Speaker
Description
Photonic crystals slabs applied to inorganic scintillators
Matteo Salomoni1,3, Rosalinde Pots2,3 , Paul Lecoq3 , Etiennette Auffray3,Marco Paganoni1, Stefan Gundacker1,3, Marco Pizzichemi3, Matthew S. J. Marshall4, Shane Waterman4, Vivek Nagarkar4, Bipin Singh4
1Università degli studi di Milano Bicocca, Piazza dell'Ateneo Nuovo 1, 20126 Milano, Italy
2RWTH Aachen, Templergraben 55, 52062 Aachen, Germany
3CERN, CH-1211, Geneva 23, Switzerland
4RMD, Inc., 44 Hunt Street, Watertown, MA 02472, USA
The extraction of scintillation light from an inorganic scintillator is one of the major bottlenecks in Time-of-Flight Positron emission tomography (ToF-PET) as it directly affects the energy and time resolution of the gamma detector. The most widely used crystal in PET system is LYSO:Ce doped. Having a high index of refraction (IR = 1.82), the amount of light collected to the photo-detector is limited by total internal reflection (TIR): For crystals with high aspect ratios, as the ones used in PET scanners, up to 50% of the scintillation light will not be collected, even if Teflon wrapping and optical coupling are used. Photonic crystal slabs (PCS), defined as thin dielectric layers structured with a 2D or 3D periodic pattern, offer the possibility to increase this efficiency. A higher light output, combined with a reduction of the average path length of the photons in the crystal before their extraction, leads to a more precise evaluation of the particle time detection. This also implies a better coincidence time resolution (CTR). Together these will translate to ToF-PET reconstructed images with a better signal to noise ratio, which will lead to a better diagnosis, faster exams, and the possibility to reduce the patient dose.
For our application, PCS need to be as well as an optical layer that is transparent for the emission spectrum of the LYSO. We have developed the nano-fabrication technology needed to realize the required large nanostructures needed to cover the scintillator readout face. This layer, when applied to the scintillator, helps overcome the TIR due to diffraction effects.
Here we present our work focused on the simulations of the PCS parameters in order to optimize this effects. Using two different simulation tools, GEANT4 and CAMFR, we were able to take into account the geometry and configuration of the crystal to treat (wrapping, coupling, photo-detector, etc.). Optimization has been performed to find the best PCS pattern for a large variety of configurations. For the first time we produced centimeter size specimens patterned fully. We will present the results for LYSO that show a gain in light yield with respect to the same configuration without the PCS. Preliminary results shows also better performances from both the light yield and the timing point of view. In-depth analysis is currently underway. Details on the simulation steps, production process and characterization of the PCS will be presented.
Acknowledgment:
This work was supported in part by the US Department of Homeland Security (DHS), Domestic Nuclear Detection Office (DNDO), under the competitively awarded contract(s) HSHQDC-13-C-B0040, and by European Research Council in the frame of the ERC Advanced Grant TICAL #338953. This support does not constitute an express or implied endorsement on the part of the Government. This work was also supported by the ERC Proof of Concept ULTIMA #680552, and was carried out in the frame of the Crystal Clear Collaboration (CERN).
