  Silicon PhotoMultipliers (SiPM) are an excellent choice for the scintillator
light readout at hadron calorimeters due to their insensitivity to magnetic
fields, low operating voltages, low cost, compactness and mechanical endurance.
They are already successfully utilized in Projectile Spectator Detector (PSD)
of NA61 at CERN, and will be utilized soon in PSD of CBM at FAIR and Forward
Hadron CALorimeters (FHCAL) of BM@N at NICA heavy-ion collision experiments.
The main issue of SiPM application is their degradation due to high neutron
fluence that can reach up to 2E11 neq/cm2 per year of the experiment operation.
Multiple irradiation tests of SiPMs produced by Ketek, Zecotek, Hamamatsu and
Sensl manufacturers were conducted at the cyclotron of NPI Rez with a broad
neutron spectrum and total fluences in the wide range of 5E10 - 6E12 neq/cm2.
Detailed characterisation of all SiPMs was performed based on dependencies of
dark current on voltage, capacitance on voltage and frequency, and response to
LED light on voltage. SiPM's breakdown voltage, quenching resistance, pixel
capacitance, gain and signal to noise ratio were extracted from these
measurements. Those parameters' dependence on neutron fluence and their
variability are discussed. Performance of the PSD calorimeter module equipped
with irradiated SiPMs in CERN during the beam scan with 2 - 80 GeV/c protons is
briefly overviewed.
