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HK: Fachverband Hadronen und Kerne

HK 84: Accelerators and Instrumentation I

HK 84.1: Talk

Friday, March 20, 2009, 11:00–11:15, H-ZO 80

Diamonds as fast timing detectors for MIPS: The HADES proton-beam monitor/start detector — •Wolfgang Koenig and Jerzy Pietraszko — GSI, Darmstadt, Germany

Position sensitive mono-crystalline diamond detectors were used successfully as start/beam-monitoring detectors for proton beams (1.2 GeV - 3.5 GeV) at rates of up to 3·10⁶/s/10mm². Two different detector sizes of 3.5×3.5 mm² (4 segments) and 4.7×4.7 mm² (8 segments) were used with thicknesses of 300 µm and 500 µm, respectively. Utilizing dedicated fast amplifiers directly attached to the diamond segments, a time resolution of about 100ps could be achieved with a signal base width of about 8-10 ns and ≥95% detection efficiency. The signal/RMS-noise ratio amounted to 22 (300 µm) and 26 (500 µm) at rise times of 1.2 ns and 1.3 ns, respectively. The measured time resolution is about a factor of two worse than expected from the signal/noise ratio. A significant variation of rise times was observed which most likely results from rather inhomogeneous intrinsic fields (upcharging effects due to charge trapping). Furthermore, at high rates unreasonably large leakage currents appeared for some detectors which eventually resulted in sudden discharges, tripping the detector bias. These effects seem to depend strongly on the metallization procedure. An optimization of this procedure is currently investigated.