A New Constant Fraction Timing System with Improved Time Derivation Characteristics

A constant fraction timing system having excellent time derivation properties over a wide dynamic range of signals is described. Leading edge walk is significantly reduced by arming the constant fraction zero-crossing circuit with a discriminator that is separate from the energy discriminator. Timing resolution with Ge(Li) detectors can be improved by the optional use of a slow risetime reject circuit, but only at the expense of reduced counting efficiency. This performance trade-off is described in detail. Extensive data are presented on the timing performance in ¿-¿ coincidence experiments.