P. Lecoq CERN2 February ENVISION WP2 Meeting CERN Group contribution to ENVISION WP2 Paul Lecoq CERN, Geneva

P. Lecoq CERN 2 February ENVISION WP2 Meeting Objectives of our group Understand the ultimate timing limitations in photodetection systems and reach the best possible timing performance –Biomedical imaging (TOF-PET, FLIM…), HEP (Cerenkov…)

P. Lecoq CERN 2 February ENVISION WP2 Meeting 3 TOF-PET detection system Scintillator –LSO, LYSO, LuAG:Ce or Pr, LaBr3, other crystals –Size and shape effects –Light transport (photonic crystals) Scintillator Photodetector Readout Electronics  rays 511 keV X-rays keV currentvoltage tt Scintillator Photodetector –Vacuum: PMT, MCP –Solid state: APD, SIPM Readout electronics –NINO (Time based) –HPTDC

P. Lecoq CERN 2 February ENVISION WP2 Meeting Where is the limit? Philips and Siemens TOF PET achieve –550 to 650ps timing resolution –About 9cm localization along the LOR Can we approach the limit of 100ps (1.5cm)? Can scintillators satisfy this goal?

P. Lecoq CERN 2 February ENVISION WP2 Meeting For the scintillator the important parameters are –Time structure of the pulse –Light yield –Light transport affecting pulse shape, photon statistics and LY Timing parameters decay time of the fast component Photodetector excess noise factor number of photoelectrons generated by the fast component General assumption, based on Hyman theory

P. Lecoq CERN 2 February ENVISION WP2 Meeting Light output: LYSO example Statistics on about 1000 LYSO pixels 2x2x20mm 3 –produced by CPI –for the ClearPEM-Sonic project (CERIMED) Mean value = ph/MeV For 511 KeV and 25%QE: 2378 phe Assuming ENF= 1.1 Nphe/ENF ≈ 2200 phe

P. Lecoq CERN2 February ENVISION WP2 Meeting  = 40 ns N phe  = 40 ns N phe Statistical limit on timing resolution W(Q,t) is the time interval distribution between photoelectrons = the probability density that the interval between event Q-1 and event Q is t = time resolution when the signal is triggered on the Q th photoelectron LSO N phe =2200

P. Lecoq CERN 2 February ENVISION WP2 Meeting Light generation Rare Earth 4f 5d

P. Lecoq CERN 2 February ENVISION WP2 Meeting Effect of rise time LYSO, 2200pe detected,  d =40ns  r =0ns  r =0.2ns  r =0.5ns  r =1ns

P. Lecoq CERN 2 February ENVISION WP2 Meeting Light Transport –-49° <  < 49° Fast forward detection 17.2% –131° <  < 229° Delayed back detection 17.2% –57° <  Fast escape on the sides 54.5% –49° <  < 57° and 123° <  < 131° infinite bouncing 11.1% For a 2x2x20 mm 3 LSO crystal Maximum time spread related to difference in travel path is 342 ps peak to peak ≈142 ps FWHM

P. Lecoq CERN 2 February ENVISION WP2 Meeting Photonic crystals to improve light extraction Periodic medium allowing to couple light propagation modes inside and outside the crystal M. Kronberger, E. Auffray, P. Lecoq, Probing the concept of Photonics Crystals on Scintillating Materials TNS on Nucl. Sc. Vol.55, Nb3, June 2008, p %34%

P. Lecoq CERN 2 February ENVISION WP2 Meeting PhC very preliminary results LSO crystal 2.8mm 1.3mm 0.6mm 100x100  m 2 10  m 2.5  m

P. Lecoq CERN 2 February ENVISION WP2 Meeting PhC very preliminary results

P. Lecoq CERN 2 February ENVISION WP2 MeetingConclusions Timing resolution improves with lower threshold Ultimate resolution implies single photon counting High light yield is mandatory –100’000ph/MeV achievable with scintillators Short decay time –15-20ns is the limit for bright scintillators (LaBr 3 ) –1ns achievable but with poor LY Crossluminescent materials Severely quenched self-activated scintillators SHORT RISE TIME –Difficult to break the barrier of 100ps