A. Denker, W. Bohne, J. Rauschenberg,J. Röhrich, E. Strub ...

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Materials Analysis Using Fast Ions A. Denker , W. Bohne, J. Rauschenberg,J. Röhrich, E. Strub Ionenstrahllabor Hahn-Meitner-Institut Berlin Ionenstrahllabor, Hahn-Meitner-Institut Berlin Introduction: Energy Loss PIXE – Proton Induced X-ray Emission RBS – Rutherford Back Scattering ERDA – Elastic Recoil Detection Analysis

Transcript of A. Denker, W. Bohne, J. Rauschenberg,J. Röhrich, E. Strub ...

Page 1: A. Denker, W. Bohne, J. Rauschenberg,J. Röhrich, E. Strub ...

Materials Analysis Using Fast Ions

A. Denker, W. Bohne, J. Rauschenberg,J. Röhrich, E. Strub

IonenstrahllaborHahn-Meitner-Institut Berlin

Ionenstrahllabor, Hahn-Meitner-Institut Berlin

Introduction: Energy LossPIXE – Proton Induced X-ray Emission

RBS – Rutherford Back ScatteringERDA – Elastic Recoil Detection Analysis

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Ionenstrahllabor, Hahn-Meitner-Institut Berlin

elastic atomic collisions: very low energies typically below a few keV Ion Scattering Spectrometry (ISS)surface composition and structure

inelastic atomic collisions: ionisation of target atomscharacteristic x-ray emission Particle Induced X-ray Emission, detection of elements with Z > 11

elastic nuclear collisions: Rutherford-Back-Scattering – Z > Zion

Elastic Recoil Detection Analysis – Z < Zion

inelastic nuclear collisions: Nuclear Reaction Analysis

Introduction: Ion – Target Interaction

ion

Augerelectron

x-rays

light

backscatteredion

displacedatoms

nuclear reaction products:ions, γ, n

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Ionenstrahllabor, Hahn-Meitner-Institut Berlin

Introduction: Energy Loss

interaction ion – target atoms:⇒ slowing down of the projectiledepends on – ion mass– ion energy– irradiated material

Experimental data, computer software, e.g. SRIM 2003ion and energy Sn

(keV/µm)Se (keV/µm)

range (µm)

lateral straggling (µm)

p, 3 MeV 0.01 20 92 4.1p, 68 MeV 0.001 1.8 21000 860He, 3 MeV 0.17 190 12 0.49197Au, 350 MeV 90 19000 30 0.91

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Ionenstrahllabor, Hahn-Meitner-Institut Berlin

Introduction: Energy Loss

10-3 10-2 10-1 100 101 102 103 104 105101

102

103

104

LindharddE/dx ~ E1/2

BethedE/dx ~ E-1

relativistic

energy transferto electronsenergy transfer

to target nuclei Se Sn Ssum

Stop

ping

Pow

erdE

/dx

(keV

/µm

)

Energy (MeV)

20Ne on Polyethylene

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PIXE – Introduction: History

PIXE = Particle Induced X-ray Emissionfirst observation by Chadwick (Phil. Mag. 24 (1912) 54:x-ray emission induced by charged particles from a radioactive sourceMosely 1913: the energy of the x-rays scales with Z2

first application as today: T.B. Johansson et al, Nucl. Instr. Meth. B 84 (1970) 1412005: widely used technique in archaeology, biology, geology, environmental sciences.....Louvre Museum: dedicated accelerator for ion beam analysis

Louvre

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Ionenstrahllabor, Hahn-Meitner-Institut Berlin

PIXE – Intro: Excitation Possibilities

x-rays from x-ray tube or synchrotron– X-ray fluorescence analysis XRF

electrons– electron microprobe, e.g. in scanning electron microscopes

with ions

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Ionenstrahllabor, Hahn-Meitner-Institut Berlin

PIXE – Intro: Advantages

x-ray tube: larger background due to photon scattering⇒ lower sensitivity

radioactive source, 1 Curie:3 x 107 particles per 1 mm2 per secondrange in Cu ~ 11 µmradio-safety, larger background

accelerator:1013 particles per 1 mm2 per secondrange in Cu for 3 MeV protons: ~ 34 µmbeam can be focussed

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Ionenstrahllabor, Hahn-Meitner-Institut Berlin

0 20 40 60 800.0

0.2

0.4

0.6

0.8

1.0

K Lω

k

Z

PIXE – Basics: Fluorescence Coefficient

hole in K- or L- shellEkin > EB

recombination viaX-ray or Auger electron:fluorescence yield

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Ionenstrahllabor, Hahn-Meitner-Institut Berlin

PIXE – Basics: Moseley Law

• frequency ν = c(Z-1)2 c = 2.48x1015 Hz• ambiguities possible, e.g. Kα As - Lα Pb, both at 10.5 keV

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Ionenstrahllabor, Hahn-Meitner-Institut Berlin

PIXE – Basics: Fine Structure

selection rules:• Δl= ±1• Δj= 0,±1

vacancies in L-shell:possibility of non-radiative transition before x-ray emission(Coster-Kroning effect)

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Ionenstrahllabor, Hahn-Meitner-Institut Berlin

PIXE – Basics: Spectrum

0 10 20 30 60 70 80 90101

102

103

104

Fe Kα

Sn Kα

Sn Kβ

Sn

LαP

b M

Pb Lγ

Sb

Sb

Bi K

α1

Pb

Kβ1

Pb

Kβ2

Sb

LαA

r Kα

Cu

KαP

b Lα

Pb

Pb

Kα2

Pb

Kα1Ep = 66 MeV

I = 0.1 pAt = 200 secDetector: HPGe

Glass I, Amsterdam, End of 16th century Glass II, England (?), End of 17th century

Cou

nts

Energy (keV)

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Ionenstrahllabor, Hahn-Meitner-Institut Berlin

PIXE – Basics: Cross Sections

theoretical calculations:PWBA (Plane Wave Born Approximation)• application of perturbation theory on the transition betweeninitial and final state• initial state:

plane wave projectile and bound atomic electron• final state:

plane wave projectile and electron in continuum

• enhanced: ECPSSR• E = energy loss • C= deviation/deceleration of projectile in Coulomb field• PSS = perturbation of stationary states of the atom by projectile• R = relativistic effects

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PIXE – Basics: Cross Sections

maximum for vp ~ ve

Energy (MeV)

ioni

satio

n cr

oss

sect

ion

(bar

n)

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Ionenstrahllabor, Hahn-Meitner-Institut Berlin

μ

σω ε

=( )

( )Ip a Z Z abs

Y ZN M Z b a

ionisation-cross sections for thin

PIXE – Basics: Cross Sectionssamples:

Y(Z): x-ray yield (counts), peak area of K line

Np: number of projectiles

Ma(Z): target areal density (atoms/cm2)

ωΖ: fluorescence-yield

bz: part of x-rays in the line of interest

εabs: absolute detector efficiency

aµ: absorption of x-rays in the material between placeof x-ray production and detector crystal

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Ionenstrahllabor, Hahn-Meitner-Institut Berlin

PIXE – Practice: Quantitative Analysisnumber of atoms/cm2:

Nt = Y/(Np ωz bz εz 0∫xmax

σz(x)exp(-aµx/sinθ)dx)

Y measured x-ray yieldNp number of projectilesεz, θ angle and detection efficiency

of detectorσz ionisation cross sectionωz fluorescence yieldbz x-rays in line of interestaµ absorption coefficientx range of protons

de-convolution software, e.g. GUPIX, AXIL....

literature/theory

experiment

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Ionenstrahllabor, Hahn-Meitner-Institut Berlin

PIXE – Practice : Absorption and Ranges

attenuation of x-rays inmatterI = I0exp(-µd)

ranges

maximum analytical depth depends on:– matrix– element (x-ray energy) looked for– proton energy

d1/2

(µm)Ca Kα3.6 keV

Pb Lα10.5 keV

Pb Kα1

75 keVin C 78

1.52000 24000

in Cu 4.5 800

3 MeV 68 MeV

in air 140 mm 33 min C 0.75 mm 20 mmin Cu 33 µm 7 mm

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Ionenstrahllabor, Hahn-Meitner-Institut Berlin

PIXE – Practice: Cross Sections

20 30 40 50 60 70 80 90

10-2

10-1

100

101

102

103

104

105

H. Paul At. Data 42 (1989) 105

K ECPSSR L ECPSSR 3 MeV L ECPSSR 66 MeV exp. Values

66 MeVPineda at al. NIM A 299 (1990) 618

Ioni

satio

n C

ross

Sec

tion

(bar

n)

Z

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Ionenstrahllabor, Hahn-Meitner-Institut Berlin

PIXE – Practice: Experimental Set-up

in vacuum:

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Ionenstrahllabor, Hahn-Meitner-Institut Berlin

PIXE – Practice: Experimental Set-up

2 Lasers

ionisation-chamber

(< 0.1 pA)

HPGet~200s

shielding

objecton

x-y table

protons

in air:

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Ionenstrahllabor, Hahn-Meitner-Institut Berlin

Zyklotron k = 132

1 613

1211

53 2

410

14

9

16

8

715

ECR-Quelle und 5.5 MV-Van de Graaff

Augen - Tumor - Therapie

PIXE Practice: ISL- Accelerators and target areas

PIXE68 MeVFeb. 05:

> 550 Patients

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PIXE – Practice: Detector

SemiconductorsSi(Li) = Li doted Si, up to EX ~ 25keV, resolution 160eV at 5.9 keVpriceHPGe = high purity Ge, above EX ~ 3 keVresolution 180 eV at 5.9 keV

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Ionenstrahllabor, Hahn-Meitner-Institut Berlin

PIXE – Practice: Spectrum

O. Schmelmer, PhD Thesis, 2001 Energy (keV)

Ep = 16 MeV

coun

ts

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Ionenstrahllabor, Hahn-Meitner-Institut Berlin

PIXE – Practice: Spectrum Background

AB: Atomic Bremsstrahlung = deceleration of bound target electrons in the Coulomb field of the projectileSEB: Secondary-Electron-Bremsstrahlung = Bremsstrahlung of electrons from ionisation processes

Emax = 4me/Mp x Ep

QFEB:Quasi-free electron-Bremsstrahlung

Emax = me/Mp x Ep

Compton:inelastic scattering of γ-rays from nuclear reactions with the electrons in the detector crystal

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both reports based on art historical expertiseindirect dating: identification of pigments

(Cr in green: after 1850)

report 1 (Japan):

500 years old1 Mio. €

report 2 (Berlin):

100 years oldmax. 25 000 €

20 c

mPIXE – Example: Chinese Bowl

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Ionenstrahllabor, Hahn-Meitner-Institut Berlin

PIXE – Example: Chinese Bowl

porcelain extremely sensitive high-energy protons: small risk ofdamage due to low proton intensity andsmall dE/dx

on bowl:Pb (flux)Cu (pigment)no Cr

modern porcelain:Cr (pigment)

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PIXE – Example: Chinese Bowl

green colour no informationyellow colour measured:Zn and Fe, no Sbabsence of Sb isindication for age:after ~1850

⇒ report 2 could beconfirmed

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PIXE – Example: Prussian Medal

Prussian Medal, about 1790 Deutsches Historisches Museum, Berlinmassive object?gilded?t = 200s, Ip ~0.1 pAresult:

medal: Lα/Kα = 1.09

1 µm Au-foil:Lα/Kα ~ 40,

~ 75% Au~ 15% Ag~ 10% Cu

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Rutherford Back Scattering - RBS: Principleconservation of energy and momentum⇒ univocal identification of target atom(thin samples)energy loss ΔE in target:thickness determinationdetectable elements:Z > Zion

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RBS – example: Light Ions contra Heavy Ions

Eion = kp E0

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Elastic Recoil Detection Analysis - ERDA: Principle

detection of recoiled atomsidentification by simultaneous measurement of energy and, e.g. time-of-flightcomparable sensitivities for all elements (hydrogen enhanced by a factor of 4)

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coincident measurement of energy + time-of-flight for the outscatteredatoms of the sample(large dynamic range in energy (depth) due to TOF method)using cyclotrons:time structure of ion beamsmall emittance

ERDA: Experimental Set-Up

Si-energy-detector, 24 stripeslarge solid angle (1.6 msr)

two large channel-plate time-of-flight detectors

flight path: 120 cm

sample

ions

only absolute, standard free method for the concentration of all elements in thin layersirradiation of the sample with heavy high energetic ions e.g. 197Au 350MeV

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ERDA: example

example: Ti/Al multilayeron steel5 double layers of 150 nm Al and 100 nm Ti

Page 33: A. Denker, W. Bohne, J. Rauschenberg,J. Röhrich, E. Strub ...

Ionenstrahllabor, Hahn-Meitner-Institut Berlin

Conclusion I

ERDA RBS PIXE NRAsensitivitydepends on matrix and element looked for

• ppm for H• 10 ppm for

others

• ppm for heavy elements

• 0.1% for light elements

ppm–

0.1%

100 ppm

depth resolution

10 nm close to surface

10 nm close to the surface

1 – 10 µm 5 nm close to surface

max. analytical depth

a few µm a few µm up to a few mm

a few µm

elements all Z > Zion Z > 11 15N(H,α)12C......

Page 34: A. Denker, W. Bohne, J. Rauschenberg,J. Röhrich, E. Strub ...

Ionenstrahllabor, Hahn-Meitner-Institut Berlin

Conclusion II

various ion – target interactions ⇒ vast choice of different techniqueseach technique:specific advantages and drawbacksbest answers to analytical problems:careful choice of analytical technique or combination of techniques, e.g. RBS + PIXEtoday: estimated 1000 accelerators world-wide used for ion beam analysissamples: