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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.

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outline
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
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 absorption
Planning an experiment: Absorption

If we accept 60% loss offlux, we can estimate the diameter of capillary to use:

H2O : µ = 0.656

ln(0.4)/-6.626 = 1.4 cm

d ~ 1.8 cm

Al2O3 : µ = 6.626

d ~ 2 mm

GeO2: µ = 96.906

d ~ 0.12 mm

Y2O5: µ = 186.756

d ~ 0.07 mm

TeO2 : µ = 68.607

d ~ 0.18 mm

PbO : µ = 549.499

d ~ 0.03 mm

  • Linear (µ) and mass (µ/ρ) absorption coefficients can be calculated from programs such as XOP(1)

L

2r

Area = πr2

L =(πr2)/2r = π/4 d

~ 3/4 d

planning an experiment absorption1
Planning an experiment: Absorption

Increase Z → increased energy at which K edge occurs.

for region around Ag

(Z > Ag) µ/ρ < (Z <Ag)

HOWEVER, there is also density to consider

slide6

Planning an experiment: Absorption

  • Example: β filter

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.

slide7

Planning an experiment: Beam size

Anti scatter slit

Prog. Rec. slit

Mask

Diameter of sample (L)

Prog. Div. slit

Soller slit

PDS angle (θ)

Soller slit

Detector

Kβ filter

X-ray tube

240 mm (r)

PDS θ (rad) = L/r

ASS= PDS x 2

PRS (mm) = L

slide8

Measurements needed

Once 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 35to 156° to improve statistics at high Q

slide9

GudrunX: What does it do?

  • Calculating the coherent scattering

Measured data

background data

Krogh-Moe – Norman normalisation

Compton scattering

Polarisation

Absorption

slide10

GudrunX: What does it do?

  • Calculating F(Q)

Effect of normalisation:

slide11

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.

slide12

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.
slide13

Beam panel:

  • Requires minimal alteration.
  • Edit the beam size if the beam is smaller that the sample.
  • Ensure the correct bremsstrahlung file is chosen.
slide14

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.

slide15

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)

slide16

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
slide17

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

slide18

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.

slide19

GudrunX: Output files

.subcan

X = 2θ

Y1 = experimental data

Y2 = single atom scattering

Y6 = Bremsstrahlung

slide20

GudrunX: Output files

.soq

X = Q

Y1 = F(Q)

F(Q) will have been normalised to either <f>2 or <f2>. Ensure that you have a record of which you used!

slide21

GudrunX: Output files

.gofr

X = r

Y1 = 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

fluorescence
Fluorescence

X-ray energy > absorption edge in sample → Fluorescence

Fluorescence provides a background which is uniformly distributed across the angular range

fluorescence1
Fluorescence

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.

fluorescence2
Fluorescence

However, if a constant background is subtracting from the Ca/Sr data and THEN the data is scaling:

The characteristic X-ray shape is onceagain present in the data