Comments on the stochastic characteristics of fission chamber signals

Rapport, 2013

This report presents a theoretical investigation of the stochastic properties of the signal series of ionisation chambers, in particular fission chambers. The signals of the detector are assumed to be generated by incoming particles correspondig to an inhomogeneous Poisson distribution. Each incoming particle generates a current pulse with constant shape and random amplitude, and the detector signal consists of the time series of such current signal pulses incurring also a pile-up effect in the case of high intensity of the primary events. Exact relationships are derived for the higher order moments of the detector signal, which constitute a generalisation of the so-called higher order Campbelling techniques. The probability distribution of the number of time points when the signal exceeds a certain level is also derived. Assuming that the incoming particles form a homogeneous Poisson process, explicit expressions are given for the higher order moments of the signal and the number of level crossings in a given time interval for a few selected pulse shapes.