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Gamma Spectroscopy with Silicon Photomultiplier SiPM MicroFC 60035 SMT and CsI(Tl) scintillation crystal

MicroFC-60035-SMT manufactured by Sensl is 6x6mm SiPM silicon photomultiplier sensor. The C series 60035 has P-on-N type structure and used for blue range light, that's why it fit perfectly CsI(Tl) scintillation crystal. I made a prototype project that plugged into computer audio card and it works as an amateur gamma spectroscopy detector. The prototype board has bias voltage converter for SiPM with negative output of -30V. And it has pulse amplifier to make the signal compatible with 192kHz audio card input. To read out the SiPM from the standard output, the photocurrent generated on detection of photons needs to be converted into voltage. That task can be achieved using a transimpedance amplifier (TIA).


The circuit is powered with one 9V battery. It power up automatically when TRS 3.5mm cable is plugged into the socket. Using SiPM for gamma spectroscopy has pros and cons. The price for SiPM is approximately equal to a classic photomultiplier tube. But the active area of 6x6mm limits the maximum size of an applicable crystal for gamma spectrometry. That's why if you are looking for high performance spectroscopy system with a big crystal then SiPM is not the choice. However it can be used in miniature constructions where you can compromise for efficiency and resolution. 

Because SiPM require low voltage bias of ~30V in contrast with 1000V for classic photomultiplier tube, it also can be additional advantage for an amateur simple project. If you follow all design recommendation published by Sensl and if you make correct calculation and adjustments for TIA then you can end up with pretty good resolution and acceptable linearity for the SiPM detector. My sample has FWHM% resolution <7.3% on Cs-137 662keV. It can be used to collect gamma spectra in range of 32keV-3000keV.

The overall performance of the detector is good, in my opinion. Even the SiPM little bit noisy on low energy, but the size and weight of the whole construction makes it attractive same as a classic vacuum tube detectors.



Big disadvantage of non-compensated SiPM detector is the gain drifts caused by the temperature changes. 

During the temperature drops from 44.4C to 8.5C the Eu-152 1408keV peak shifted to about 463 channels up. The resolution, noise level and SiPM amplification improved as temperature goes down. As expected, the semiconductor behaves better with lower temperature. But that huge drifting for channels is not acceptable for portable instrument, and even not for laboratory testing due to day and night temperature changes. 


Small prototype board was assembled to resolve that problem, based on the previous circuit but with hardware correction added for temperature's changes. With the correction, the channels drift was fixed over same temperature range. You can see at high temperature (red line) it still has more noise and resolution degradation, however all channels stay at the same position. That make great difference for long-term spectrum stability and portable usage of SiPM based devices. 



If you want to order SiPM driver board with bias voltage and temperature correction for MicroFC60035 then please check my product: USB Gamma Spectrometer Audio ADC for MPPC SiPM MicroFC-60035

The electronics include: Audio USB ADC for Theremino MCA, 30V bias voltage for SiPM and basic temperature correction circuit.

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