Transcript High-Speed PIXE - Surrey Ion Beam Centre

High-Speed PIXE
A spatially resolved PIXE setup at the
6 MV Tandem accelerator
Josef Buchriegler
J.v. Borany, D. Hanf, F. Munnik, S. Nowak, A. Renno, O. Scharf, R. Ziegenrücker
SLcam® User Workshop – 16. Jan. 2014
Text optional: Institutsname  Prof. Dr. Hans Mustermann  www.fzd.de  Mitglied der Leibniz-Gemeinschaft
Outline
1. PIXE fundamentals & Motivation
2. Experimental setup
3. Data evaluation & First results
4. Prospects & Challenges
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PIXE
Fundamentals of PIXE: Particle Induced X-ray Emission
Photon
Particle
Electrons
+
e.g. Mg
Particles: charged ions (mostly protons or He-ions with 2 – 4 MeV)
Ionisation cross-section σ: probability for an inner-shell ionisation
Fluorescence yield ω: probability for a X-ray (or Auger-electron) emission
Photons: typical energies from 1 – 30 keV (K- and L-lines)
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PIXE
Fundamentals of PIXE: X-Ray detection & data evaluation
Detector:
cooled semi-conductor crystal
 Si(Li) or Ge (energy
dependent efficiency)
Spectrum:
detected X-ray photons as a
function of energy
Elements in spectrum:
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
X-ray lines: needs model for X-ray lines (shape) and intensity ratios
Background: subtraction by using a filtering method or background-model
Pileup: caused by (almost) simultaneous detection of two photons
Si escapes: interaction of photons with the detector crystal
 considering all these points  fit X-ray intensities to deduce elemental composition
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PIXE
Fundamentals of PIXE: classical micro-beam setup
High-energy
proton beam
(3 µA)
Aperture
1x1 mm2
Target plane
Object
50x50 μm2
Lens
proton beam on
sample: 0.5 nA
 Focus beam and scan over sample
 big detector as close as possible
 new approach: position sensitive detector
High energy
proton beam
(<1 µA)
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Target plane
Motivation
Why a new PIXE analysis method should be developed?
Requirements defined by geologists:
o fast method to find trace elements (e.g. rare earth elements)
o lateral resolved informations
o large throughput
o big samples
o for grain size determination
o intergrowth analysis, etc.
o to avoid: additional processing steps in mining industry (braking, milling, floating)
 save energy & time
Solution:
novel combination of
 PIXE as analytical method
 position sensitive detector  pixel-detector
 poly-capillary X-ray optics
 fast data acquisition system
 established evaluation software  GeoPIXE
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High-Speed PIXE
Experimental setup
High-Speed PIXE setup
data
acquisition
scanning
system
3–4 MeV protons
SLcam®
beam diagnostic
chamber
sample analysis
chamber
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Experimental setup
How to get lateral & spectral resolved images?
 Particle beam induces divergent X-rays in sample
 Capillaries are collimating and guiding the “right” photons towards the pixels
pixel detector + poly-capillary optics
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 SLcam©
Experimental setup
SLcam®: X-ray Colour Camera
Ø 19 mm
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Pixels
264 x 264 = 69696
Pixels size
48 x 48 µm²
Framerate
400 / 1000 Hz
Sensitive thickness
450 µm
Quantum efficiency
>95% @ 3-10 keV
>30% @ 20 keV
Window
50 µm Be
Lateral resolution
Picture size
Distance to sample
1:1 optics
6:1 optics
50 µm
10 µm
12 x 12 mm²
1.2 x 1.2 mm²
< 10 mm
0.8 mm
Data evaluation
SLcam Imager: real-time data analysis
~5 cm
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Data evaluation
Limits of SLcam Imager
Columbite
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Data evaluation
GeoPIXE: established evaluation software for geological samples
Quantitative evaluation:
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detector properties
sample properties (matrix)
corrections for the optics
X-ray line model
background model
pileup correction
 Deconvolution of spectra
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First results
Lateral resolution:
Measurement of known structure:
67 µm Cu-stripes on Si-wafer
distances: 200/135/67 µm
 intensity distribution along green line
 Gauss-fits at several lines
 lateral resolution ~ 67 µm
(Rayleigh criterion)
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First results
Trace elements:
Geological sample: Cassiterite
measurement time: ~45 Min.
beam current: ~700 nA (3 MeV)
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Prospects & Challenges
 Beam alignment
• homogeneous illumination of samples
• proton yield on samples
 Automation
• movement of samples inside analysis chamber
• integration of optical microscope
• logging of experimental parameters
• logging of radiation doses
• data management
 Calibration
• detector efficiency
• influence of optics
• windowless operation
 Data evaluation
• full integration of GeoPIXE:
 concentration maps in real-time
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Acknowledgement
Johannes von Borany¹
Daniel Hanf¹
Frans Munnik¹
Stanislaw Nowak³
Axel Renno²
Oliver Scharf³
René Ziegenrücker²
¹ Helmholtz-Zentrum Dresden-Rossendorf, Ion Beam Center (HZDR)
² Helmholtz-Institut Freiberg für Ressourcentechnologie (HIF)
³ Institute for Scientific Instruments (IfG)
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Thank
you
for
your
Attention