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Study of a possible silicon photomultiplier based readout of the large plastic scintillator neutron detector NeuLAND

Hensel, T.; Weinberger, D.; Bemmerer, D.; Boretzky, K.; Gasparic, I.; Stach, D.; Wagner, A.; Zuber, K.

The NeuLAND (New Large-Area Neutron Detector) plastic scintillator based time of flight detector for 0.2-1.6 GeV neutrons is currently under construction at the Facility for Antiproton and Ion Research (FAIR), Darmstadt, Germany. In its final configuration, NeuLAND will consist of 3,000 2.7 m long plastic scintillator bars that are read out on each end by fast timing photomultipliers.

Here, data from a comprehensive study of an alternative light readout scheme using silicon photomultipliers (SiPM) are reported. For this purpose, a typical NeuLAND bar was instrumented on each end with a prototype of the same geometry as a 1'' photomultiplier tube, including four 6x6 mm^2 SiPMs, amplifiers, high voltage supply, and microcontroller.

Tests were carried out using the 35 MeV electron beam from the ELBE superconducting linac with its ps-level time jitter in two different modes of operation, namely parasitic mode with one electron per bunch and single-user mode with 1-60 electrons per bunch, using Acqiris fast digitizers. In addition, offline tests using cosmic rays and the NeuLAND data acquisition scheme were carried out.

Typical time resolutions of sigma <= 100 ps were found for $\geq$99\% efficiency, improving on previous work at ELBE and exceeding the NeuLAND timing goal of sigma < 150 ps. Over a range of 10-300 MeV deposited energy in the NeuLAND bar, the gain was found to deviate by <=10% <=20% from linearity for 35 um (50 um) SiPM pitch, respectively, satisfactory for calorimetric use of the full NeuLAND detector. The dark rate of the prototype studied was found to be 70-200 s^-1, comparable with the unavoidable cosmic-ray induced background.

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Publ.-Id: 34940