XND 1.2 : Experiment description in the input file.

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Introduction

The block has to be repeated for each different experience according to the nExp=@XND(EXPER) value declared in the program header; any experience can obviously contain more diagrams and any diagrams more phases. The experiment block contain the following header and variables blocks.

the experiment header
the wavelength block
the background block
the alignment block
the profile block
the asymmetry block

Experiment Header

The header from the previous 1.1 release are still recognised. In the 1.2 release the header uses keys. If the @EXPER key is not found after the title a 1.1 header is assumed.

@EXPER key identifier
NATURE d 0 0 X-ray
1 neutron, single wavelenght
2 anomalous X-ray scattering
3 (neutron, reserved for magnetic structures)
16
32
TECHN d 0 0 X-ray Bragg-Brentano geometry (symmetric reflection, centering depend on cos_t) neutron, single wavelenght (transmission)
1 (reserved for X-ray, asymmetric reflection)
2 (reserved for X-ray, linear detector)
3 (reserved for X-ray, courbed detector, centering depend on sin_2t)
+4 apply absorption correction for transmission experiment
+8 apply absorption correction for fixed grazing incidence reflection experiment
DATA d 1 number of diagrams collected in the experience
FILE d 1 file type identifier (see Data File Formats)
LAMBDA d 1 number of wavelenghts
BGROUND d 2 >0 number of points for background definition, common to all diagrams
<0 - number of points for background foreach diagram
ORIG f 0.0 origin of polynomial development
TITLE s label of the experience

@EXPER				key identifier
NATURE	d	0	0	X-ray
1	neutron, single wavelenght
2	anomalous X-ray scattering
3	(neutron, reserved for magnetic structures)
16
32
TECHN	d	0	0	X-ray Bragg-Brentano geometry (symmetric reflection, centering depend on cos_t) neutron, single wavelenght (transmission)
1	(reserved for X-ray, asymmetric reflection)
2	(reserved for X-ray, linear detector)
3	(reserved for X-ray, courbed detector, centering depend on sin_2t)
+4	apply absorption correction for transmission experiment
+8	apply absorption correction for fixed grazing incidence reflection experiment
DATA	d	1		number of diagrams collected in the experience
FILE	d	1		file type identifier (see Data File Formats)
LAMBDA	d	1		number of wavelenghts
BGROUND	d	2	>0	number of points for background definition, common to all diagrams
<0	- number of points for background foreach diagram
ORIG	f	0.0		origin of polynomial development
TITLE	s			label of the experience

Data identification

The following key @DATA is repeated nDiag=@EXPER(DATA) times. Its content depends on the FileType. If @DATA is not found, xnd search for 1.1 style lines.

@DATA key identifier
if (FileType=@EXPER(FILE)=0) (simulation mode, no data to read)
START d 5 First point in the simulated data set
STOP d 120 Last point in the simulated data set
STEP d 1.0 step between points
TEMP f 0.0 value of Temp for the current simulated diagram
if (FileType=@EXPER(FILE)=20 or 21) (multiples banks)
SIZE d number of points on the data file
SUM d 1 number of successive diagrams to be cumulated
SKIP d 0 number of following diagrams to be skipped
VAR d 1 control parameter, Temp is the Numvar parameter in the header
MONIT f 0 or value of the renormalization monitor
FILE s name of the data file
TEMP f 0.0 starting value of Temp
otherwise
FILE s name of the data file
SIZE d number of points in the data file, these value is only checked when a binary data file is used
TEMP f 0.0 value of Temp for the current diagram

@DATA			key identifier
if (`FileType=@EXPER(FILE)`=0) (simulation mode, no data to read)
START	d	5	First point in the simulated data set
STOP	d	120	Last point in the simulated data set
STEP	d	1.0	step between points
TEMP	f	0.0	value of `Temp` for the current simulated diagram
if (`FileType=@EXPER(FILE)`=20 or 21) (multiples banks)
SIZE	d		number of points on the data file
SUM	d	1	number of successive diagrams to be cumulated
SKIP	d	0	number of following diagrams to be skipped
VAR	d	1	control parameter, `Temp` is the Numvar parameter in the header
MONIT	f	0	or value of the renormalization monitor
FILE	s		name of the data file
TEMP	f	0.0	starting value of `Temp`
otherwise
FILE	s		name of the data file
SIZE	d		number of points in the data file, these value is only checked when a binary data file is used
TEMP	f	0.0	value of `Temp` for the current diagram

Wavelength block

@LAMDA	key identifier of the variable block
the following group of lines is repeated `Nlambda=@EXPER(LAMBDA)` times
`lambda`	$	the value of the wavelength
`Int`	$	Intensity of the wavelength
`W_l(tan theta)`	$	spectral lorentzian width, coefficient of the lorentzian composant varying as `tan(theta)-tan(theta_min)`
`W_g(tan theta)`	$	spectral gaussian width, this is the coefficient of the gaussian composant varying as `tan(theta)-tan(theta_min)`

Background block

@BGROUND	key identifier of the variable block
the following group of lines is repeated `nBckg=@EXPER(BGROUND)` times
`2theta_i`	f	angle of the selected background point
`Int_bkg_i`	$	Intensity of the background at `2theta_i`

Alignment block

Some parameters are not fully implemented, in this block the derivatives calculation is done only for the 4 first variables in xnd_1.25; trying to refine them may lead to system errors. This has to be corrected in a few.

@SETTING	key identifier of the variable block
`Zero`	$	error on the absolute position of `2theta` counter in degrees
`Polar`	$	correction of polarisation : cos^2(2theta_mono)
		0	neutron or synchrotron radiation data
		1	filtered X-ray data
		0.8357	Cu-K_beta radiation, graphite monochromator
`t_mono`	$	tangent of the minimum of the spectral distribution (`-v/2u` of classical Rietveld)
`s_Eclair`	$	intensity correction (rectangular sample) at low angle for illumination if `sin(theta) < s_Eclair` the intensities are corrected according to `sin(theta)/s_eclair`
if `Techn=@EXPER(TECHN) == 4, 8`
`Zero_theta`	$	not used
if `Techn=@EXPER(TECHN) == 1, 5, 9`
`Zero_theta`	$	difference `theta - 2theta/2` or fixed angle incidence
if `Techn=@EXPER(TECHN) == 2, 3, 6, 7, 10, 11`
`alpha`	$	fixed incidence angle
if `Techn=@EXPER(TECHN) == 4, 5, 6, 7 (transmission with absorption correction)`
`Abs_cyl`	$	absorption (mu.R) for cylinders
`Abs_pl`	$	absorption (mu.L) for plates
if `Techn=@EXPER(TECHN) == 8, 9, 10, 11 (reflection with absorption correction)`
`Alpha_c`	$	critical angle
`Mu`	$	absorption length

Instumental profile block

@INSTRU	key identifier of the variable block
`Wl0`	$	constant lorentzian linewidth
`Wg0`	$	constant gaussian linewidth
`Wl_T2`	$	lorentzian linewidth varying with `1/tan(2theta)` like axial divergency
`Wg_T2`	$	gaussian linewidth varying with `1/tan(2theta)` like axial divergency
if `Techn=@EXPER(TECHN) == 3,7,11 (cylinder detectors)` dependance of sin(TTH-alpha)
`WlSa`	$	linear lorentzian linewidth
`WgSa`	$	linear gaussian linewidth
`WlS2a`	$	quadratic lorentzian linewidth
`WgS2a`	$	quadratic gaussian linewidth

Asymmetry block

Various cases have to be considered according to the value of mAsym=@MODES(ASYM) in the header.
If asym =< 0 we will first read the convolution parameters, Note that if a Pseudo-Voigt is used, the convolution process is analytic but for the real Voigt no analytic formulation allow to solve the convolution process.

@ASCNV	key identifier of the variable block
`h+s_r`	$	sum (h+s) of detector and sample axial appertures divided by their distance
`d_h+s`	$	relative value of the difference \|h-s\|/h+s of detector and sample axial appertures

If (asym != 0) we read the coefficents of the asymmetry expansion

@ASYM	key identifier of the variable block
the following group of lines is repeated according to `mAssym` in the program header
`A_T2`	$	asymmetry coefficient varying with `1/tan(2theta)`
`A_T`	$	asymmetry coefficient varying with `1/tan(theta)`
`AS2`	$	asymmetry coefficient varying with `sin(2 theta)`

Complementary experimental block

@C_EXP	key identifier of the variable block
`resol`	$	analysor resolution dlambda/lambda (read only if nature == 16

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