Readout of a 3 m long scintillating fiber by an avalanche photodiode

We carried out an experiment to evaluate the performance of an avalanche photodiode (APD) as a photosensor for a multiclad 3HF scintillating fiber. The scintillating fiber used was 3 m in length and 0.75 mm in diameter. The temperature of the APD was controlled in the range from −50°C to room temperature. The detection efficiency for a minimum ionizing particle traversing the fiber was measured as a function of bias voltage and temperature of the APD. Cooling the APD was essential to clearly distinguish a minimum ionizing particle from noises to exclude. Detection efficiency of nearly 100% was achieved by the APD operated at −40°C or below.