2015-02, González Martínez, Antonio Javier, Majewski, Stanislaw, Barbera, J., Conde Castellanos, Pablo Eloy, Correcher, C., Hernández Hernández, Liczandro, Morera, C., Vidal San Sebastián, Luis Fernando, Sánchez Martínez, Filomeno, Stolin, A., Benlloch Baviera, Jose María, Instituto de Instrumentación para Imagen Molecular

In this paper, the capabilities of a wide-area gamma ray photosensor based on a SiPM array are investigated. For this purpose, we have mounted an array of 144 SiPMs with individual active area of mm and a pitch of mm, thus covering an active area of mm. Themeasurements were performed by coupling the SiPM array to LYSO crystal arrays of different pixel size (mm, mm, and mm) and 10-12 mm thicknesses. The SiPM array was controlled by means of three ASICs, and the SiPM signals were multiplexed in order to determine the gamma ray impact position by means of implementing the Anger logic algorithm in the ASIC. The optimum bias voltage and temperature dependence of the gamma ray sensor were determined. An energy resolution as good as 8%, for individual crystal pixels, were reached at 5 V overvoltage. The ASICs design allows one to "activate" different photosensor array areas. This feature has been used to evaluate the detector performance as a function of the crystal pixel size and the photosensor dark noise contribution. In this work we also show the system capability to provide depth-of-interaction (DOI) information by means of implementing a two-layer staggered approach. We have found that accurate DOI information is obtained when the ASICs enabled an SiPM active area as high as mm (SiPMs).

2015-10, Conde Castellanos, Pablo Eloy, González Martínez, Antonio Javier, Gonzalez, A., Hernández Hernández, Liczandro, Bellido, P., Crespo Navarro, Efren, Iborra Carreres, Amadeo, Moliner Martínez, Laura, Rigla Pérez, Juan Pablo, Rodríguez Álvarez, María José, Sanchez, F., Seimetz, Michael, Soriano Asensi, Antonio, Vidal San Sebastián, Luis Fernando, Benlloch Baviera, Jose María, Departamento de Matemática Aplicada, Escuela Técnica Superior de Ingeniería Informática, Instituto de Instrumentación para Imagen Molecular, Ministerio de Ciencia e Innovación, Generalitat Valenciana

In gamma-ray detectors, monolithic scintillation crystals offer the possibility of preserving the scintillation light distribution especially when painted black. The statistical moments of this distribution provide accurate information on the three photon impact coordinates, including their depth of interaction (DOI). Digital SiPMs (dSiPMs) return digital information based on pixels about the collected light distribution, since the signal is a digital sum of the trigger bins. In this work we present, for the first time, an accurate analysis of the statistical moments of the light distribution using monolithic painted black crystals and state-of-the-art dSiPMs. Two 32.6 x 32.6 mm(2) monolithic LYSO crystals covering the entire photodetectors area have been used in coincidence with 10 mm in thickness. The photosensor tiles were kept at a stable temperature of T = 20 degrees C. Energy resolution of about 18% was reached in relation to the zeroth moment. The first moment, related to the impact position, determined a spatial resolution of about 3 mm near the crystal center, but quadratically degrading towards the crystal borders. The DOI resolution, measured by means of the second moment, was found to be nearing 4 mm in the crystal center region. The third order moment, the so-called skewness, is related to the degree of truncation and once calibrated minimizes the compression effects. A corrected spatial resolution of about 3 mm was then measured for the entire crystal surface. DOI resolution improved at the crystal's center, reaching 3.5 mm, but a degradation towards the borders remained due to truncation of the scintillation light distribution.