Method and apparatus for measurement of time integrals of exponentially decaying pulses

The circuit is adapted for integration of pulse signals of the shape U(t)=U0exp(-t/ tau ), wherein the time constant tau can be determined in advance by a calibration measurement, in particular signals from a scintillation detector. The purpose is to treat pile-up phenomena, without measuring the integration time, wherein the measured integral is corrupted because the time distance between two pulses becomes smaller than the integration time for the first pulse. The circuit comprises an integrator (4, 5, 6, R, C) for the pulse signal and a summator (3, R1-R3) for forming a weighted sum of the pulse signal (on 1, 2) and the integrated signal (from 4, 5), the weight of the pulse signal and the weight of the integrated signal having such a relation to each other that the result signal (on 8) is proportional to the sum of the time integral of the pulse signal and tau times the pulse signal. The circuit implements the equation I INFINITY = +TR The output signal is generated in a time significantly shorter than the time constant tau and is independent of time, except for the risetime necessary. Accordingly the measurement can be interrupted anytime, for example at the detection of pile-up, without necessitating a succeeding conversion calculation on the basis of the actual integration time.