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10th RD51 Collaboration Meeting, Stony Brook University, USA
Progress in Fast-Neutron THGEM Detector for Fan-Beam Tomography
ApplicationsM. Cortesi1,2, R. Zboray1, R. Adams1,2, V. Dangendorf3, A. Breskin4 and H-M Prasser1,2
1. Paul Scherrer Institute (PSI), Villigen PSI, CH-5232 Switzerland2. Eidgenössische Technische Hochschule Zürich (ETHZ), CH-8092 Switzerland3. Physikalisch-Technische Bundesanstalt (PTB), D-38116 Braunschweig,
Germany 4. Weizmann Institute of Science (WIS), Rehovot 76100, Israel
10th RD51 Collaboration Meeting, Stony Brook University, USA
Fluid dynamic studies in BWR Fuel Rod BundlesMotivation
10th RD51 Collaboration Meeting, Stony Brook University, USA
ICON beam line, SINQ at PSI, Switzerland:Example: Imaging using cold neutrons
Double subchannel + spacer inside:
neutron guide tube
multiphase outlet
scintillator screen
air-water inlets, turn table
FOV 6.5*6.5cm
double subchannel
(Zboray et al. Nucl. Eng. Des. 241 pp.3201)
More penetration depth Fast Neutron
10th RD51 Collaboration Meeting, Stony Brook University, USA
Goal: Fast-Neutron TomographyDetector Requirements:• Good time resolution (ns range)• High Counting rate (MHz/cm2
range)• Good spatial resolution (mm
scale)• High Detection Efficiency (few
%)• Large area (m2)
1D High-Efficiency Fast-Neutron Imaging Detector
TwoFast Project:• Multiple fast-n point sources (e.g. D-D fusion, 2.5 MeV)• Ring-shaped Fast-Neutron
detector
detector ring
phantom
(G)APD matrices
Plastic converter +(THGEM) as 2D fast neutron detector
Plastic scintillator +(G)APD matrix
In this presentation
D-D pulsed neutron generator
RF-driven Plasma ion source
Multiple point source sequentially pulse
10th RD51 Collaboration Meeting, Stony Brook University, USA
2D Imaging with neutrons
Fast/Cold Neutron 2D radiography
2 mm pitch, 1.35ns/mm
• 2x 10x10cm2 THGEM• 2-sided pad-string anode • Delay-line readout (SMD)
Ionization electrons are multiplied & localized in cascaded-THGEMs imaging detector. -) Detection efficiency: < 0.1%(fast-n) ~ 5% (cold-n) -) Spatial Resolution ~ 1 mm -) Counting Rate ~ 1 kcps/cm2
7Li/4He
10th RD51 Collaboration Meeting, Stony Brook University, USA
High Efficiency Detector
…….+ + +Neutron Neutron Neutron
resistive layer on insulatorRead-out
2D radiography: for efficiency need to cascade many detectors!
100 detector elements for efficiency ≈ 6%
1D radiography 2D cross-sectional tomography
1 detector for efficiency ≈ 10%
Neutron source
Projectional image 1D distribution of neutron attenuation inside the object,
integrated over projection chords
5-10 mm
10th RD51 Collaboration Meeting, Stony Brook University, USA
Multi-layer converter + THGEM detector
n’n
p
2D Readout Board
Antistatic HDPE layer (no charging up)
THGEM1
THGEM2
ΔV
E
Detector Concept:• n scatter on H in HDPE-radiator foils, p escape the foil. • p induce e- in gaseous conversion gap.• e- are multiplied and localized in THGEM-detector.• Combine several 1D radiographs 2D cross sectional tomography.
Detector design:-) Foils thickness (2.5 MeV neutron)-) Gas gap thickness (Deposited Energy)-) Converter height (Axial resolution)-) Number of converter foils (Detector Length)
Detector Performances:-) Spatial Resolution -) Efficiency of transport e- in small gap-) Detector Efficiency
Cortesi et al. 20012 JINST 7 C02056
10th RD51 Collaboration Meeting, Stony Brook University, USA
Simulation Converter Thickness
Impinging neutron
(En)
θ
Scattered neutron
Target
Recoiled nucleus
(ER) θcos
A)(14A
EE 2
2n
R
Escaped protons (GEANT4)
For 2.45 MeV Neutron impinging on HDPE layer:-) Max. Efficiency ≈ 0.06%-) Effective Conversion length = 100 μm-) Broad Spectrum (0 2.5 MeV)
Target Max. Ener. Tran. σ(2.45 MeV)1H 100% 2.5 MeV ~2.55 b12C 28.4% 0.7 MeV ~1.6 b
HDPE (C2H4 – Mass Density = 0.93 g/cm3)
0 40 80 120 160 2000.000
0.025
0.050
0.075
0.100
Recoil Protons Efficiency
Det
ectio
n ef
ficie
ncy
(%)
HDPE thickness (m)
Neutron 2.5 MeVHDPE density = 0.93 g/cm3
MCNPX calculation
Effi
cien
cy (%
)
MCNP calculated energy spectrum of escape protons
HDPE
Range of 2.5 MeV protons
Escape protons
Fraction of interaction neutrons
Energy (MeV)
10th RD51 Collaboration Meeting, Stony Brook University, USA
Simulation Deposited Energy in the Gas
Geant4 Simulation snapshot
n n’
p
δe-
t d
HDPENe/5%CH4 (1 atm)
1 mm
MPV~ 2.7 keV (~ 75 e-)
Gas Gap = 0.6 mm
0 500 1000 1500 2000 250010-1
101
103
105
107
X-Rays Limit
Ar/CH4(5%)
X-Rays Limit Ne/CH4(23%)
Ne/CH4(5%)
Effec
tive-G
ain
VTHGEM(Volt)
Ne
1 atm gas Flow modeCsI + UV Light
X-Rays Limit
X-Rays Limit
single THGEM (t = 0.8, d = 0.5, a=1mm, rim = 0.1 mm)
Gain
Cortesi et al. 2009 JINST 4 P08001
Broad Spectrum of Energy deposited by
recoil proton
Larger dynamic range in Ne-Mixtures
10th RD51 Collaboration Meeting, Stony Brook University, USA
-50 -25 0 25 50
10-4
10-3
10-2
10-1
100
101
Position (mm)N
orm
aliz
ed P
SF
Simulations Efficiency & Resolution
10-1
100
101
102
1030
400
800
Energy (keV)
Cou
nts
100 Conv.200 Conv.300 Conv.
Deposited Energy Spectrum Distribution of the deposited chargeSignal
Scattering
Cost effective solution: 300 HDPE layer
Conversion Efficiency ~8%
HDPE
foils
Neutrons (2.45 MeV)
Dete
ctor
Ves
sel
SSR = Signal-to-Scattering ratio
LayersLayersLayers Layers
LayersLayers
Parameters-) HDPE Thickness = 0.4 mm-) Gas Gap = 0.6 mm
0 100 200 300 400 500 6000
5
10
15
20
# of Converters
Det
. Effi
cien
cy (%
)
0 100 200 300 400 500 6000
2
4
6
8
10
SN
RS
SR
Cortesi et al. 20012 JINST 7 C02056
10th RD51 Collaboration Meeting, Stony Brook University, USA
Converter PrototypesProduced using 3D printing technologies
Foils thickness = Gas gap = 0.6 mmHeight = 6 mm, 10 mmMaterial Antistatic ABS
• 2x 10x10cm2 THGEM• 2-sided pad-string anode • Delay-line readout (SMD)
Cortesi et al. 2007 JINST 2 P09002 6 mm height converter
10 mm height converter
10th RD51 Collaboration Meeting, Stony Brook University, USA
e- Collection Efficiency Vs Electric Field
Full Collection efficiency above 0.4 kV/cm in the Converter Gas
Gap
Gas Ne/CF4 (1 atm)Detector Gain ~ 103
X-Rays
Side-Irradiation with soft (5.9 keV)
X-Rays
MCNP Snapshot
10th RD51 Collaboration Meeting, Stony Brook University, USA
Electric Fields (Converter-Drift) Tuning
Field Ratio = Drift / Converter
Focusing of the ionization electron transferred from the converter Gas Gap to the Drift Gap (THGEM hole pitch ≠ Converter Foils
pitch Drift Gap)
Full transfer efficiency for field ratio > 2:1Ideal values: (1kV/cm Drift Field, 0.5 kV/cm Converter Field)
1.2 mm
1 mm
THGEM
Converter
New THGEM Configuration hole pitch
= Foils pitch(No drift Gap)
NEXT
10th RD51 Collaboration Meeting, Stony Brook University, USA
Electron Transport through the (0.6 mm) gas gap
6-10 mm
3.2 mm
2-cascade THGEM Detector:-) Effective area 10x10 cmConverter Prototypes geometry:-) Foils Thickness = 0.6 mm-) Gas Gap = 0.6 mm-) Converter Height = 6mm / 10 mm-) number of foils = 83
Transport efficiency - Methodology: -) “Top” irradiation with soft (5.9 keV X-rays)-) Comparison between the spectra of Deposited Energy (MCNP) and measured Pulse-Height Spectra using the THGEM detectorMCNP calculated spectra of deposited energy
6 mm height Converter
Measured Spectra
10th RD51 Collaboration Meeting, Stony Brook University, USA
Electron Transport through the (0.6 mm) gas gap
6-10 mm
3.2 mm
2-cascade THGEM Detector:-) Effective area 10x10 cmConverter Prototypes geometry:-) Foils Thickness = 0.6 mm-) Gas Gap = 0.6 mm-) Converter Height = 6mm / 10 mm-) number of foils = 83
Transport efficiency - Methodology: -) “Top” irradiation with soft (5.9 keV X-rays)-) Comparison between the spectra of Deposited Energy (MCNP) and measured Pulse-Height Spectra using the THGEM detector
6 mm height Converter
Measured Spectra
Electron Transport Efficiency Converter-to-Drift Counts Rate ratios = MCNP/Measured (full efficiency
= 1)MCNP calculated spectra of deposited energy
10th RD51 Collaboration Meeting, Stony Brook University, USA
Efficiency ≈ 92%
Deposited Energy (MCNP) Measured Spectra
Efficiency ≈ 30%
6 mm height Converter
10 mm height Converter
Significant loss of Efficiency due to
charging up of the foils &/or secondary
effects(Distorted converter field)
Electron Transport through the (0.6 mm) gas gap
Small Efficiency loss due to electron
diffusion
10th RD51 Collaboration Meeting, Stony Brook University, USA
Transport Efficiency (Garfield simulation)
2D Readout Board
100 electron per event simulated in the gas gap
at various height (2-8 mm)
THGEM1
THGEM2
EConverter
Detected Event at least one electron focused in the THGEM hole
for 6 mm height Aver. Transport efficiency = 95% (≈ measured efficiency soft X-rays)------------------------------------------
for 10 mm height Aver. Transport efficiency = 70% (> measured efficiency soft X-rays) Charging up!
Charge lost due to electron diffusion!
10th RD51 Collaboration Meeting, Stony Brook University, USA
Detection Efficiency (fast neutron)2.5 MeV neutron induced recoil proton in 0.6 mm Gas Gap MVP = 2.7 KeV
Detected Event at least one electron focused in the THGEM hole
6 mm height converter: Aver. Transport efficiency = 97%
-) Conversions efficiency ≈ 8% for ~300 foils-) Transport Efficiency ≈ 97% for 6 mm height, 0.6 mm gas gap-) Discrimination threshold (front-end electronics) ≈ 90%
Estimated Fast-n Detection Efficiency ≈ 7%
10th RD51 Collaboration Meeting, Stony Brook University, USA
Summary & Future Plan Goal TWO-FAST: Fast neutron tomographic 2D cross-sectional images
Main Application: non-destructive testing for the nuclear energy industry: multi-phase flow, spent nuclear fuel bundles inspection, safeguards …
Others: detection of SNM, explosive (border control), material science …
Two Detector technologies Feasibility study Gaseous Detector (THGEM)
New Idea many n-to-p converters, single 2D Detector readout
* Expected detection efficiency ~7% (300 foils) * 1D Radiography, spatial resolution ~ 1 mm * Low sensitivity to gamma background
* 10x10 cm2 imaging detector prototype ready for neutron with antistatic HDPE multi-layers converter produced using 3D printing Converter thickness = Gas gap ≈ 0.6 mm (83 layers) * Improvement of charge-readout electronics * Implementation with TWO-FAST compact D-D generator
10th RD51 Collaboration Meeting, Stony Brook University, USA
1. Emitting spot size: Ø2mm
Burning plasma in the RF-driven ion source with external antenna
Compact, pulsed neutron generator
2.45 MeV
TWOFAST: Fast imaging with fast neutrons, feasibility study
Cooperation: Prof. Ka-Ngo Leung, Berkeley
3. Nominal yield: 108 neutrons/s
2. Pulsed operation: 1kHz; D.F.:1-10%
High fraction (>90%) mono-atomic plasma