Scintillator Detector

Development at ISIS

G. Jeff Sykora

and the ISIS Neutron Detector Group

IKON 85 Feb 2015

Detector R&D at ISISThe R&D lines

Scintillator Detectors Scintillator Light Collection Light Detection Mechanics Electronics Signal Processing

3He based detectors Gas mixture Mechanics Electronics Signal Processing

Non 3He based detectors Evaluation of 10B

coated straw tubes

Imaging Detector Converter Readout chips Signal

Processing

Detector Usage on ISIS

3He 15 instruments 0 proposed

Scintillators 14 active instruments 1 in construction 2 proposed

Scintillators 3 muon instruments

Why not just stick with 3He?

Fun to work with new things

Some applications are easier to achieve using other methods

Form factors may suit other methods

3He crisis

6Li Containing Inorganic Scintillators

C.W.E. van Eijk, A. Bessière, P. Dorenbos, Inorganic thermal-neutron scintillators, Nucl. Instr. Meth. A 29 (2004) 260-267

Host Dopant Density (g/cm3)

Photons per Neutron

Photons per MeV

Gammaα/β Ratio λem (nm) τ (ns)

6Li-Glass Ce 2.5 6000 4000 0.3 395 75

6LiF/ZnS Ag 2.6 160,000 75,000 0.44 450 100, >10,000

6LiI Eu 4.1 50,000 12,000 0.87 470 1400

LiBaF3 Ce,K 5.3 3500 5000 0.14 190-330 1/34/

6LiGd(11BO3)3 Ce 3.5 40,000 25,000 0.32 385, 415 200/800

Cs26LiYCl6 Ce 3.3 70,000 22,000 0.66 255/380 3/1000

Cs26LiYB6 Ce 4.1 88,000 23,000 0.76 389, 423 89/2500

* 6LiCaAlF6 Ce 3.0 290 40

* 6LiCaAlF6 Eu 3.0 30,000 370 1,150

* From Tokuyama Corp.

Basic Detector Operation

Light detector(PMT, SiPM, etc.)

Light transportScintillator

“Preamp”/Signal Shaping

Signal Processing

DiscriminatorDisplay/Data Acquisition

n + 6Li 4He + 3H + 4.79 MeV

Light Collection

Light CollectionDirect View Light Guide

Clear Optical Fibre Wavelength Shifting Fibre

SCINTILLATOR DETECTORS

ISIS

Current 6LiF/ZnS:Ag detectors

Problems Limited light collection geometries Difficult assembly Huge number of fibres Limited to large photocathode PMTs

6LiF/ZnS:Ag WLSF Detector Principles

PMT A

PMT B

PMT C

PMT D

Neutron counts per area (cm2) per second for KEK2 and Megan2Irradiation in moderated 241AmBe source NDF R2 G11A bay 1April 2011

Threshold, mV

0 200 400 600 800 1000 1200 1400

counts/cm

2/s

0

20

40

60

80

Average count rate per unit area

ISIS concept:Minimise light spread

Maximise light collection

Maximise efficiency

80% of 3He tube

Detector performance – 1st generation detector

Neutron detection efficiency 80% of 1 inch, 6 bar 3He tube at 1.8 Å

~65% efficient at 1.8 Å

Gamma sensitivity at 200mV Sensitivity to 137Cs gamma ~3x10-9

Sensitivity to 60Co gamma ~3x10-7

Uniformity at 200mV ± 5.5%

Multi-counting <0.1% Local peak rate capability

16kHz per PMT

Note: Neutron detection efficiency, rate capabilityand gamma sensitivity measured at RID

General Powder Diffraction

Linear PSD

2-5mm position resolution

~1 m linear coverage

Good uniformity

Good gamma discrimination

0.5 – 6 Å range

Linear Detector with Multi-anode PMTs

16ch MAPMTs Back end electronics 9 x 1mm fibres per pixel or 36 x 0.5mm fibres per pixel Implications for all future

detectors

Optical cross-talk on the PMT!

2D Graph 2

Spectrum

0 10 20 30 40 50 60

No

rma

lised C

oun

ts

0.7

0.8

0.9

1.0

1.1

1.2

1.3

OriginalWith cross-talk removal

2D Graph 9

LLD, mV

0 200 400 600 800 1000 1200 1400

Cou

nts/se

c/cm2

0

20

40

60

80

Original - MAPMT Demo detectorCross-talk removal - MAPMT Demo detectorReference detector

PEARL beam line detector at RID based on this technology.

Diffraction – With TextureIMAT:

Imaging and MATerials Beam Line

Diffraction detectors up to ~18m2

4 mm x 100 mm resolution

90 degree bank 4.5 m2

Wavelengths 0.5 - 15Å

Ideal application for WLSF detectors

Working detector for IMAT? 90 degree bank

Good performance ~40,000 fibres

Compared to ~1M clear optical fibres

Only Linear PSD Wrap 10,000 elements

individually

IMAT – Continuous scintillator

Optical cross-talk from the geometry!

High degree of optical isolation Fibre bends ~2.5mm radius

Minimum dead space

Various PMT choices Single anode 16/64 channel MAPMT

2D Graph 10

LLD, mV

0 200 400 600 800 1000 1200 1400

Co

un

ts/sec/cm

2

0

20

40

60

80

100

Original - Cont ScintillatorCross-talk removal - Cont ScintillatorReference detector

63% thermal neutron detection efficiency

Reduced light collection

IMAT – Venetian Scintillator

2D Graph 1

Wavelength, Angstrom

2 4 6 8 10

Ra

tio

0.5

1.0

1.5

2.0

2.5

Col 1 vs Col 2

High degree of optical isolation Fibre bends ~2.5mm radius

Minimum dead space

Various PMT choices Single anode 16/64 channel MAPMT

70% thermal neutron efficiency

Better light collection More difficult to assemble

Venetian counts/Flat sheet counts

IMAT – Crossed Fibre High degree of optical isolation Continuous scintillator Various PMT choices

Single anode 16/64 channel MAPMT

Good light collection Easy to assemble 45% thermal neutron

detection efficiency (4-fold coincidence)

R&D on wall thickness

2D Graph 2

LLD, mV

0 200 400 600 800 1000 1200 1400

Cou

nts

/sec

/cm

2

0

10

20

30

40

50

60

4 Fold coincidence2 Fold coincidence

IMAT – Crossed Fibre High degree of optical isolation Continuous scintillator Various PMT choices

Single anode 16/64 channel MAPMT

Good light collection Easy to assemble 65% thermal neutron

detection efficiency R&D on wall thickness

2D Graph 1

LLD, mV

0 200 400 600 800 1000 1200 1400 1600

Co

un

ts/s/cm2

0

10

20

30

40

50

60

70

Reference4 Fold original processing4 Fold new processing

Reflectometers

Linear PSD

0.5mm position resolution preferable

~300 mm linear coverage

Good uniformity

0.5 – 15 Å range

High rate capability preferable

Large dynamic range

0.5 mm linear PSDReflectometers

Max count rate = 16kHz per PMT

Continuous scintillator and MAPMTs

0.7mm FWHM resolution

Signal processing algorithm reduces ghosting

Normalized spectra for WLSF S1=0.7, S2=0.35

WLSF FWHM straight through = 1.3 pixels = 0.65 mmf=y0+a*exp(-.5*((x-x0)/b)^2)

pixel #

290 295 300 305 310 315 320

Count rate

, counts/Am

pH

0

500

1000

1500

2000

Straight through peakFit

Single Crystal Diffractometers 2D Reflectometer

and GISANS 1 x 1mm2 acceptable 0.5 x 0.5mm2 preferable Varying areas/angular coverage 0.5 – 15 Å range Large dynamic range

LMX

Larmor

2D Crossed fibre

1.2mm resolution

Continuous scintillator and MAPMTs 1mm fibres on 1mm pitch Coded: 96 MA-PMT pixels (768 fibre ends) Unusual design: 3 layers 2*X + 1 Y

5.1mm

2.0mm

Inelastic Neutron Scattering

Current: Resistive Wire technology

Large area 2D – 25 mm position resolution Energy range 0 – 80 meV Good uniformity High efficiency Low background

3He Replacement Detector Large Area INS

8x8 array of 20mm x 20mm pixels 1 x 16ch MAPMT Continuous scintillator Crossed fibre 5mm fibre pitch

2D Graph 3

LLD, mV

0 200 400 600 800 1000 1200 1400

Counts/sec/cm

2

0

20

40

60

80

100

120

140

Original Cross-talk reduction Reference detector

~65% thermal neutron detection efficiency

± 5% uniformity with cross-talk reduction

Quiet counts still high (~30x 3He tube)

Biggest Challenges Rate Capability

New Scintillator Faster Fibre New Signal Processing

Background Signal processing Clever readout ????

J-Parc – ISIS collaboration

Now Pushing the Limits of Scintillator Detector TechnologyFor Neutron Scattering!

TRUST-LiCAF Tokuyama Corp.

Summary

Still have significant challenges to overcome.

2D position determination algorithms for fine resolution detectors

Rate capability → New fibres/arrangements - scintillators - signal

processing

Background counts for inelastic spectrometers

Wavelength shifting fibre detectors are versatile.

There are now several options for the IMAT 90 degree bank.

Simplifying assembly does not hinder detector performance.

Further improvements can still be made.

64 channel flat panel PMTs

Thank You!

Important Properties Light yield (typically in photons/MeV for gamma or

photons/neutron) Scintillation efficiency

Emission (and absorption) spectra Light detection

Decay time Count rate capability n/γ pulse shape discrimination

α/β ratio n/γ discrimination

Density and atomic number (ρZ4eff )

n/γ discrimination Converter density

Neutron detection efficiency Hygroscopicity

Gamma (only) Sensitivity• 137Cs (0.662 MeV - 600MBq)• 60Co (1.22 MeV average - 5.1MBq)

Example: GS-20Glass Scintillator

• Beam monitors

• High rate/low gamma environment detectors

2D Graph 1

Pulse height, V

0.0 0.5 1.0 1.5 2.0

Co

unts/seco

nd

0.0

0.5

1.0

1.5

2.0

2.5

Counts vs Counts/s

Neutrons

Gamma

GS20 directly coupled to a PMT in an 241AmBe source

10B containing Neutron Scintillators

10B usually used in plastic or liquid scintillators ZnS:Ag (10B2O3) – Newly developed

LiB3O5 and Li2B4O7 High density Boron Nitride

Ceramic

Cross-talk reduction on Billy 128

∙ Large dip

with wide

spread in the

amount of

cross-talk

∙ Dip has been

much reduced

and there is

now very

little spread

PEARL vs Billy128

∙ Performance of first 64 scintillators

∙ Counting uniformity for threshold of 200

∙ Variations < ±16%

Very acceptable uniformity

We tested only the first half of the detector, because the (old) discriminator can read out only 32 PMT pixels (2 PMTs)

Element to element variation

∙ Variation from element to element is now 5% from

the mean!

Aside: Factors Influencing Decay Time

• Fluorescence and phosphorescence • Speed of energy transfer• Number of luminescence centers

– More centers = faster decay• Impurities (electron or hole traps)

– Shallow traps will temporarily hold charges– Some scintillators are also storage phosphors

ZnS:Ag decay from alpha excitation

ZnS decay time is rarely quoted the same:

~100 ns

~1000 ns

~10000 ns

Why? Afterglow confuses the situation!

e-

Eg

h+