PSD 7September 2005

Developments and Applications of Gas Based

Neutron Detectors

Introduction

Neutron Detector Characteristics Gaseous Detectors currently in use

Challenges for the future New developments Conclusion

             

N J Rhodes CCLRC ISIS Facility

Neutrons

Provide information on the structure and dynamic of materials on an atomic/molecular scale

Ideal probes for Condensed Matter Research

Zero charge – highly penetrating

Low KE – probe atomic / molecular dynamics(100 eV – sub meV)

Etc…

Non idealised particles for detection

Zero charge – generally weak interaction

Low KE – generally weak interaction

Require a nuclear converter

INTRODUCTION

Cross section at 1 Å

barnes

3He + 1n _______ 3H + 1p - 0.77 MeV 3 000

10B + 1n _______ 7Li + 4He - 2.3 MeV + 0.48MeV 2 100 (93%)

7Li + 4He - 2.7 MeV ( 7%)

6Li + 1n _______ 3H + 4He - 4.79 MeV 520

157Gd + 1n _______ s + Conversion electrons 74 000

natGd + 1n _______ s + Conversion electrons 17 000

Neutron Converters

Neutron ProductionThe ILL

             

ILL 60MW Reactor

Neutron ProductionISIS

SPALLATION NEUTRON SOURCE

Detector Properties

 

             

Detector characteristics for optimisation

Neutron detection efficiency 100 eV – sub meV

Gamma insensitivity 10-6 at 1 MeV

Intrinsic detector background 0.1 c-1 s-1 m-2

Spatial resolution 25 -1 mm2

Speed 1 MHz

Geometry 40 m2

Stability 0.1 % over days

Cost 0 -2 £M

Radiation Hardness gamma and fast n

3He Detector Efficiency

             

Neutron absorption efficiencyfor a 3He filled gastube, 1" diameter,

for various 3He pressures.

Wavelength (Å)

0 2 4 6 8 10Neu

tro

n a

bso

rpti

on

eff

icie

ncy

0.0

0.2

0.4

0.6

0.8

1.0

1 atm 2 atm 5 atm 10 atm

Detector TypesSingle element detectors

             

Chopper spectrometer MARI

900+ detectors - 300 mm long

Molecular spectroscopy TOSCA

Squashed detectors for accurate ΔT

MAPS 1 m long 8 pack detector array

18 channel ADC card

8 channel pre amp

card

Linear PSDsThe MAPS Spectrometer

The MAPS spectrometer

Data Quality truly exceptional

Even some of the simplest structures have revealed complex structures not seen before.

Linear PSDsThe MAPS Detector Array

Linear PSDsMERLIN

2.5m30o2.88m

Sample

3m

INSTRUMENT LAYOUT

DETECTOR ARRAY

3 m long detectors

Detector efficiency (1Å) 70%Gamma efficiency (60Co) 10-8

Intrinsic background 0.16 / pixel / hrSpatial resolution FWHM < 25 mmPulse pair resolution 4 µsArea 21m2

CHARACTERISTICS

No. Detectors No. Packs No. Pixels

280 35 70 000

Requirements

Linear PSDs MERLIN Characteristics

Developments ElsewhereMultitube IN5 ILL

2D PSD LOQ

Ordela 2661N

25% efficient at 1 Å

650 x 650 mm2 active area

5 x 5 mm2 resolution

3He CF4 at 1.5 Bar

2 x 105 rate (10% losses)

             

Brookhaven NLMWPCs

50% efficient at 1.5 Å

1500 x 200 mm2 active area

1.3 x 1.3 mm2 resolution

106 c / s

Brookhaven NLMWPCs

Cylindrical shape to eliminate parallax in one direction.

Developments ElsewhereMWPC D19 ILL

Developments ElsewhereMSGD D20 ILL

Compare characteristics with

the ISIS instrument suite

THE ISIS SECOND TARGET STATION

Schedule

First neutrons 2007

User run starts end 2008

Other sources

ANSTO Australia

SNS USA

FRM-11 Germany

JSNS Japan

Low Energy Transfer Chopper Spectrometer

Detector array

4m high array at 3.5 m radius

-35 to +135 degrees horizontal coverage

Area 40 m2

Position resolution 15 mm FWHM

Energy range 0 – 80 meV

Resistive wire technology

4 m long detectors

Position resolution limited by pre amp

WISH A high resolution magnetic diffractometer

Detector array

~ 1m high array at 2.2 m radius

± 10 to ± 170 degrees horizontal coverage

Position resolution 8 x 8 mm pixels

Wavelength range 1.5 – 15 Å

Large area powder / single crystal diffractometer for the study of magnetic materials

Resistive wire technology

~1500 detectors

1 mm3 crystal 100 kHz per detector

5 mm3 crystal 12 MHz per detector

Resistive Wire TechnologyThe MAPS Detector Array

SANS 2dMWPC

19 m19 m

Active area : 1m x 1m

Position resolution : 5 x 5 mm2

Count rate: 2 x 10 5 n/s at 10% . deadtime

Neutron efficiency: 50% at 2 Å

Commercial solution

Ordela Inc.

Neutron Detector Development in FP6

 

             

Under the EU Framework Programme 6

An Integrated Infrastructure Initiative has been set up for

Neutron Scattering and Muon Spectroscopy

NMI3

includes 8 Joint Research Activities

JRA1 - (DETNI) Detectors for Neutron Instrumentation - Burckhard Gebauer

JRA2 - (MILAND) Millimetre Resolution Large Area Neutron Detector - Bruno Guerard

JRA1 -DETNI

 DETNI: Detectors for Neutron Instrumentation

             

Within DETNI there are three types of detector under development

• Double-sided Si MSD with 157Gd converter

•50 m FWHM, >100 MHz global count rate

• Low pressure MSGD with composite 157Gd/CsI converter

•100 m FWHM, >100 MHz global count rate

• Cascade, a GEM based detector with multiple 10B layers

•1 mm FWHM, >10 MHz global count rate, large areas

Coordinator B. Gebauer HMI-Berlin

GadoliniumDetector Efficiency

             

Neutron absorption efficiency of5m natGd and 2.5m 157Gd foils.

Wavelength (Å)

0 2 4 6 8 10Neu

tro

n a

bso

rpti

on

eff

icie

ncy

0.0

0.2

0.4

0.6

0.8

1.0

Nat 157

JRA1 -DETNI HYBRID MSGD

 

             

B Gebauer et al., HMI Berlin TECHNI and DETNI

JRA1 -DETNI HYBRID MSGD Characteristics

Segmented Delay line readout

Efficiency 1-3 m 157Gd

Position Resolution 0.3 mm FWHM

Rate 2 x 106 c/s/segment

With ASIC for single strip readout

development under DETNI

Efficiency 1-3 m 157Gd

Position Resolution 0.1 mm FWHM

Rate 108 c/s/segment

             

JRA1 -DETNI CASCADEMartin Klein et al., Heidelberg

Neutron Detector Efficiency 40 – 50 % at 1.8 Å (10 GEMs)

Count Rate 107 n cm-2 s-1

Position Resolution 1 – 5 mm

Size 200 x 200 mm2

29% at 1.8 Å, 17% at 1.0 Å

Ar / CO2

JRA2 -MILAND

 MILAND: Millimetre resolution Large Area Neutron Detector

             

Within MILAND there are three types of detector under development

● MWPC ● MSGD ● Gas Scintillation Detector

Coordinator B. Guerard ILL-France

Detection Efficiency: 50% for thermal neutrons aiming for 80%

Area: 320 mm x 320mm aiming for 400 mm x 400 mm

Spatial Resolution: 1 mm x 1 mm

Count rate: 1 MHz global rate at 10% dead time

JRA2 -MILAND

JRA2 -MILAND MWPCs

JRA2 –MILANDMSGDs

JRA2 -MILAND GSPCs

SNSReflectometers

200 x 200 mm detector

1 mm pixel resolution

1.8 – 10.5 Å

Desired Required

Counts / pixel / s 1.3 x 10 6 1.3 x 10 4

Total counts / s 1.2 x 10 8 1.2 x 10 6

Magnetism LiquidsLiquids

MWPCs and MSGDs

Conclusions

Gas detectors have played a vital role in Neutron Detector applications to date.

This will continue in the foreseeable future

Future Requirements

Improvements in position resolution and count rate.

Parallax an issue for some instruments with high resolution and short sample to detector distances.

User friendly, reliable detector electronics is essential

Existing qualities of detectors need to be maintained.

High neutron detection efficiency

low gamma sensitivity

low quiet count

Possibilities for further exploiting these detectors is high