1. Scintillator Detector and the ISIS Neutron Detector Group
Development at ISIS
G. Jeff Sykora
and the ISIS Neutron Detector Group
IKON 8
5 Feb 2015

2. Detector R&D at ISIS The 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

3. Detector Usage on ISIS 3He Scintillators Scintillators 15 instruments
0 proposed
Scintillators
14 active instruments
1 in construction
2 proposed
Scintillators
3 muon instruments

4. 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

5. 6Li Containing Inorganic Scintillators
Host
Dopant
Density (g/cm3)
Photons per Neutron
Photons per MeV Gamma
α/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
1/34/
6LiGd(11BO3)3
3.5
40,000
25,000
0.32
385, 415
200/800
Cs26LiYCl6
3.3
70,000
22,000
0.66
255/380
3/1000
Cs26LiYB6
88,000
23,000
0.76
389, 423
89/2500
* 6LiCaAlF6
3.0
290 40
30,000
370
1,150
C.W.E. van Eijk, A. Bessière, P. Dorenbos, Inorganic thermal-neutron scintillators, Nucl. Instr. Meth. A 29 (2004)
* From Tokuyama Corp.

6. Basic Detector Operation
n + 6Li  4He + 3H MeV
Scintillator
Light transport
Light detector
(PMT, SiPM, etc.)
“Preamp”/Signal Shaping
Signal Processing
Discriminator
Display/Data Acquisition

7. Light Collection

8. Light Collection Direct View Light Guide Clear Optical Fibre
Wavelength Shifting Fibre

9. Scintillator detectors
ISIS
Scintillator detectors

10. Current 6LiF/ZnS:Ag detectors
Problems
Limited light collection geometries
Difficult assembly
Huge number of fibres
Limited to large photocathode PMTs

11. 6LiF/ZnS:Ag WLSF Detector Principles
ISIS concept:
Minimise light spread
Maximise light collection
Maximise efficiency
PMT A
PMT B
PMT C
PMT D

12. Detector performance – 1st generation detector
80% of 3He tube
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 capability
and gamma sensitivity measured at RID

13. General Powder Diffraction
Linear PSD
2-5mm position resolution
~1 m linear coverage
Good uniformity
Good gamma discrimination
0.5 – 6 Å range

14. 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!
PEARL beam line detector at RID
based on this technology.

15. Diffraction – With Texture IMAT: Imaging and MATerials Beam Line
Diffraction detectors up to ~18m2
4 mm x 100 mm resolution
90 degree bank 4.5 m2
Wavelengths Å
Ideal application for WLSF detectors
A large linear position sensitive WLS fibre scintillation detector array for IMAT 15

16. 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

17. IMAT – Continuous scintillator
High degree of optical isolation
Fibre bends ~2.5mm radius
Minimum dead space
Various PMT choices
Single anode
16/64 channel MAPMT
63% thermal neutron detection efficiency
Reduced light collection
Optical cross-talk from the geometry!

18. IMAT – Venetian Scintillator
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

19. 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

20. 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

21. 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

22. 0.5 mm linear PSD Reflectometers
Continuous scintillator and MAPMTs
0.7mm FWHM resolution
Signal processing algorithm reduces ghosting
Max count rate = 16kHz per PMT

23. 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

24. 2D Crossed fibre 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
1.2mm resolution
5.1mm
2.0mm

25. Inelastic Neutron Scattering
Large area
2D – 25 mm position resolution
Energy range 0 – 80 meV
Good uniformity
High efficiency
Low background
Current: Resistive Wire technology

26. 3He Replacement Detector
Large Area INS
8x8 array of 20mm x 20mm pixels
1 x 16ch MAPMT
Continuous scintillator
Crossed fibre
5mm fibre pitch
~65% thermal neutron detection efficiency
± 5% uniformity with cross-talk reduction
Quiet counts still high (~30x 3He tube) 26

27. Now Pushing the Limits of Scintillator Detector Technology
Biggest Challenges
Rate Capability
New Scintillator
Faster Fibre
New Signal Processing
Background
Signal processing
Clever readout
????
Now Pushing the Limits of
Scintillator Detector Technology
For Neutron Scattering!
J-Parc – ISIS collaboration
TRUST-LiCAF Tokuyama Corp.

28. 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

29. Thank You!

30. 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 )
Converter density
Neutron detection efficiency
Hygroscopicity

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

32. Example: GS-20 Glass Scintillator
GS20 directly coupled to a PMT
in an 241AmBe source
Beam monitors
High rate/low gamma environment detectors
Neutrons
Gamma

33. 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

34. 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

35. Performance of first 64 scintillators
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)

36. Element to element variation
Variation from element to element is now 5% from the mean!

37. 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 e- Eg h+
ZnS decay time is rarely quoted the same:
~100 ns
~1000 ns
~10000 ns
Why? Afterglow confuses the situation!
ZnS:Ag decay from alpha excitation