X-ray Fluorescence Imaging Following Synchrotron Beam ...€¦ · Stanford Synchrotron Radiation...
Transcript of X-ray Fluorescence Imaging Following Synchrotron Beam ...€¦ · Stanford Synchrotron Radiation...
X-ray Fluorescence Imaging FollowingSynchrotron Beam Excitation
April 1-4, 2004 Walters Art Museum Baltimore, Maryland
Uwe Bergmann
Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center
Conference on Applied Digital Imaging Techniques for Understanding the Palimpsest
• introduction to synchrotron radiation (SR)
• x-ray transmission imaging
• x-ray fluorescence (XRF) imaging
• examples of SR based XRF imaging
• details and numbers
• proposed plan
Outline
Synchrotron Radiation Spectrum
• 54 operational light source rings in 19 countries
• 8 rings in construction
• 11 in advanced stages of design/planning
For a list of SR facilities around the world see:
http://ssrl.slac.stanford.edu/SR_SOURCES.HTML
SR Facilities Around the World
Advanced Light Source (ALS), Lawrence Berkeley National Laboratory (1993)
Advanced Photon Source (APS),Argonne National Laboratory (1996)
National Synchrotron Light Source (NSLS)Brookhaven National Laboratory (1982)
Stanford Synchrotron Radiation Laboratory (SSRL)Stanford Linear Accelerator Center (1974)
Four Largest US Synchrotron Sources
Different Types of Synchrotron Sources
schematics of asynchrotron lab
Properties of Synchrotron Sources?
- very intense- tunable- polarization- short pulses
Concept of X-ray Transmission Imaging
0 .9
0 .9 2
0 .9 4
0 .9 6
0 .9 8
1
4 6 8 10 12
Ca F e Z n , 2 µm
Tra
nsm
issi
on
E n e r g y [ k e V ]
- measure transmission at two energies: below and above absorption edge of element of interest
- take difference to enhance contrast
- chemical dependence
plus:
- stereographic imaging is possible- line sources: faster imaging
minus:
- large ink concentration necessary- sample has to be sufficiently transparent to x-rays
Energy (eV)
7120 7140 7160 7180
Nor
mal
ized
Abs
orpt
ion
0.0
0.5
1.0
1.5Fe2O3Fe (acac)3FeCp2FePO4
Fe3+
Fe2+
(a)
7120 7140 7160 71800.0
0.5
1.0
1.5
Fe3+
Concept of X-ray Fluorescence Imaging
valencelevels
3p
2p
1s
Ka1.2
Kß1,3, Kß’
Kß2,5, Kß’’
level diagram Fe
e-
• incident x-ray photon knocks out inner-shell electron• hole is immediately filled from electron in outer shell• fluorescence photon is emitted, predominantly Ka radiation• fluorescence is detected for imaging
plus: greatly enhanced sensitivity compared to transmission imaging
sample
incident x-rays
x-ray fluorescence
fluorescencedetector
x-ray energy
tran
smis
sion
0.9
0.92
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0.98
1
4 6 8 10 12
CCaa FF ee ZZnn, , 22µmmTT
rraannss
mmiiss
ssiioonn
EE nnee rr ggy y [[ kk eeVV ]]
Choice of X-ray Energy
Ca Ka Fe Ka Zn Ka
Investigation of calcifications in breast tissue using EXAFS and XRF
Examples of XRF Imaging with SR
Sayers et al
X-Ray Fluorescence Studies of Elements in Human Lung TissueM.Z. Kiss, D.E. Sayers, A.C. Thompson, S.A. McHugo, P. Pleshanov, E.
Pleshanova1, Yu. A. Bykovsky
Examples of XRF Imaging with SR
100
1000
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2000 4000 6000 8000 1 104 1.2 104
Inte
nsity
/ (5
000
sec)
Energy (eV)
Fe CuAg
Si
hv = 11200 eV
α = 0.085o
Cl
Detection of Trace Impurities
sensitivity to extremely low concentrationsmuch less than millionth of a mono layer!
Baur et al
detector
scanningdirections
X-ray beam from synchrotron
fluorescence from element in ink
z
x
Schematic Experimental Setup
top view
x
polarization
transmissiondetector
palimpsestdetector
x-ray beam
Schematic Experimental Setup
- continuous x-scans- steps in z-direction
example:
10 * 10 cm2 scanning area, 100 µm resolution 1/100 sec illumination per data point 10 seconds/line, 1000 lines~ 3 hours total scanning time
intense x-ray beam is important
front view
x
z
Some Details- scans are performed with high precision computer-controlled translation stages (Huber)
-fast scan ability *
- large area Ge detector for fluorescence detection available
- incident intensity is recorded for normalization
- automated system that closes beam shutter if scanning gets interrupted
- tests on sample texts for best x-ray parameters and potential radiation damage
- palimpsest can be placed in airtight frame (glove box for loading available)
- data analysis programs are available (e.g. Matlab)
blue = available now green = still to be done
Proposed Plan
• build and test all the scanning/imaging hardware • identify one or several elements for imaging (e.g. Fe, Ca) • study a test object of composition similar to the original text • test for appropriate sample protection, X-ray energy, beam size and exposure times (radiation damage)
• study the original text