On the Possibility of Correlation Measurements with Fission Chambers and Campbell Techniques

Year
2014
Author(s)
L ´ena ´rd Pa ´l - Hungarian Academy of Sciences
Imre Pa ´zsit - Chalmers University of Technology
Abstract
The signals of fission chambers, a type of ionization chambers, are usually evaluated with the help of the co-called Campbelling techniques, the essence of which is that in the current mode, relationships exist between the various order moments of the signal. This gives the possibility to determine the mean value of the intensity of the detection events from the higher moments of the detector current. However, the Campbell theorems used are only valid if the incoming primary events constitute a Poisson process. The objective of this work is the extension of the Campbell technique for the case when the incoming particle events are not independent, rather correlations exist between them due to the fact that the particles are generated in the branching process of neutron multiplication in a multiplying medium. Recently, a formalism was elaborated to derive the traditional Campbell techniques for independent initial events in a transparent way by using the integral form of the backward master equations [4]. In the present work this formalism is extended to incorporate the particle multipli- cation in the medium prior to the detection events. The multiplication in the subcritical medium is driven by a source with Poisson statistics. The arising modified Campbell formulae contain the effect of the particle multiplication, thus they account for the fact that the detection events are not independent. The methodology and the derivation of the modified Campbell relationships is given, and the potential application of the method for characterizing special nuclear materials are discussed.