Timing in silicon detectors for a Compton PET camera

In the scope of construction of a PET apparatus based on detection of Compton scattering in silicon (Compton camera), the timing properties of silicon pad detectors and single and double-sided microstrip detectors are studied. Timing in pad detectors is also studied for 140.5 keV /sup 99m/Tc and 364.5 keV /sup 131/I gamma rays in view of a SPECT application. Compton scattering and energy loss of the Compton electron in silicon detector are simulated using the GEANT package. The electric field in the detector is calculated numerically for a fully depleted detector in the abrupt junction approximation, taking into account the geometry and varying the reverse voltage. Signal formation is studied using Ramo´s theorem and pulse shaping properties of the trigger circuit. The time-walk cut is seen to be directly corresponding to a deposited-energy cut. At a 10 keV threshold in 1 mm thick detectors, 10 ns timing windows are shown to cut a significant portion of events, degrading efficiency or limiting the angular range in a prohibitive way.