SiPM Photomultipler Scintillator Detectors

What are the advantages and disadvantages of using SiPM (silicon photomultiplier) instead of PMT in scintillation detectors?

SiPM, Silicon Photomultiplier, sometimes also called MPPC (multi-pixel photon counter), is a kind of solid-state semiconductor light sensor, different from PMT, which operates based on the vacuum photoelectric effect. 

The most basic unit of SiPM consists of an Avalanche Photodiode (APD) in Geiger mode and a series quenching resistor, which together form a pixel. A silicon photomultiplier is the combination of numerous such micro-sized pixels arranged in a 2-dimensional array. The Geiger mode means the bias voltage of the APD is higher than its breakdown voltage. In the Geiger mode, even with very weak input light, output saturation (Geiger discharge) will occur in the APD.  A quenching resistor is connected in series with the APD. The function of the quenching resistor is to automatically reduce the bias voltage and thus quickly stop avalanche multiplication in the APD, making the pixel recovered for detection of the next incoming photon again. This enables the detection and amplification of weak light signals.

The working principle of the SiPM scintillator detector is as follows: The scintillator first convert radiations into photons. When a pixel in a silicon photomultiplier (MPPC; SiPM) receives an incident photon, it will be triggered and produce a pulse of a certain amplitude. When multiple pixels receive incident photons, these pulses from each pixel will eventually be superimposed and output from a common output terminal. In a silicon photomultiplier, the amplitude of the aggregate sigal is proportional to the number of pixels triggered. This is why SiPM will have a saturation problem under a strong photon flux, as there is only a limited number of pixels in the cell.

While in a PMT scintillator detector, this is what happens: The scintillator fluorescence, when irradiated, when the photocathode of the PMT is illuminated, releases photoelectrons due to the photoelectric effect. The generated electrons enter the multiplication stage, achieving continuous multiplication and amplification of the electrons. Finally, a current signal is output through the anode.

Compared to the traditional method of using PMT (photomultiplier tubes) as the readout for scintillation detectors, the advantages of using SiPM readout scintillation detectors include:

1. More compact and flexible, suitable for integrated and lightweight design. For small to medium active areas, SiPM-based detectors have a lower cost.
2. Much lower voltage supplies and power consumption than PMTs. While PMTs usually require thousands of volts, the required voltage of SiPM scintillator detectors can be as low as 30-60V
3. SiPM (Silicon photomultipliers) are solid-state photodetectors, making them more rugged and resistant to vibrations and shocks. Furthermore, they are almost not sensitive to magnetic fields, which means magnetic shields are not needed as in the case of using PMT based scintillation detector
4. SiPM scintillation detectors are usually configured with the bias and preamplifier modules that compensate for temperature-induced gain drift, thus stabilizing the signal

The limitations of SiPM scintillation detectors are:

1. Signal-to-noise ratio (SNR): Both PMT and MPPC can detect single photons. However, because MPPC has a higher dark count rate, PMT has the best signal-to-noise ratio for detecting very weak light.
2. In an SiPM, the number of pixels that are hit with photons determines the amplitude of the aggregate pulse output. When the number of incoming photons exceeds the number of pixels in the cell, the SiPM becomes saturated, and the response becomes non-linear.
3. Detection area: PMTs are the first choice for large-area applications. While SiPM Silicon photomultipliers are generally miniature in size, and needs to be connected into a matrix for large-area applications.
4. Dark count rate: SiPM scintillation detectors need temperature compensation measures because their dark count rate increases with temperature.
5. Response speed: The response speed of photodetectors is usually quantified using the rise time or maximum usable count rate. PMT has the fastest response, while MPPC is slower.

Shalom EO-reliable supplier of SiPM photomultiplier scintillation detectors

Shalom EO supplies scintillation detectors based on SiPM. We provide custom scintillation detectors consisting of scintillators+SiPM. Flexible custom solutions of tailored geometries and designs are available. The scintillation detectors Shalom EO offers are compact size, robust and stable, immune to magnetic fields, and have low voltage requirements for the voltage suppliers. The SiPM photomultiplier scintillator detectors are excellent for applications like Positron Emission Tomography, physic experiments.

Different types of scintillation crystals can be selected.

FAQ: When should I choose SiPM photomultiplier scintillation detectors

• Nuclear medical imaging (e.g., PET, SPECT) and monitoring of radioactivities, where smaller sizes and flexible integration are preferred
• Suitable for industrial and field detectors and portable measuring instruments
• When the scintillator does not require a very large area for the photodetector
• When the budget is limited

Below is a drawing of Shalom EO's SiPM photomultiplier scintillator detector: