Undergraduate Research at Jefferson Lab

Silicon Photomultiplier Characterization After High Gamma Radiation

Student: Brad T. Damiano

School: Christopher Newport University

Mentored By: Carl Zorn

The SiPM is a limited Geiger-mode avalanche photodiode (GAPD) which allows it to detect very low light intensities with 20-50% photon detection efficiency (PDE) with an amplication of the signal similar to that of a standard PMT. In contrast to PMTs, SiPMs are immune to magnetic fields allowing them to operate at 1 T within the GlueX calorimeter detector as a complete replacement for PMTs. Hamamatsu Corporation has sent 25 SiPMs to be characterized in terms of standard parameters such as darkrate and PDE after irradiation by a high energy gamma source. This study shows that although the PDE remains relatively stable between pre-irradiation, immediate post-radiation, and post-annealing, the noise level (measured as dark rate) after the irradiation is significantly higher. It was observed that the 15µ SiPMs displayed a larger variance in the post-irradiation changes among the samples. Some SiPMs responded very poorly and had an extreme increase in dark noise, while others responded well and had approximately the same level of relative dark noise increase as the 50µ samples. Collected data will assist Hamamatsu in their efforts to improve the radiation tolerance of SiPMs. The relatively low radiation tolerance of SiPMs is one the major defects to overcome before they can be adopted at a larger scale.