Radiation damage studies on SiPMs for calorimetry at the Super LHC

A typical scintillating tile sampling calorimeter consists of multiple layers of scintillators coupled to wavelength shifting fibers viewed by a suitable photo-detector. Long clear fibers are used to connect the tiles to the readout modules. We have investigated the use of silicon photomultipliers (SiPMs) at the Super Lagre Hadron Collider (SLHC). Because radiation hardness is the main concern, two sets of radiation data were taken using a 212 MeV proton beam at Massachusetts General Hospital. In the first data set we radiated up to a dose of 3×10¹⁰ protons per cm² using diodes from three different manufactures (i.e., FBK, CPTA and Hamamatsu). At a dose of 3x10¹⁰ protons per cm² only small effects of PDE loss were detected due to very high dark count always occupying one or more cells in a multi-cell SiPM. A second set of data up to 10¹³ protons per cm² using very high pixel density MAPDs with up to 40,000 cells per mm². After each small radiation dose multiple scope traces were taken to look at the PDE and dark count of the devices. The increase in dark count due to the radiation was compared to the DC leakage current. Also a comparison was made between multi-cell and single-cell samples of the FBK-IRST diodes.