The report is devoted to the study of radiation resistance of silicon photomultipliers (SiPM) produced by HAMAMATSU. SiPM was irradiated in neutron fluxes of the JINR IBR-2 reactor. The tested SiPM received fluence from 1012 up to 2x1014 of neutrons/cm2. Irradiated detectors were investigated using a radioactive source and laser flashes at a temperature of -30oC. The measurements showed that the SiPM remain fully functional as photon detectors up to neutron fluence 2x1014 despite a significant increase in noise.
A future replacement of the HE calorimeter for scintillator section of the CMS HL-LHC
endcap calorimeters during the LS3 period presupposes the installation of the photo detectors (SiPM)
directly on the scintillation tiles [
Silicon photomultipliers (SiPM) are a new type of photodetectors. They consist of miniature diodes operating in streamer mode (APD). The detector has a high sensitivity and is able to register individual photons On the one hand, SiPM is characterized by a low supply voltage and insensitivity to the magnetic field, and on the other, by a high dependence of the gain on temperature and the destruction of the detector structure in the strong radiation fields typical for modern spectrometers.
The work is devoted to the study of radiation effects on SiPM structures.
JINR group performs the investigation of some SiPM properties after irradiating them with neutrons at the IBR-2 reactor. The main goal of the work is to estimate the upper limit of neutron irradiation, which will lead to the impossibility of further use of SiPM in the central region of the scintillation part of CMS calorimeters cooled to -30 °C. The main criterion for the operation of SiPM is the possibility of recording by a photo detector MIP signals above the noise level.
Irradiation of 21 SiPM photo detectors with fast neutrons was carried out in two runs at IBR-2
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MPPC S12571-010C MPPC S12571-015C MPPC S13360-1325CS
Three photo detectors, one of each type, were combined in a set. There were seven sets in tota. SiPMs of each set received the same neutron radiation. The sets were irradiated in the range of fluence values 1.7 × 1012 ÷ 2.1 × 1014 neutrons/cm2. Table 2 shows the magnitudes of neutron fluence and the date of irradiation for each set of photo detectors. The magnitude of neutron fluence was measured by two methods: The first method was standard and used at IBR-2. The technique was based on measuring the induced activity of Nickel wires irradiated together with the samples. The second method was based on the measurement of the quantity of defects in two silicon semiconductor detectors located near each set of SiPM devices.
All photodetectors passed test procedures to measure the main parameters after irradiation and to compare them with parameters defined in factory specifications. Table 3 presents the main parameters of the investigated devices.
The parameters of unirradiated SiPMs were taken from the Hamamatsu data sheets. All the values were specified for + 25 °C. For S12571-010C and S12571-015C amplification (M), operating voltage (Vop) and dark noise frequency (Fdark) at the threshold of 0.5 pixels are given. The breakdown voltage (Vbr) was not specified. The data sheet of S13360-1325SS specified the typical dark current as 70 kHz and the typical gain as 7.0×105. There was indicated the breakdown voltage (Vbr) and current of the detector (Id) for each device in the present paper.
All SiPM photo detectors were examined before and after irradiation. For the measurement we used a setup shown in Figure 1. The signal in the scintillator was excited by two sources: The first one was a 90Sr radioactive source. The second one is a laser whose signal was as from a particle with a minimum ionizing capability (MIP).
The SiPM response was measured at room temperature and at -30 °C.
The results of measurements of SiPMs irradiated to a value of 5.38 × 1012 neutrons/cm2 are shown in Figure 2 for the light signal excited by a radioactive source. The results of laser measurements of the same SiPM devices are shown in Figure 3. For a cooled photo detector the MIP signal is almost 12 times higher than the noise level.
The results of measurements of SiPM devices irradiated to 2.09 × 1014 neutrons/cm2 for both sources of light are shown in Figure 4. A photo detector was cooled up to -32 °C. Measurements at room temperature were not carried out because the noise level from the photo detector was too high.
A registration of the MIP signal for SiPMs irradiated to 2.09 × 1014 neutrons/cm2 becomes problematic due to a high noise level even at -32 °C. The signal-to-noise ratio is at the level of ~ 1. Laser Test
T=+25 OC S/N=1.8 T=-32OC S/N=11.8
Signal ~14p.e.
Noise Signal ~14p.e.
JINR study shows that up to irradiation levels of ~ 5.4 × 1012 neutrons / cm2, the above-mentioned Hamamatsu photodetectors will ensure the recording of signals from MIP particles in case of SiPMon-tile readout in the scintillator section of the CMS HL-LHC endcap calorimeters.