1. DFNA-Ilie Cruceru PERSPECTIVES FOR A POSITRON EMISSION TOMOGRAPHY (PET) PLANT BASED ON RESISITIVE PLATE COUNTER (RPC) Ilie Cruceru, Mihai Petrovici, Florin Constantin, Carmen Nicorescu, Ioana Manea, Mariana Petris, Mircea Ciobanu, Dorin Moisa, Daniela Stanescu National Institute for Physics and Nuclear Engineering “Horia Hulubei”

2. DFNA-Ilie Cruceru General considerations on PET The principles of Positron Emission Tomography (PET) consist in the administration of a radioactive isotope attached to a tracer that persist to reveal its molecular pathways in a human body. A 3-D Complete Body Scan is desired in order to minimize the radiation damage to the patient and to sensitively increase the axial field of view (FOV). From the constructive point of view, a PET set-up has an image converter which consist from a lot of scintillators detectors working in coincidence. These detectors are associated with fast electronics, which assures a coincidence resolution of picosecond order and a good precision in localization of the positron annihilation.

3. DFNA-Ilie Cruceru Detectors employed in PET At the beginning NaI(Tl) scintillators were used for PET. Recently they have been replaced by BGO, CsI(Tl) or CaF. CaF has a time constant of 0.8-5 ns, smaller than the one of NaI(Tl). However, this temporal characteristic is too large for a good resolution in image reconstruction. Spatial and temporal resolution of scintillation detectors is limited from the possibility of construction, chemical composition and crystalline structure. RPC detectors have essential advantages regarding the temporal resolution, spatial resolution compared to the above mentioned scintillators. R&D activities are concentrated in our days to increase their efficiency for electromagnetic radiation.

4. DFNA-Ilie Cruceru RPC mechanical structure The main components of RPC detectors: Resistive glass electrodes Microstrips plate Metallic electrodes Spacers Metallic box Special gas mixture (85% C 2 F 6 H 2, 10% SF 6, 5% C 4 H 10 )

5. DFNA-Ilie Cruceru Figure 1 – General view of RPC detector

6. DFNA-Ilie Cruceru Figure 2 - Experimental set-up

7. DFNA-Ilie Cruceru The main characteristics of RPC detector Detection efficiency larger than 95 % for MIP’s Latest R&D results for electromagnetic efficiency show values < 20% Spatial resolution: -on transversal direction  2 mm -on longitudinal direction < 5 mm Temporal resolution: 70-80 ps Large dimensions: 45  90 cm 2 or larger if necessary

8. DFNA-Ilie Cruceru Figure 3-Detector configuration and block arrangement

9. DFNA-Ilie Cruceru Conclusions From the results of the research and testing performed up to now, we are convinced that RPC detectors are very good candidates for PET applications.