Effects of radiation damage caused by proton irradiation on Multi-Pixel Photon Counters (MPPCs)

TL;DR

This study examines how proton irradiation causes radiation damage in Multi-Pixel Photon Counters, affecting their leakage current, photon-counting ability, and pulse-height resolution, with implications for their use in radiation environments.

Contribution

It provides detailed measurements of radiation effects on MPPCs, including leakage current increase and loss of photon-counting capability at specific doses, which was not previously characterized.

Findings

Leakage current increases linearly with dose

Photon-counting capability is lost after 21 Gy irradiation

Pulse-height resolution slightly deteriorates after 42 Gy

Abstract

We have investigated the effects caused by proton-induced radiation damage on Multi-Pixel Photon Counter (MPPC), a pixelized photon detector developed by Hamamatsu Photonics. The leakage current of irradiated MPPC samples linearly increases with total irradiated doses due to radiation damage, which is not completely recovered even after a year from the irradiation. No significant change has been observed in the gains at least up to 8.0 Gy ($9.1\times10^7$ n/mm$^2$ in 1 MeV neutron equivalent fluence, $\Phi_{\rm eq}$). The device has completely lost its photon-counting capability due to baseline fluctuations and noise pile-up after 21 Gy irradiation ($2.4\times10^8$ n/mm$^2$ in $\Phi_{\rm eq}$), which might be problematic for some applications, such as ring-imaging Cherenkov detectors. We have found that the pulse-height resolution has been slightly deteriorated after 42 Gy irradiation ($4.8\times10^8$ n/mm$^2$ in $\Phi_{\rm eq}$), where the measured sample has been illuminated with a few hundred photons. This effect should be considered in the case of energy-measurement applications.