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

0.94

0.96

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

104

105

106

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