Abstract
In two earlier papers [1], [2] we investigated the possibility of extracting traditional multiplicity count rates from the cumulants of fission chamber signals in current mode. It was shown that if all neutrons emitted from the sample simultaneously are also detected simultaneously, the multiplicity rates can be retrieved from the first three cumulants of the currents of up to three detectors, but the method breaks down if the detections of neutrons of common origin take place with a time delay spread wider than the pulse shape. To remedy these shortcomings, in this work we extended the theory to two- and three-point distributions (correlations). It was found thatthe integrals of suitably chosen two- and three-point moments with respect to the time differences become independent of the probability density of the time delays of detections. With this procedure, the multiplicity rates can be retrieved from the detector currents for arbitrary time delay distributions. To demonstrate the practical applicability of the proposed method, a measurement setup was designed and built. The statistics (shape and amplitude distribution) of the detector pulse were investigated as important parameters of the theoretical model. Simulations were performed to estimate the expected value of the multiplicity rates in the built setup. Measurements were performed and two types of moments (the mean and the covariance function) of the recorded detector signals were calculated. Values of singles rates were successfully recovered.
Highlights
The primary objective of multiplicity counting is to determinethemassofsmallfissilesampleswhichisextractedfrom the detection rates of single, double and triple coincidences (S, D and T count rates) with pulse counting techniques [3]
The results showed that when the width of the density function of the time delay is much wider than the pulse width, the coefficients of the D and T rates will become vanishingly small, only the S rates can be unfolded from the cumulants
A new form of neutron multiplicity counting has been developed with the possibility of extracting traditional multiplicity count rates from the cumulants of fission chamber signals in current mode
Summary
The primary objective of multiplicity counting is to determinethemassofsmallfissilesampleswhichisextractedfrom the detection rates of single, double and triple coincidences (S, D and T count rates) with pulse counting techniques [3]. The results showed that when the width of the density function of the time delay is much wider than the pulse width (which is a typical case is thermal detection systems), the coefficients of the D and T rates (analogues of the doubles and tripes gate factors in pulse counting methods) will become vanishingly small, only the S rates can be unfolded from the cumulants At the end of the paper, some preliminary experimental results will be presented as well
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