Nuclear Physics and other Research
Current and next generation experiments in nuclear and particle physics require sensors with fast response and high signal-to-noise ratio for detection of low intensity optical signal. Such photodetectors can be coupled to scintillators for detection and spectroscopy of gamma-rays, charged particles and neutrons.
High performance photodetectors are also required in Cherenkov detectors, liquid xenon and argon detectors for dark matter studies. For several decades, photomultiplier tubes (PMT) have been the key technology for sensing light for most particle physics research operations. Particle physics experiments regularly employ thousands of photomultipliers of many different sizes. PMTs are also used widely in calorimetry and scintillation tracking devices. The key advantage of PMTs in all these applications is their large amplification (~106) with low noise which enables them to achieve high sensitivity for single photoelectron detection.
Although extraordinarily successful, the PMT technology also has a number of limitations: PMTs cannot operate under pressures exceeding a few atmospheres, their sensitivity is limited over a small wavelength band, their optical quantum efficiency is relatively low, they cannot operate under high magnetic fields, they can have some radioactive background, and they are bulky. As a result, there is a real need for alternative photo sensors with fast response, high gain and high signal to noise ratio in many nuclear physics experiments. To overcome the limitations of PMTs in nuclear experiments including scintillation spectroscopy, RMD is exploring a new photodetector technology, silicon photomultiplier (SiPM). A SiPM consists of a large number of micropixels that are joined together on a common silicon substrate and are operated with a common output. Excellent timing resolution (<1 ns-FWHM) has been measured with SiPM at room temperature.