scintillator detector development at isis g. jeff sykora and the isis neutron detector group ikon 8...
TRANSCRIPT
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+