of-Flight (TOF), i.e. Optically-blind double-chopper (Astrium) : Estimated Precision ~?%====

	D33 possess 4 choppers with spacings between choppers 1 & 2 of 2.8m, choppers 2 & 3 of 1.4m and choppers 3 & 4 of 0.7m. All choppers have a window opening of 110 degrees with electronic trigger pickup located on the opening edge of the window when turning anti-clockwise looking downstream. In principle only two choppers are required at any one time operating in the 'optically blind' mode, i.e. the upstream chopper of the pair closes a the same moment the downstream chopper opens. The spacing between the chopper pair, dD, relative to the total flight distance, mid-chopper-pair to detector, D, determines the wavelength resolution, dl/l. It is the calibration of the chopper delay angle, i.e. when the trigger signal arrives relative to the window cutting the mid-point of the neutron guide, OR the relative phasing of chopper pair also determined by the pickup 'zero' angle that is required to accurately calibrate neutron wavelengths in TOF mode to ensure a well calibrated 'optically blind', 'over-' or 'under-closed' chopper operation.		D33 possess 4 choppers with spacings between choppers 1 & 2 of 2.8m, choppers 2 & 3 of 1.4m and choppers 3 & 4 of 0.7m. All choppers have a window opening of 110 degrees with electronic trigger pickup located on the opening edge of the window when turning anti-clockwise looking downstream. In principle only two choppers are required at any one time operating in the 'optically blind' mode, i.e. the upstream chopper of the pair closes a the same moment the downstream chopper opens. The spacing between the chopper pair, dD, relative to the total flight distance, mid-chopper-pair to detector, D, determines the wavelength resolution, dl/l. It is the calibration of the chopper delay angle, i.e. when the trigger signal arrives relative to the window cutting the mid-point of the neutron guide, OR the relative phasing of chopper pair also determined by the pickup 'zero' angle that is required to accurately calibrate neutron wavelengths in TOF mode to ensure a well calibrated 'optically blind', 'over-' or 'under-closed' chopper operation.
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	Method 2: (Cubitt D17 & Figaro method)		Method 2: (Cubitt D17 & Figaro method)



	===Absolute Intensity===		===Absolute Intensity===

AdrianRennie: Spelling

2013-05-14T15:14:56Z

Spelling

← Older revision		Revision as of 15:14, 14 May 2013
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	==== Wavelength : Monochromatic, i.e. Velocity Selector (Astrium) : Estimated ~~Precission~~ ~0.5%====		==== Wavelength : Monochromatic, i.e. Velocity Selector (Astrium) : Estimated Precision ~0.5%====

	Install a small beam chopper at the sample position. Accuracy in positioning or delay angle of the trigger pickup are not important. Spin the chopper at a frequency sufficiently slow as to allow neutrons of a given wavelength to reach the furthest detector position.		Install a small beam chopper at the sample position. Accuracy in positioning or delay angle of the trigger pickup are not important. Spin the chopper at a frequency sufficiently slow as to allow neutrons of a given wavelength to reach the furthest detector position.
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	Selector resolution, dlambda/lambda, may also be determined from the TOF profiles from the triangular fit or numerical standard deviation		Selector resolution, dlambda/lambda, may also be determined from the TOF profiles from the triangular fit or numerical standard deviation


	==== Wavelength : Time-of-Flight (TOF), i.e. Optically-blind double-chopper (Astrium) : Estimated Precission ~?%====		==== Wavelength : Time-of-Flight (TOF), i.e. Optically-blind double-chopper (Astrium) : Estimated Precission ~?%====

Dewhurst: /* D33 - Institut Laue Langevin, Grenoble, France */

2013-05-14T13:20:50Z