N. Dinu

Temperature and bias voltage dependence of the MPPC detectors

This work reports on the characterization of the Multi-Pixel Photon Counter (MPPC) detectors as a function of the temperature and bias voltage. Devices of 1×1 mm² and 3×3 mm² total area and 50×50 μm² μcell size produced by Hamamatsu Photonics have been studied. The temperature has been varied from −110°C to −50°C using a cryostat cooled by liquid nitrogen and from 0 to 38°C using a climatic chamber. Important electrical parameters of the MPPC detectors as gain, breakdown voltage, quenching resistance, capacitance and dark count rate have been measured.

Characteristics of a prototype matrix of Silicon PhotoMultipliers (SiPM)

This work reports on the electrical (static and dynamic) as well as on the optical characteristics of a prototype matrix of Silicon Photomultipliers (SiPM). The prototype matrix consists of 4 ? 4 SiPMs on the same substrat fabricated at FBK-irst (Trento, Italy). Each SiPM of the matrix has an area of 1 ? 1mm2 and it is composed of 625 microcells connected in parallel. Each microcell of the SiPM is a GM-APD (n+/p junction on P+ substrate) with an area of 40 ? 40 ?m2 connected in series with its integrated polysilicon quenching resistance. The static characteristics as breakdown voltage, quenching resistance, post-breakdown dark current as well as the dynamic characteristics as gain and dark count rate have been analysed. The photon detection efficiency as a function of wavelength and operation voltage has been also estimated.

Development of Intraoperative Beta Probes Based on Silicon Photomultipliers

Intraoperative localization of malignant tissues labeled with positron radiotracers opens up new prospects to improve the efficiency of cancer surgery. Because Silicon Photomultipliers (SiPM) introduced a breakthrough for the development of miniaturized imaging devices, we are currently designing two intraoperative beta probes based on this technology: a light imaging device with a small field of view (~5cm2) to perform tumor localization and post-operative control of the surgical cavity, and a miniaturized counting probe to guide in real time the excision of the tumor lesion. The first step of our project was focused on the characterization and optimization of SiPM devices as photodetectors for intraoperative beta detection. We studied the influence of temperature and bias voltage on the thermal and correlated noises and photon detection efficiency of different SiPM devices. The impact of these two parameters on the overall beta sensitivity was quantified as a function of the intensity of the scintillation light following a simple physical model. According to the results of this comprehensive study, the optimization of the detection head design of the two intraoperative probes was studied using Monte Carlo simulations. Detailed description of the simulation study as well as the performance characterization of the first prototypes will be presented at the conference.