A novel hermetic detector composed of 200 bismuth germanium oxide crystal scintillators and 393 channel silicon photomultipliers has been developed for positronium (Ps) annihilation studies. This compact 4π detector is capable of simultaneously detecting γ-ray decay in all directions, enabling not only the study of visible and invisible exotic decay processes but also tumor localization in positron emission tomography for small animals. In this study, we investigate the use of a convolutional neural network (CNN) for the localization of Ps annihilation synonymous with tumor localization. Two-γ decay systems of the Ps annihilation from 22Na and 18F radioactive sources are simulated using a GEANT4 simulation. The simulated datasets are preprocessed by applying energy cutoffs. The spatial error in the XY plane from the CNN is compared to that from the classical weighted k-means algorithm centroiding, and the feasibility of CNN-based Ps annihilation reconstruction with tumor localization is discussed.

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A hermetic novel detector composed of 200 Bismuth germanium oxide crystal scintillators and 393 channel silicon photomultipliers has been developed for positronium (Ps) annihilation study. This compact 4π detector is capable of simultaneously detecting γ-ray decay in all directions, enabling not only the study of visible and invisible exotic decay processes but also tumor localization in positron emission tomography for small animals. In this study, we investigate the use of a convolutional neural network (CNN) for the localization of the Ps annihilation synonymous with tumor localization. The 2-γ decay systems of the Ps annihilation from the 22Na and 18F radioactive sources are simulated using GEANT4. The simulated data sets are preprocessed by applying energy cuts. The spatial error in the XY plane from CNN is compared to that from the classical centroiding, weighted k-means algorithm. The feasibility of the CNN-based Ps an-nihilation reconstruction with tumor localization is discussed.

Silicon avalanche photodiode (APD) is a highly sensitive semiconductor photo sensor that uses the photoelectric effect converting light to electric charge. APD has high a gain through avalanche multiplication in its p-n junction. APD also has various preferable characteristics such as high quantum efficiency, large dynamic range, light-weight form-factor, robustness and insensitivity to magnetic fields as well as low light measurement capability thanks to its gain of ~100. As a monolithic device, however, it usually has size of ~5  5 mm 2 . The APD sensor has appealed to various fields of experimental physics due to its low light detection. But its usage is still limited because of its small surface area. The photo sensor in an experiment usually is required to cover a large area. In this study, the pn junction of an APD was simulated with a sufficiently strong electric field enabling avalanche breakdown at ~400 V. We have designed large area APD sensors with channels of 5  5 and 10  10 to cover a wide area of ~5  5 cm 2 . The sensors were fabricated on a 6-inch n-type silicon wafer in about 140 steps. We present the simulation, design and fabrication result for multi-channel silicon APD sensors manufactured in Korea.