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

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

Detector Usage on ISIS 3He Scintillators Scintillators 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 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 0.14 190-330 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) 260-267 * From Tokuyama Corp.

Basic Detector Operation n + 6Li  4He + 3H + 4.79 MeV Scintillator Light transport Light detector (PMT, SiPM, etc.) “Preamp”/Signal Shaping Signal Processing Discriminator Display/Data Acquisition

Light Collection

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

Scintillator detectors ISIS Scintillator detectors

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 ISIS concept: Minimise light spread Maximise light collection Maximise efficiency PMT A PMT B PMT C PMT D

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

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

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 0.5 - 15Å Ideal application for WLSF detectors A large linear position sensitive WLS fibre scintillation detector array for IMAT 15

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 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!

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

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

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

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

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 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

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

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

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.

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 ) Converter density Neutron detection efficiency Hygroscopicity

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

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

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

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)

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 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