ICANS-XVIII A position sensitive transmission detector for epithermal neutron imaging E. M. Schooneveld and Ancient Charm partners.
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ICANS-XVIII
A position sensitive transmission detector for epithermal neutron
imaging
E. M. Schooneveldand
Ancient Charm partners
Content
∙ Introduction
∙ Principle
∙ Construction
∙ Measurements
∙ Conclusions
∙ Future
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
∙ 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
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
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
Principle
Neutron Detector beam
∙ Estimated data collection time: ~1 hr per 2D image ~1 day per tomograph.
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
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
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.
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.
Construction
∙ Photos
Construction
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.
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)
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
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
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
Measurements
∙ Very corroded could not measure tin with diffraction.
∙ Piece of bronze vase from Villa Giulia
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
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
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
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.
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
The end
∙THANK YOU ∙
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