P. Lecoq CERN 1March 2014 Fast timing workshop, Clermont Fd, March 12-14, 2014

Ultimate Time Resolution in

Scintillator-based detectors for

Calorimetry and Time-of-Flight PET

P. Lecoq, E. Auffray, S. Gundacker

CERN, Geneva, Switzerland

This work is supported under the ERC Grant Agreement N°338953–TICAL

P. Lecoq CERNMarch 2014 2Fast timing workshop, Clermont Fd, March 12-14, 2014

TOF for– Particle ID– Pileup mitigation at high luminosity colliders

Improve pattern recognition in Cerenkov detectors Cerenkov/Scintillation differentiation (Dual Readout Cal) Bring additional information on the shower development

in a segmented calorimeter Current state of the art for TOF in Alice expt: 75ps Major advances in detector/enabling technologies

– Fast and high light yield scintillators– SiPMs, MCPs– Fast low noise FE electronics (NINO)

A 4D imaging HHCAL is within reach

Why fast timing in HEP?

P. Lecoq CERNMarch 2014 3Fast timing workshop, Clermont Fd, March 12-14, 2014

Why fast timing in PET? TOF for rejecting background events (event collimation)

– Requires 200ps TOF resolution for a few cm ROI (EndoTOFPET-US FP7 project)

TOF for improving image S/N– Requires 100ps TOF resolution for x5 S/N improvement, which

brings a potential sensitivity gain (dose reduction)

TOF for direct 3D information– Requires 20ps TOF resolution for 3mm resolution along LOR

TOF for restoring image quality for limited angle tomography

P. Lecoq CERNMarch 2014 4Fast timing workshop, Clermont Fd, March 12-14, 2014

State of th Art: CTR with NINO chip (Time over Threshold)

P. Lecoq CERNMarch 2014 5Fast timing workshop, Clermont Fd, March 12-14, 2014

Influence of crystal length on CTR

S. Gundacker et.al., NIMA, dx.doi.org/10.1016/j.nima.2013.11.025

P. Lecoq CERNMarch 2014 6Fast timing workshop, Clermont Fd, March 12-14, 2014

• CTR distribution of 168 Modules (4x4 cells each) , 2688 LORs• The bias voltage applied to each module is fixed to 2.5 Volt over breakdown

Voltage.• Same threshold and temp for all channels

State of the art: EndoTOFPET system performance

239 ps

NINO ASIC

4x4 cells3.5x3.5x15mm3

crystals80mm 3M ESR gap

Discrete Silicon-through-via

(TPV) MPPC arrayHamamatsu (S12643-

050CN)3x3mm2, 0.6mm gap

To be compared to ≈ 550(350) ps

on commercial systems

P. Lecoq CERNMarch 2014 7Fast timing workshop, Clermont Fd, March 12-14, 2014

The detection chain

q2

SiPMCrystal electronics

g

Dt

tkth pe = Dt

Conversion depth

+ tk’ ph

Scintillation process

+ ttransit

Transit timejitter

+ tSPTR

Single photon time spread

+ tTDC

TDC conversion time

Random deletion 1Absorption

Self-absorption

Random deletion 2SiPM PDE

Unwanted pulses 2DCR

Unwanted pulses 1DCR, cross talk

Afterpulses

P. Lecoq CERNMarch 2014 8Fast timing workshop, Clermont Fd, March 12-14, 2014

Modeling the whole chain

SiPM

S. GundackerThesis, CERN,

Feb2014

P. Lecoq CERNMarch 2014 9Fast timing workshop, Clermont Fd, March 12-14, 2014

Analog vs Digital approachCramer-Rao lower bound

Under investigation – in the frame of the FP7 EndoTOFPET-US project– with the Philips digital evaluation kit recently ordered

S. GundackerThesis, CERN,

Feb2014

P. Lecoq CERNMarch 2014 10Fast timing workshop, Clermont Fd, March 12-14, 2014

Parameters of interest to improve timing resolution

CTR improves like SQRT (photon time density)

Rise time influence limited by SPTR (66ps)

Parameters for LSO: Ce, Ca and Hamamatsu S10931-050P MPPC

P. Lecoq CERNMarch 2014 11Fast timing workshop, Clermont Fd, March 12-14, 2014

Factors influencing scintillator time resolution

Besides all factors related to photodetection and readout electronics the scintillator contributes to the time

resolution through:1. The scintillation mechanism

Light yield, Rise time, Decay time

P. Lecoq et al, IEEE Trans. Nucl. Sci. 57 (2010) 2411-2416

2. The light transport in the crystal Time spread related to different light propagation modes

3. The light extraction efficiency (LYLO) Impact on photostatistics Weights the distribution of light propagation modes

P. Lecoq CERNMarch 2014 12Fast timing workshop, Clermont Fd, March 12-14, 2014

Influence of prompt photons

2x2x3mm3 LSO:Ce, Ca with 70ps rise timeand an arbitrary number of prompt photons generated

P. Lecoq CERNMarch 2014 13Fast timing workshop, Clermont Fd, March 12-14, 2014

Light generation in scintillators

Rare Earth4f

5d

P. Lecoq CERNMarch 2014 14Fast timing workshop, Clermont Fd, March 12-14, 2014

Wide emission spectrum from UV to IR

Ultrafast emission in the ps range

Independant of temperature

Independant of defects

Absolute Quantum Yield Whn/Wphonon = 10-8/(10-11-10-12) ≈ 10-3 to 10-4 ph/eh pair

Higher yield if structures or dips in CB? Interesting to look at CeF3

Hot intraband luminescence

More details in SCINT2013 paper TNS-00194-2013M. Korzhik, P. Lecoq, A. Vasil’ev

P. Lecoq CERNMarch 2014 15Fast timing workshop, Clermont Fd, March 12-14, 2014

Photon propagation time spread

xL

€

Dt prop max = nxc cos(θ1)

− (2L − x) nc cos(θ 2)

with q1 0 q2 qc

For L = 20mm LSO (n = 1.82)ngrease= 1.41 qc = 50.8°

q2

Dtmax= 71 ps for x = LDtmax= 384 ps for x = 0

Photodetector

g

P. Lecoq CERNMarch 2014 16Fast timing workshop, Clermont Fd, March 12-14, 2014

Photonic crystals

Crystal

Crystal- air interface with PhC grating:

θ>θc

Total Reflection at the interface Extracted Modeθ>θc

Nanostructured interface allowing to couple light propagation modes inside and outside the crystal

air

θ>θc

P. Lecoq CERNMarch 2014 17Fast timing workshop, Clermont Fd, March 12-14, 2014

Use large LYSO crystal: 10x10mm2 to avoid edge effects

6 different patches (2.6mm x 1.2mm) and 1 (1.2mm x 0.3mm) of different PhC patterns

0° 45°

Photonic crystals increase the light extraction efficiency

A. Knapitsch et al, “Photonic crystals: A novel approach to enhance the light output of scintillation based detectors, NIM A268, pp.385-388, 2011

P. Lecoq CERNMarch 2014 18Fast timing workshop, Clermont Fd, March 12-14, 2014

Regular LYSO

a)

Extract more photons at first incidence with PhC

= better timing

b)

Photonic crystals compress the light propagation modes

P. Lecoq CERNMarch 2014 19Fast timing workshop, Clermont Fd, March 12-14, 2014

Conclusions

Standard scintillation mechanisms are unlikely to give access to the 10ps range

A number of transient phenomena could generate ps measurable signals

Photonic crystals improve scintillator timing resolution by two means:– By increasing the light output and therefore decreasing the

photostatistics jitter– By redistributing the light in the fastest propagation modes

in the crystal