icans-xviii a position sensitive transmission detector for epithermal neutron imaging e. m....
TRANSCRIPT
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ICANS-XVIII
A position sensitive transmission detector for epithermal neutron
imaging
E. M. Schooneveldand
Ancient Charm partners
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Content
∙ Introduction
∙ Principle
∙ Construction
∙ Measurements
∙ Conclusions
∙ Future
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Introduction
∙ ANCIENT CHARM
∙ EU funded FP6 project, contract 015311
∙ Goal: 3D imaging of cultural heritage (archaeological) objects.
∙ Archaeologists want to know elemental and phase composition of object.
∙ Want to look inside object imaging
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∙ Available techniques
∙ Phase, structure texture analysis:
– Neutron diffraction.
∙ Element analysis:
– Delayed Gamma Activation Analysis
(DGAA)
– Prompt Gamma Activation Analysis
(PGAA)
– Neutron Resonant Capture Analysis
(NRCA)
Introduction
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Introduction
∙ Imaging techniques:
– Neutron tomography (NT)
– Neutron diffraction tomography (NDT)
– Prompt Gamma Neutron Activation Imaging
(PGAI)
– Neutron Resonance Capture Imaging (NRCI)
– Neutron Resonance Transmission (NRT)
∙ Our detector transmission neutron detector NRT
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Introduction
∙ Pros:
Native imaging (2D detector) no scanning pencil
beam
“4 solid angle coverage”
Elemental analysis
Structural analysis ?
∙ Cons:
Small dips on high baseline need good statistics +
good baseline estimation
Position resolution limited to ~1mm
Need low beam divergence or detector close to sample
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Principle
Neutron Detector beam
∙ Estimated data collection time: ~1 hr per 2D image ~1 day per tomograph.
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Principle
∙ Element identification by resonant neutron absorption.
∙ Need resonance in right energy range
Neutron absorption resonances of Zn
Neutron energy (eV)
0 200 400 600 800 1000
Cro
ss-s
ecti
on
(B
arn
s)
0
20
40
60
80
100
120
140
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H
Li Be
Na Mg
K
Rb
Cs
Ca Sc V Cr Mn Ti Fe Co Ni Cu Zn
He
B C N O F Ne
Al Si P S Cl Ar
Ga Ge As Se Br Kr
Sr Y Zr Nb Mo (Tc) Ru Rh Pd Ag Cd In Sn Sb Te I Xe
Ba La-Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi (Po) (At) (Rn)
(Ac- Lr)
<10 eV
10 - 100 eV
100 - 1000 eV
1000 - 10000 eV
10000 - 100000 eV
La Ce Pr Nd (Pm) Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Th U (Pa) (Ac) (Np) (Pu)
Lanthanides (Rare Earth elements)
Actinides
(Fr) (Ra) noble gasses
∙ Periodic system with indications for suitability of NRT
(regions were lowest resonance occurs)
Principle
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Construction
∙ Detector
16 channel PMT
Optical fibres(4 per pixel)
GS20 glass scintillators1.8mm * 1.8mm * 9mm
∙ Pixels: 4 * 4 array with 2.5mm pitch 10mm * 10mm active area.
∙ Made 16 pixel prototype to get experience with assembly and test performance.
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Construction
∙ Monte Carlo simulations (GEANT4)
∙ Issues: Type of optical fibre + scintillator support.
∙ Cross-talk:Fibres Support Total cross-talk (%)
- Quartz Quartz Plastic Plastic
Al Al
BoronNitride Al
BoronNitride
12.5 19.4 18.2 28.9 18.3
Made prototype with plastic fibres and BN scintillator support.
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Construction
∙ Photos
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Construction
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Measurements
∙ Measurements on INES beam line at ISIS
∙ DISCLAIMER: Measurements mainly done to examine detector performance (not to demonstrate technique)
∙ Measured a few archaeological objects, but no imaging
∙ Software for composition analysis and image reconstruction not ready yet.
∙ Not enough timing resolution yet.
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No sample (one pixel)
Neutron energy (eV)
1000.0 65.0 29.3 16.6 10.7 7.5 5.5 4.2 3.3 2.7
Co
un
t ra
te (
kHz)
0.0
200.0
400.0
600.0
800.0
TOF (s)
0 100 200 300 400 500 600 700 800 900 1000
Measurements
∙ Basic properties
Useful energy region: up to ~1 keV
Count rate (per pixel): ~200 kHz (5% dead time)
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Measurements
Cross-talk measurement, using a big 20 m thick gold foil with one 2.5*2.5mm hole lined up with a pixel
Neutron energy (eV)
4.0 4.5 5.0 5.5 6.0
Co
un
t ra
te (
A.U
.)
0.0
5.0e+5
1.0e+6
1.5e+6
2.0e+6
2.5e+6
3.0e+6
pixel with goldpixel with hole
∙ “Big” gold foil with 2.5mm hole.
∙ No dip for pixel with hole low cross-talk
As MC predicted plastic fibres no problem
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Measurements
∙ Bronze sheet (90.5% Cu , 8.49% Sn, 0.088% Ag)
∙ Good agreement
∙ Missing peaks, mainly Iodine (upstream in beam)
Measured absorption spectrum of bronze sample
Neutron energy (eV)
0 10 20 30 40 50 60 70 80 90 100
Ab
sorp
tio
n
0.00
0.05
0.10
0.15
0.20
0.25
0.30
measuredtheory
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Measurements
∙ Agreement less good.
∙ Still good for imaging
Measured absorption spectrum of bronze sample
Neutron energy (eV)
200 400 600 800 1000
Ab
sorp
tio
n
0.0
0.2
0.4
0.6
0.8 measuredtheory
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Measurements
∙ Very corroded could not measure tin with diffraction.
∙ Piece of bronze vase from Villa Giulia
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Measurements
No problem to see tin resonances.
Corroded piece of a vase from Villa Giulia.
Neutron energy (eV)
100 150 200 250 300 350 400
Ab
sorp
tio
n
-0.01
0.00
0.01
0.02
0.03
0.04
Tin Copper
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Measurements
∙ ANCIENT CHARM black box
Black box Al 9.
TOF (s)
100 200 300 400 500 600 700 800 900 1000
Co
un
t ra
te (
A.U
.)
0.0
1.0e+4
2.0e+4
3.0e+4
4.0e+4
∙ Diffraction: lot of incoherent scattering
∙ Neutron radiography: low penetration
lot of H}
∙ NRT : much higher penetration of high energy neutrons
hydrogen moderates neutrons peaks broader
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Measurements
Theoretical absorption of 1cm thick silver
Neutron energy (eV)
10 20 30 40 50 60 70 80 90 100
Ab
sorp
tio
n
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Black box Al 9. Spectrum of spot 2
Neutron energy (eV)
10 20 30 40 50 60 70 80 90 100
Ab
sorp
tio
n
-0.1
0.0
0.1
0.1
0.2
0.2
0.3
∙ All peaks about same height thick silver (~1 cm )
∙ Peak amplitudes << 1 background from moderated neutrons.
∙ Peak shape correct still able to identify elements
Black box contains silver object, probably also hydrogen !!
-0.05
0.00
0.10
0.05
0.15
0.20
0.25
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Conclusion
Successfully built 16 pixel prototype transmission detector.
Detector performed very well: Low cross-talk,
high rate
capability,
acceptable energy range.
Successful NRT tests.We are very happy with the detector.
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Diffraction from bronze sample
Neutron wavelength (Å)
0.5 1.0 1.5 2.0 2.5 3.0
No
rmal
ised
co
un
ts
0.75
0.80
0.85
0.90
0.95
1.00
1.05
1.10
Future
∙ 100 pixel detector integrated with goniometer
∙ Imaging
∙ Diffraction
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The end
∙THANK YOU ∙