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Factors influencing time resolution in scintillators

Explore factors influencing time resolution in scintillators, aiming for 100ps timing resolution. Develop new biomarkers targeting pancreatic/prostatic cancer using dual modality PET-US probe with high sensitivity. Learn about statistical limits, light transport, rise time importance, and crystal specifications for optimal resolution. Understand the challenges in achieving sub-100ps timing resolution. Our team includes experts from CERN and the Nanotechnology Institute, Lyon.

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Factors influencing time resolution in scintillators

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  1. Factorsinfluencingtime resolutionin scintillators Paul Lecoq CERN, Geneva

  2. Whereis the limit? • Philips and Siemens TOF PET achieve • 550 to 650ps timing resolution • About 9cm localizationalong the LOR • Can weapproach the limit of 100ps (1.5cm)? • Can scintillatorssatisfythis goal?

  3. Development of new biomarkers • First clinicaltargets: pancreatic/prostatic cancer • Tool: dual modality PET-US endoscopic probe • Spatial resolution: 1mm • Timing resolution: 200ps • High sensitivity to detect 1mm tumor in a few mn • Energyresolution: discriminate Compton events

  4. Timing parameters • General assumption , based on Hymantheory • For the scintillator the important parameters are • Time structure of the pulse • Light yield • Light transport • affecting pulse shape, photon statistics and LY decay time of the fast component Photodetector excess noise factor number of photoelectronsgenerated by the fast component

  5. 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 Qth photoelectron td= 40 ns td= 40 ns Nphe=2200 LSO Nphe Nphe Nphe Nphe

  6. Light generation 5d Rare Earth 4f

  7. Factors influencing the scintillation decay time Three important aspects • Dipole and spin allowed transitions • Short wavelength of emission • High refractive index

  8. Light Transport • -49° < θ < 49° Fastforwarddetection 17.2% • 131° < θ < 229° Delayed back detection 17.2% • 57° < θ < 123° Fast escape on the sides 54.5% • 49° < θ < 57° and 123° < θ < 131° infinitebouncing11.1% For a 2x2x20 mm3 LSO crystal Maximum time spreadrelated to difference in travelpathis 424 pspeak to peak ≈162 ps FWHM

  9. Rise time • Rise time is as important as decay time • 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 Qth photoelectron

  10. Time resolutionwithrise time The intensity of light signal of a scintillatingcrystalcanbedescribed by the Shao Formula The number of photo-electrons firing the photo-detector N(t) between 0 and t after simplifications is given by : Arrival time of first photon : Coincidence time resolution CTR :

  11. Photon countingapproach LYSO, 2200pe detected, td=40ns tr=0.5ns tr=1ns tr=0ns tr=0.2ns

  12. Variation of CTR for differentcrystalswithdifferentrise times

  13. Crystal specifications for 200ps CTR Impossible for LuAG:Ce

  14. CoincidenceSiPM-SiPM

  15. Summary of results

  16. Reproducibility LSO vs LSO SiPM Hamamatsu 50mm

  17. Comparisonbetweenpredictions & experimentalresults

  18. Conclusions • Timing resolutionimproveswithlowerthreshold • Ultimateresolutionimplies single photon counting • High light yieldismandatory • 100’000ph/MeV achievablewithscintillators • Shortdecay time • 15-20ns is the limit for brightscintillators (LaBr3) • 1ns achievable but withpoor LY • Crossluminescentmaterials • Severelyquenchedself-activatedscintillators • SHORT RISE TIME • Difficult to break the barrier of 100ps

  19. Our Team • CERN • Etiennette Auffray • Stefan Gundacker • HartmutHillemanns • Pierre Jarron • Arno Knapitsch • Paul Lecoq • Tom Meyer • Kristof Pauwels • François Powolny • Nanotechnology Institute, Lyon • Jean-Louis Leclercq • Xavier Letartre • ChristianSeassal

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