MPPC based scintillation counters for the internal photon tagger

We developed scintillation counters with Multi-Pixel-Photon-Counters (MPPC's) for an electron detector of a photon tagging system. They were compact, tolerant to a magnetic field, rate tolerant up to 170 kHz and had a good time resolution. These properties were suitable for the electron detector which was placed in a limited space of a bending magnet of an electron synchrotron. The scintillation counters were used for the measurement of the timing of the passage of the post-bremsstrahlung electrons, and the definition of their orbits by the hit positions on the counters to measure their momenta. We prepared two kinds of scintillation counter, one is for finer granularity named as a TagF and the other for the timing measurement named as a TagB. We performed an experiment to measure the properties of the counter unit using an electron beam with the energy of 855 MeV. We obtained the timing resolution of the TagB to be less than 80 ps (σ) almost independent of the hit rate in the range of 25 kHz to 170 kHz. Its gain decrease at the rate of 170 kHz was ∼ 5% of the gain at the rate of 25 kHz. These properties satisfied our requirements for the electron detector. The whole electron detector consisting of the counter units are currently being designed.