APD Arrays for Scintillating Fiber Readout

An investigation is underway to determine the feasibility of planar processed, high gain, silicon avalanche photodiode arrays as a readout mechanism for scintillating fibers (SCIFI). Avalanche photodiode (APD) arrays are a compact and rugged alternative to photomultiplier tubes (PMTs). Since SCIFI usually yield a small number of photons compared with bulk scintillators, one goal of this investigation was to determine the photon detection threshold of the APD arrays. A Monte Carlo code was used to simulate a minimum ionizing particle (MIP) interacting with the fiber. The number of photons produced that reach the fiber ends from a MIP was calculated to be between 40-70 photons. The number of photons that reach the fiber ends is dependent on where the MIP interacts along the fiber length, the attenuation length of the fiber, and the fiber length. The next step was to determine the photon detection threshold of an APD array when cooled to -35" C. This was accomplished by using a pulsed LED and a 90Sr beta source. The experimental data show that our APD arrays have a detection efficiency of nearly 100% for photon pulses of >30 photons at a wavelength of 492nm.