Development of the first petalo prototype and sipm studies for neutrino physics

Resumen

Positron Emission Tomography (PET) is a non-invasive technique with provides functional images of metabolic processes occurring in the body. A radiotracer doped with a positron emitter isotope is injected into the patient’s body and is accumulated in the area to be studied. There the positron is annihilated with an electron of the environment and give rise to two back to back gammas. The detection of the two gammas in coincidence allows us to infer the position of the annihilation and, therefore, to reconstruct three-dimensional images showing the metabolic processes happening in the body. In this work, we discuss in depth the potential of the PETALO (Positron Emission TOF Apparatus based on Liquid xenOn) project, which is a new concept in the field of medical imaging aiming to demonstrate that liquid xenon (LXe) together with a SiPM-based readout and fast electronics, provide a significant improvement in PET-TOF technology. Liquid xenon allows for a continuous medium with a high stopping power for 511-keV gammas as well as a uniform response avoiding most of the geometrical distortions of conventional detectors based on scintillating crystals. In addition, SiPMs enable a fast and accurate measurement of the energy with a small noise contribution at the low temperatures required from LXe. Results on the simulations for a full body PET scanner are presented: the energy resolution achieved is 7.85% FWHM and from the reconstructed coordinates, resolutions of 1.5 mm for the r coordinate and 1 mm for both phi and z were obtained for point-like events. The coincidence time resolution (CTR) obtained in our simulated detector is 60 ps for point-like events without including the fluctuations from jitter and the electronics. These results reveal the potential of the PETALO technology and suggest that refinements in the SiPM and ASIC technologies as well as the improvements in point-like events selection could lead to a boost in the current PET technology. The initial phase of the PETALO project is being dedicated to the demonstration of the detector concept using the PETit prototype. It consists of an aluminum box with a unique volume of LXe and two planes of SiPMs that register the scintillation light emitted in xenon by the gammas coming from a Na22 radioactive source and two PTFE pieces in front of each sensor plane to create small xenon volumes coupled to each SiPM. After some months of data taking, PETit has already measured an excellent energy resolution of Rm = 4.2% ± 0.2% FWHM using scintillation light only. This leads to an inferred liquid xenon intrinsic energy resolution compatible with zero with an upper value of 0.4% FWHM (at 95% CL). In the final part of this work, a detailed study of the SiPMs to be used in the neutrinoless double beta decay NEXT-100 detector and their properties was carried out. It was concluded that the sensors and the cables present good performance, great stability, low noise and, hence, they are suitable for NEXT-100.