Speaker
Description
Silicon photomultipliers (SiPMs) are candidate photodetectors for the LHCb RICH upgrade II, where they are required to operate reliably in high radiation environments. Critical parameters such as dark count rate, gain stability, and photon detection efficiency were therefore evaluated as a function of neutron fluence. The results indicate a significant increase of DCR, noise and leakage current, while maintaining acceptable signal response with optimized biasing and cooling. These findings suggest that, despite radiation-induced degradation, SiPMs remain viable candidates for LHCb detector systems with proper mitigation strategies.This work overviews results from irradiated samples exposed up to 2x10^13 1 MeV neutron eq/cm².
Summary (500 words)
In the planned LHCb Ring Imaging Cherenkov Detector (RICH) upgrade II, silicon photomultipliers (SiPMs) are considered one of the most promising photodetector candidates. In the LHCb RICH detector environment the photosensitive surfaces are expected to be irradiated with up to 2 10^13 1 MeV neutron eq/cm², 12kGy TID and 10^13 HEH (>20 MeV)/cm2 [1]. In these conditions the selected detector is expected to retain the single photon timing resolution (SPTR), below 100 ps Full Witdh Half Max (FWHM), and being able to operate within a gate of 25 ns (40 ns bunch crossing). While SiPMs are the preferred candidates for the upgrade, their vulnerability under harsh conditions remains a serious concern. The upgrade of the RICH detector that will be required to cope with 1.5 x 1034 cm-2s-1 maximum luminosity, foresees the coverage of 1.5 m2 with pixel detector with of 1.4 mm pitch, and additional 2 m2 with a 2.4 mm pitch. Considering that radiation damage will deteriorate the Dark Count Rate (DCR) from 100 kHz/cm2 toward an estimated rate around MHz/cm2, the operation of the detector will become a challenge. To assess detector performance after high irradiation burden, we irradiated SiPM samples at the Triga nuclear reactor in Ljubljana [2]. We systematically characterized DCR, leakage current, brake down voltage and SPTR using a setup which allows us to thermally stabilize the samples down to liquid nitrogen conditions (-180 C) (figure 1).
In this work we present and compare the results obtained from multiple irradiation campaigns and from different projects. Initially 5 SiPMs from Fondazione Bruno Kessler were characterized and evaluated, thereafter irradiated with different doses and re-analyzed [3]. Temperatures of stable operation at different fluences are shown on the left side of Figure 2. In another project, called spadRICH, several SPADs based on 55 nm [4] and 110 nm [5] CMOS technology were irradiated along with micro lenses. The micro lenses are beneficial to recover the geometrical acceptance [6] and don’t show signs of optical deterioration under neutron radiation exposure. DCR for various SPADS in 55 and 110nm as a function of temperature are shown of the right side of Figure 2 [7].