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Abstract-A new type of silicon device has been realized that has many properties comparable to, or better than, a conventional PMT (Photomultiplier Tube). This paper presents the first results of using these photodetectors in place of a PMT in the readout of scintillators for possible PET (Positron Emission Tomography) applications. This device, the Silicon Photomultiplier (SiPM), is effectively an avalanche photodiode operated in Geiger mode. In Geiger-mode detectors, a very large current signal is produced regardless of the size of the input, giving just logical rather than proportional information. However, the SiPM is subdivided into a large number (1440) of microcells that act as independent and virtually identical Geiger-mode photodiodes. The outputs of all these individual microcells are connected so that the total output signal is the sum of the signals from all of the microcells that were activated. In this way proportional information can be obtained. As a consequence of their design, these detectors have potentially very fast timing, high gain (10 5 10 6 ) at low bias voltage ( 50 V), a high quantum efficiency (35% at 500 nm), excellent single photoelectron resolution and are cheap to manufacture. Here we present results obtained with this new photodetector when used with pulsed LED and scintillator pixels.

A new type of silicon device has been realised that has many properties comparable to or better than a conventional PMT (Photomultiplier Tube). This paper presents the first results of using these devices in place of PMT for the readout of scintillators for eventual application in PET (Positron Emission Tomography). This device, the Silicon Photomultiplier (SiPM) is effectively an avalanche photodiode operated in Geiger mode. In Geiger-mode detectors, a very large current signal is produced regardless of the size of the input, giving just logical rather than proportional information. However, the SiPM is subdivided into a large number (1500) of microcells that act as independent and virtually identical Geiger-mode photodiodes. The outputs of all these individual microcells are connected so that the total output signal is the sum of the signals from all of the microcells that were fired. In this way proportional information can be obtained. As a consequence of their design, these detectors have potentially very fast timing (<100ps), high gain (10 5 -10 6 ) at low bias voltage (~50V), a high quantum efficiency (35% at 500nm), excellent single photoelectron resolution and are cheap to manufacture. Here their characterisation and initial results when used with pulsed LED and scintillator pixels are presented.

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