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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 Bundles

Motivation

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

5-1

0 m

m

10th RD51 Collaboration Meeting, Stony Brook University, USA

Multi-layer converter + THGEM detector

n’

np

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)(1

4A

E

E 22

n

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 MeV

HDPE 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-

Gain

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

PS

F

Simulations Efficiency & Resolution

10-1

100

101

102

103

0

400

800

Energy (keV)

Co

un

ts

100 Conv.

200 Conv.

300 Conv.

Deposited Energy Spectrum Distribution of the deposited charge

Signal

Scattering

Cost effective solution: 300 HDPE layer

Conversion Efficiency ~8%

HD

PE f

oils

Neutrons (2.45 MeV)

Dete

ctor

Vess

el

SSR = Signal-to-Scattering ratio

LayersLayers

Layers LayersLayers

Layers

Parameters-) HDPE Thickness = 0.4 mm-) Gas Gap = 0.6 mm

0 100 200 300 400 500 6000

5

10

15

20

# of Converters

De

t. E

ffici

en

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 Prototypes

Produced using 3D printing technologiesFoils thickness = Gas gap = 0.6 mm

Height = 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 detector

MCNP 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

E

Converter

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