data acquisition - penn state college of earth and …ryba/coursework/rietveld... · 2 data...

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Data AcquisitionWhat choices need to be made?

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Data AcquisitionWhat choices need to be made?

Specimen type and preparation

Radiation source

Wavelength

Instrument geometry

Detector type

Instrument setup

Scan parameters

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Data AcquisitionWhat choices need to be made?

Specimen type and preparation

Slide mount

Front loading cavity

Back loading cavity

Side drifting cavity

Low backgrd plate

Several spherical particle techniques

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Data AcquisitionWhat choices need to be made?

Specimen type and preparation

Slide mount

Front loading cavity

Back loading cavity

Side drifting cavity

Low backgrd plate

Several spherical particle techniques

Preferred orientation is worst prep problem

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Data AcquisitionPreferred orientation

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Data AcquisitionPreferred orientation

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Data AcquisitionWhat choices need to be made?

Specimen type and preparation

Slide mount

Front loading cavity

Back loading cavity

Side drifting cavity

Low backgrd plate

Several spherical particle techniques

Low angle problem - fixed divergence slit:

specimen

X

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Data Acquisition

Specimen type and preparation

To get good particle statistics, generally want size < 10 µ

Poorly ground sample:

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Data AcquisitionWhat choices need to be made?

Specimen type and preparation

Slide mount

Front loading cavity

Back loading cavity

Side drifting cavity

Low backgrd plate

Several spherical particle techniques

Neutron diffraction requires larger specimens

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Data AcquisitionWhat choices need to be made?

Radiation sources

Lab x-rays

Rotating anode x-rays

Synchrotron x-rays

Constant wavelength neutrons

TOF neutrons

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Data AcquisitionWhat choices need to be made?

X-rays vs neutrons

X-rays - atomic scatt

power (ƒ) decreases w/

2Θ

Neutrons - atom scatt

cross sections constant

w/ 2Θ

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Data AcquisitionWhat choices need to be made?

X-rays vs neutrons

X-rays - low atomic no.

ƒs very small

Neutrons - little variation

of atom scatt cross

sections w/ atomic no.

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Data AcquisitionWhat choices need to be made?

X-rays vs neutrons

X-rays - low atomic no.

ƒs very small

Neutrons - little variation

of atom scatt cross

sections w/ atomic no.

magnetic spin – use for

magnetic structure detn

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Data AcquisitionWhat choices need to be made?

X-rays vs neutrons

X-rays - usually α1-α2 doublet used (not w/ synchrotron x-rays)

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Data AcquisitionWhat choices need to be made?

X-rays vs neutrons

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Data AcquisitionWhat choices need to be made?

Radiation sources

Lab x-rays

relatively low intensity

Rotating anode x-rays

much higher intensity

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Data AcquisitionWhat choices need to be made?

Radiation sources

Lab x-rays

relatively low intensity

Rotating anode x-rays

much higher intensity

Synchrotron x-rays

extremely high intensity

monochromatic

continuously variable wavelength

very tiny beam

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Data AcquisitionWhat choices need to be made?

Radiation sources

Lab x-rays

relatively low intensity

Rotating anode x-rays

much higher intensity

Synchrotron x-rays

extremely high intensity

monochromatic

continuously variable wavelength

very tiny beam

very highresolution

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Data AcquisitionWhat choices need to be made?

Radiation sources

Reactor neutrons

continuous wave-

length distribution –

monochromator

req'd

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Data AcquisitionWhat choices need to be made?

Radiation sources

Reactor neutrons

continuous wave-

length distribution –

monochromator

req'd

generally low flux,

low resolution

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Data AcquisitionWhat choices need to be made?

Radiation sources

Spallation source

(pulsed)

time-of-flight (TOF)

energy (wavelength)

analysis used

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Data AcquisitionWhat choices need to be made?

Radiation sources

Spallation source

(pulsed)

time-of-flight (TOF)

energy (wavelength)

analysis used

very high flux,

high resolution

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Data AcquisitionWhat choices need to be made?

Radiation sources

Spallation source

(pulsed)

time-of-flight (TOF)

energy (wavelength)

analysis used

very high flux,

high resolution

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Data AcquisitionWhat choices need to be made?

Wavelength

Shorter wavelengths –  more Bragg peaks

more peak overlap

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Data AcquisitionWhat choices need to be made?

Wavelength

Shorter wavelengths –  more Bragg peaks

more peak overlap

(keep in mind peak broadening due to sample

and/or no. phases present)

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Data AcquisitionWhat choices need to be made?

Wavelength

Shorter wavelengths –  more Bragg peaks

more peak overlap

(keep in mind peak broadening due to sample

and/or no. phases present)

X-rays – most atom types have very strong absorption

of characteristic wavelengths

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Data Acquisition

Instrument geometry

Choices:

a. conventional Bragg-Brentano diffractometer (includes Θ-Θ)

b. Guinier camera or diffractometer

c. diffractometer w/ curved PSD

d. TOF neutron instrument

e. 4-circle diffractometer

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Data Acquisition

Instrument geometry

Choices:

a. conventional Bragg-Brentano diffractometer (includes Θ-Θ)

b. Guinier camera or diffractometer

c. diffractometer w/ curved PSD

d. TOF neutron instrument

e. 4-circle diffractometer

Generally want good resolution & high intensity – can be

obtained w/ all but (c) above, & (a) w/reactor neutrons (CW)

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Data Acquisition

Instrument geometry

Choices:

a. conventional Bragg-Brentano diffractometer (includes Θ-Θ)

b. Guinier camera or diffractometer

c. diffractometer w/ curved PSD

d. TOF neutron instrument

e. 4-circle diffractometer

Generally want good resolution & high intensity – can be

obtained w/ all but (c) above, & (a) w/reactor neutrons (CW)

Instrument geometry affects instrument file

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Data AcquisitionWhat choices need to be made?

Detector type

Conventional – scintillation or proportional counterenergy resolution not high – usuallyneed monochromator

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Data AcquisitionWhat choices need to be made?

Detector type

Conventional – scintillation or proportional counterenergy resolution not high – usuallyneed monochromator

Also common – solid state detector – very high energy resolution – monochromator not needed

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Data AcquisitionWhat choices need to be made?

Detector type

Conventional – scintillation or proportional counterenergy resolution not high – usuallyneed monochromator

Also common – solid state detector – very high energy resolution – monochromator not needed

Neutrons – He counter

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Data AcquisitionWhat choices need to be made?

Detector type

Conventional – scintillation or proportional counterenergy resolution not high – usuallyneed monochromator

Also common – solid state detector – very high energy resolution – monochromator not needed

Neutrons – He counter

What about image plates? – poor resolution, hi bkgrd

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Data AcquisitionWhat choices need to be made?

Instrument setup

Divergence and receiving slit sizes

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Data AcquisitionWhat choices need to be made?

Instrument setup

Divergence and receiving slit sizes

Theta-compensating divergence slit keeps irradiated area constant,But changes intensity distribution vs 2Θ

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Data AcquisitionWhat choices need to be made?

Instrument setup

Divergence and receiving slit sizes

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Data AcquisitionWhat choices need to be made?

Instrument setup

Divergence and receiving slit sizes

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Data AcquisitionWhat choices need to be made?

Instrument setup

Divergence and receiving slit sizes

Use of monochromator changes polarization correctionin LP factor

Integrated intensities of Bragg reflections:

Ihkl = scale factor x mult factorhkl x LPΘ x absorb factorΘ xpref orient factorhkl x extinction factorhkl x | Fhkl | 2

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Data AcquisitionWhat choices need to be made?

Scan setup

Scan range

no. of reflections – want >5 x no. parameters refined wavelength dependent low angle reflections may not be useful due to

specimen configurationlarger inherent instrumental errorsextinction effects

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Data AcquisitionWhat choices need to be made?

Scan setup

Step size

sample dependent - peak widths need 5 observations across top of peak usually 0.01 - 0.05° 2Θ

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Data AcquisitionWhat choices need to be made?

Scan setup

Step size

sample dependent - peak widths need 5 observations across top of peak usually 0.01 - 0.05° 2Θ

Count time

longer times ––> higher intensities ––> greater precision at some point, little improvement in refinement process for longer count times

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Data AcquisitionWhat choices need to be made?

Specimen type and preparation

Radiation source

Wavelength

Instrument geometry

Detector type

Instrument setup

Scan parameters

Choose according to objective(s) of experiment