8th thematic workshop: International Symposium On Advanced Intraoperative Imaging of Radioisotopes and Presymposium workshop TOF PET

Scintillators for TOF-PET. What to do?

4 Sept 2009, 11:30

30m

Hotel Baia delle Zagare

Pre Symposium Session 2 : The Role of Scintillators and Photodetectors

Speaker

Paul Lecoq (CERN)

Description

The renewal of interest for Time of Flight Positron Emission Tomography (TOF PET), as well as the necessity to precisely tag events in High Energy Physics (HEP) experiments at future colliders, where high luminosity is achieved through high density trains of bunches are pushing for an optimization of all factors affecting the time resolution of the whole acquisition chain: crystal, photodetector, electronics. The time resolution of a scintillator-based detection system is determined by the rate of photoelectrons at the detection threshold, which depends on the time distribution of photons being converted in the photo-detector. The possibility to achieve time resolution of about 100ps requires an optimization of the light production in the scintillator, the light transport and its transfer from the scintillator to the photodetector. In order to maximize the light yield, and in particular the density of photons in the first nanosecond, while minimizing the rise time and decay time a particular attention must be given to the energy transfer mechanisms to the activator as well as to the energy transition type at the activator ion. A particular emphasis will be put on the light transport within the crystal and the transfer to the photo-detector. Light being produced isotropically in the scintillator the detector geometry must be optimized to decrease the optical path-length to the photodetector. Moreover light bouncing within the scintillator must be reduced as much as possible. It concerns typically about 70% of the photons generated in currently used scintillators. It will be shown how photonics crystals specifically designed to couple light propagation modes inside and outside the crystal at the limit of the total reflection angle can significantly improve this situation and impact on the time resolution. Examples of production and deposition of photonics crystals on LYSO and LuYAP crystals will be shown as well as first results on light extraction improvement.