New Approaches to Improve Timing Resolution in Scintillators

The future generation of radiation detectors is more and more demanding on timing performance for a wide range of applications, such as time of flight (TOF) techniques for PET cameras and particle identification in nuclear physics and high energy physics detectors, precise event time tagging in high luminosity accelerators and a number of photonic applications based on single photon detection. A detailed analysis of the factors limiting timing resolution in scintillators is presented. Several solutions are proposed to overcome these limitations assuming the photodetector and the readout electronics are not the limiting factors. On the scintillator side both the light production and the light transport are addressed. The light production timing parameters are driven by three factors: relaxation time of hot electron-hole pairs; creation of excitons and their trapping on luminescent centers; and strength of the luminescent center transition matrix element. The opportunity to make use of Cerenkov emission and to reactivate research lines on cross-luminescence and more generally on interband luminescence, as well as on populating a high carrier density donor band is discussed. A particular emphasis is put on the possibilities offered by quantum confinement. On the side of light transport a better understanding of the statistical distribution of optical photons at the photodetector is building-up progressively. Different approaches to make use of this knowledge are proposed, such as photonic crystals, single photon counting techniques and light channeling in metamaterials.