After the gamma photons are transformed into visible photons by scintillation crystal, the low energy photons are converted into electrical signals by photoelectric devices and multiplied and amplified to output scintillation pulse signals.
In the PET system, the low-energy photons converted by scintillating crystals are converted into electrical signals by photoelectric devices, multiplied and amplified, and finally the scintillation pulse signal is output.
Silicon Photomultiplier (SiPM) is a new type of high performance semiconductor photoelectric sensor. Its structure is composed of several identical pixels in parallel. Each pixel is composed of avalanche photodiodes and quenching resistors working in Geiger mode in series. Its function is to detect optical signals and convert them into electrical signals.
It has more advantages compared with traditional photomultiplier tube (PMT) and avalanche photodiode (APD). SiPM has low operating voltage (< 100V), high gain, fast response (ns level), high detection efficiency, compact structure, easy readout and large-scale array fabrication. Each APD unit operates in the counting mode, without gain fluctuation and over noise like linear mode APD, and has better single photon resolution than PMT. It has the potential to replace the traditional photomultiplier tube in the detection of single photon or very weak light signal.
New type of SiPM independently researched and developed by the lab has the characteristics of sub-nanosecond response speed, single photon sensitivity and low noise. The overall performance of the products have reached the international top-ranking level,.
The main performance advantages are:
·ultra-high pulse response speed, pulse rise time as low as 0.88ns.
·Excellent noise performance: TN series SiPM uses high purity silicon crystal material, and based on high precision semiconductor technology, effectively control the number of defects in the material, thereby reducing the dark counting rate (dark counting rate is as low as 88 kHz/mm2); at the same time, optical crosstalk and post-pulse are optimized and enhanced, so excellent overall noise is obtained. Acoustic performance.
·Ultra-high sensitivity, single photon level, with excellent photon counting ability. High gain, internal gain of more than 106, small signal easy to read.
Based on the study of the physical process of the avalanche of SiPM devices, a set of semiconductor avalanche process analysis model is established in this project. For the first time, SiPM devices based on standard CMOS process are realized. A general signal processing and analysis module is developed by combining MVT digital method. It has been successfully applied to radiation detectors, PET detectors and other products.