1. 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

2. Outline
PIXE fundamentals & Motivation
Experimental setup
Data evaluation & First results
Prospects & Challenges

3. 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)

4. 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:
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

5. PIXE Fundamentals of PIXE: classical micro-beam setup
Object
50x50 μm2
Aperture
1x1 mm2
Lens
Target plane
High-energy
proton beam
(3 µA)
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)
Target plane

6. Motivation High-Speed PIXE
Why a new PIXE analysis method should be developed?
Requirements defined by geologists:
fast method to find trace elements (e.g. rare earth elements)
lateral resolved informations
large throughput
big samples
for grain size determination
intergrowth analysis, etc.
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
High-Speed PIXE

7. Experimental setup High-Speed PIXE setup data acquisition scanning
system
3–4 MeV protons
SLcam®
beam diagnostic
chamber
sample analysis
chamber

8. pixel detector + poly-capillary optics  SLcam©
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  SLcam©

9. Experimental setup SLcam®: X-ray Colour Camera 1:1 optics 6:1 optics
1.2 mm
Ø 19 mm
82 mm
12 cm
Pixels
264 x 264 = 69696
Pixels size
48 x 48 µm²
Framerate
400 / 1000 Hz
Sensitive thickness
450 µm
Quantum efficiency
keV
20 keV
Window
50 µm Be
1:1 optics
6:1 optics
Lateral resolution
50 µm
10 µm
Picture size
12 x 12 mm²
1.2 x 1.2 mm²
Distance to sample
< 10 mm
0.8 mm

10. Data evaluation
SLcam Imager: real-time data analysis
~5 cm

11. Data evaluation
Limits of SLcam Imager
Columbite

12. Data evaluation
GeoPIXE: established evaluation software for geological samples
Quantitative evaluation:
detector properties
sample properties (matrix)
corrections for the optics
X-ray line model
background model
pileup correction
 Deconvolution of spectra

13. First results Lateral resolution: lateral resolution ~ 67 µm
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)

14. First results Trace elements: Geological sample: Cassiterite
measurement time: ~45 Min.
beam current: ~700 nA (3 MeV)

15. 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

16. Thank you for your Attention Acknowledgement Johannes von Borany¹
Daniel Hanf¹
Frans Munnik¹
Thank
you
for
your
Attention
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)