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 ∙