CdTe and CdZnTe detectors for timing measurements

We measured timing properties of CdTe and CdZnTe semiconductor detectors with planar configuration. We developed a new method to evaluate their performance in timing resolution utilizing an ²⁴¹Am-doped plastic scintillator. We confirmed that the low mobility and short lifetime of holes are major obstacles to their timing resolution. However, their timing properties can be very much improved, either by applying a high electric field that increases the carrier speed or by selecting those events which are dominated by the electron signal. We demonstrated the latter through a pulse-shape discrimination technique using two different integration time constants. In conjunction with a newly developed CdTe diode, we obtained a superior timing resolution of 5.8 ns. We also discussed the application of CdTe to positron emission tomography (PET), employing the standard 511 keV gamma-gamma coincidence method. We confirmed that a geometrical configuration in which the electrodes are parallel to the incident γ-rays gives about three times better timing response than a geometry when the electrodes are perpendicular to the γ-ray beam.