analysing x-ray data using gudrunx
DESCRIPTION
Analysing X-ray data using GudrunX. Outline. Planning an experiment Absorption Fluorescence Beam size Data required Outline of analysis process Step by step guide through analysis Practice with some data! SiO 2 H 2 O Tellurite glass. Planning an experiment. - PowerPoint PPT PresentationTRANSCRIPT
Analysing X-ray data using GudrunX
0 2 4 6 8 10 12 14 16 18-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
X-r
ay i(Q)
Q (Å-1)
Ca60
Mg25
Cu15
Ca60
Mg20
Cu20
Ca60
Mg15
Cu25
Outline• Planning an experiment
– Absorption– Fluorescence– Beam size
• Data required• Outline of analysis process• Step by step guide through analysis• Practice with some data!
– SiO2
– H2O– Tellurite glass
Planning an experiment• Before starting an experiment it is important to have a very good idea of
your sample composition and density.
• This information will help identify any potential problems which may arise, such as:– Absorption +capillary size– Beam size– Measurements required– Fluorescence (We’ll return to this later)
• A good idea of potential problems will help you plan the length of your experiment too.– Strongly absorbing/weakly scattering or strongly fluorescent samples
may require longer data collection
• Consider what your data will be used for and what quality you require.
Planning an experiment: AbsorptionIf we accept 60% loss of
flux, we can estimate the diameter of capillary to use:
H2O : µ = 0.656ln(0.4)/-6.626 = 1.4 cm
d ~ 1.8 cm
Al2O3 : µ = 6.626d ~ 2 mm
GeO2 : µ = 96.906d ~ 0.12 mm
Y2O5 : µ = 186.756d ~ 0.07 mm
TeO2 : µ = 68.607d ~ 0.18 mm
PbO : µ = 549.499d ~ 0.03 mm
Linear (µ) and mass (µ/ρ) absorption coefficients can be calculated from programs
such as XOP(1)
Area = πr2 L =(πr2)/2r = π/4 d ~ 3/4 d
2r
L
0 10 20 30 40 50 60 70 80 900
20
40
60
80
100
Mas
s A
bsor
ptio
n co
effic
ient
(Ag
K)
Element
Ag10000 1000000.1
1
10
100
1000 Ge (32) Y (39) Te (52)
Mas
s A
ttenu
atio
n co
effic
ient
Energy (eV)
AgIncrease Z → increased energy at
which K edge occurs.
for region around Ag (Z > Ag) µ/ρ < (Z <Ag)
Planning an experiment: Absorption
HOWEVER, there is also density to consider
A Material chosen as a β filter must have an absorption edge which lies between the Kα
and Kβ peaks.For an Ag tube, Rh is used.
20000 25000 300000
200
400
600
800
linea
r abs
orpt
ion
coef
ficie
nt c
m-1
Energy (eV)
K K
Planning an experiment: Absorption
Example: β filter
Planning an experiment: Beam size
Prog. Rec. slit
Anti scatter slit
X-ray tubeKβ filter
Soller slit
Prog. Div. slit
Mask
Soller slit
Detector
Capillary size
PDS ASS
0.5 1/8 1/4
1 1/4 1/2
1.5 1/2 1
2 1/2 1
2.5 1 2
3 1 2Table 1: PDS and ASS
settings
240 mm (r)
PDS angle (θ) Diameter of sample (L)
PDS θ (rad) = L/r
ASS= PDS x 2 PRS (mm) = L
Measurements neededOnce the experimental setup has been decided up, three measurements are required – as with Neutron analysis,
these are:
Background
Sample in capillary
Empty capillary
All these measurements need to be taken under the SAME CONDITIONS.
The current set up is to collect data at 0.2° intervals from 3.2 – 156°.
At each point, data is collected of 30 seconds.
There is the option to collect two sets of data:
Several repeat scans from 3.2 to 156°Additional scans from 35 to 156° to
improve statistics at high Q
GudrunX: What does it do?
Krogh-Moe – Norman normalisation
Polarisation
Absorption
Compton scattering
• Calculating the coherent scattering
Measured data background data
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1x105
2x105
3x105
4x105
5x105
6x105 raw data corrected for
absorption & polarisation
Inte
nsity
Q (Å-1)
5 10 15 20-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
S(Q
)
Q
S(Q)
GudrunX: What does it do?
20 40 60 80 100 120 1400
20
40
60
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100
120
Inte
nsity
2
Experimental data Self scattering
4 8 12 16 20
-100
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-60
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-20
0
20
40
S(Q
)
Q
S(Q)
sample <f>2 <f2> %diff
SiO2 100 108 8%
Ga2O3 309.7 448 44%
Effect of normalisation:
• Calculating F(Q)
Installing GudrunX
The X-ray diffractometer webpages can be found at http://www.isis.stfc.ac.uk/support-laboratories/xrd/xrd9446.html
OR as a link from the disordered materials group web page.
Instrument panel:The required files are all located in the gudrunX folder.
• User may wish to alter the Q range of the F(Q) produced, depending on the quality of the data.
• The Qmax should be set to the final Qmax you chose for you data.
Beam panel:Requires minimal alteration.
• Edit the beam size if the beam is smaller that the sample.
• Ensure the correct bremsstrahlung file is chosen.
Normalisation panel:
User must choose which method of normalisation they wish to apply to the data.
Altering Breit-Dirac factor and Overlap factor can give some improvements to the extracted F(Q). Maintain default values initially.
Sample background panel:Select an appropriate sample background panel.
‘Read data’ will display the information from the .XRDML file, including number of scans and the range of angles over which the chosen data set has been
measured.
Set sample background factor (between 0.9 and 1)
Sample specific information required:
Once the instrument and background information has been checked, new tabs need to be added to give sample specific information.
As with GUDRUN this includes a sample and a sample container tab.
Information required includes:
Sample specific information:•Composition•Effective density•Sample size•Fluorescence - a problem for elements in the same row as Ag (Rb – Te)•Multiple scattering
Experimental setup:•Polarisation - 0•Compton scattering - 1•Bremsstrahlung - 0.4
Container panel:Composition, container size (inner and outer dimensions), effective density.
For density either the measured effective density can be given, with a tweak factor = 0
Or the bulk density can be used with the tweak factor alteredEffective density = bulk density/tweak factor
Sample panel:Basic information + fluorescence, multiple scattering etc.
Ensure that packing fraction is sensible (measure or estimate it ~60%)Vary effective density and multiple scattering first, then bremsstrahlung.
Only apply fluorescence for samples containing Rb – Te.
GudrunX: Output files
.subcanX = 2θY1 = experimental dataY2 = single atom scatteringY6 = Bremsstrahlung
GudrunX: Output files
.soqX = QY1 = F(Q)
F(Q) will have been normalised to either <f>2 or <f2>. Ensure that you have a record of which you used!
.gofrX = rY1 = G(r)
Quality of G(r) can be improved by varying parameters in GudrunX. Alternatively, the fourier transform software in Open Genie can be used.
Daniel will be discussing the relationship between various correlation functions
GudrunX: Output files
Fluorescence
1000 10000 1000001
10
100
1000
10000 Ca Sr Ag K edge
Mas
s ab
sorp
tion
coef
ficie
nt
Energy (eV)
0 20 40 60 80 100 120
0
500
1000
1500
2000
2500
3000
3500
4000 Ca bioglass Ca/Sr bioglass Empty SiO
2 capillary
Inte
nsity
(cps
)
Angle
X-ray energy > absorption edge in sample → Fluorescence
Fluorescence provides a background which is uniformly distributed across
the angular range
Fluorescence
1000 10000 1000001
10
100
1000
10000 Ca Sr Ag K edge
Mas
s ab
sorp
tion
coef
ficie
nt
Energy (eV)
0 20 40 60 80 100 120
0
500
1000
1500
2000
2500
3000
3500
4000 Ca bioglass Ca/Sr bioglass Empty SiO
2 capillary
Inte
nsity
(cps
)
Angle
0 20 40 60 80 100 120
0
500
1000
1500
2000
2500
3000 Ca bioglass Ca/Sr bioglass Empty SiO2 capillary
Inte
nsity
(cps
)
Angle
Multiplying the data measured for the empty capillary and Ca/Sr glass data by a scale factor to match the Ca glass data (at high angle) gives:
The shape of the capillary and calcium data are well matched.
Problem with strontium sample.
Fluorescence
1000 10000 1000001
10
100
1000
10000 Ca Sr Ag K edge
Mas
s ab
sorp
tion
coef
ficie
nt
Energy (eV)
0 20 40 60 80 100 120
0
500
1000
1500
2000
2500
3000
3500
4000 Ca bioglass Ca/Sr bioglass Empty SiO
2 capillary
Inte
nsity
(cps
)
Angle
However, if a constant background is subtracting from the Ca/Sr data and THEN the data is scaling:
0 20 40 60 80 100 120
0
500
1000
1500
2000
2500
3000 Ca bioglass Ca/Sr bioglass Empty SiO
2 capillary
Inte
nsity
(cps
)
Angle
The characteristic X-ray shape is onceagain present in the data