Title: Improvements in Dead-time Correction Using List-mode Neutron Counters
Authors: HOLZLEITNER LudwigSWINHOE Martyn T.
Citation: Proceedings of the 33rd ESARDA ANNUAL MEETING p. 1 - 11
Publisher: ESARDA
Publication Year: 2011
JRC N°: JRC62536
URI: http://esarda.jrc.ec.europa.eu/
Type: Articles in periodicals and books
Abstract: Neutron multiplicity counting is a widely used technique in safeguards to determine the mass of fissile material. Unfortunately the multiplicity measurement is disturbed by the dead-time effect, which prevents pulses from being detected by the electronic chain on the same channel when they follow shortly in time after another pulse. This is particularly important since this loss due to dead-time especially affects neutrons originating from multiple-emission events, which in fact carry a lot of information about the sample and so should be measured. There exist a number of different dead-time correction methods. The most widely used (INCC) makes use of a semi-empirical correction for the single and double neutron emissions (Singles, Doubles) and another method (of Dytlewski) for Triples. They require the application of a pre-delay and of dedicated calibration measurements in order to determine the necessary parameters. Other correction methods have had little in-field use because of the complexity of their formulation. In this paper we present a new approach for correction, based rather on mathematical-combinatorial theory than on heuristic formulas suggested by the physical principles. In contrast to other existing methods this correction is applied to the multiplicity distributions of measured “Reals plus Accidentals” and “Accidentals”. Test results for this new method using simulations are presented as well as comparisons to other, well established methods for dead-time correction. This new technique requires the deployment of new, so-called multi-channel list mode counters. This new approach will result in a number of advantages over the heuristic one: since the Singles, Doubles, Triples, etc. are calculated later from the multiplicity distribution, this method will be suitable to correct also for higher number of simultaneous neutron emissions than Triples (Quadruples, Quintuples). Since this method is based on the collected data itself, no prior calibration will be necessary. Furthermore use of a pre-delay may not be necessary, leading to an increased gate-fraction and – in principle – to increased quality of the results. Although this method is still under development, it has already demonstrated good results for low and medium count-rates.
JRC Directorate:Nuclear Safety and Security

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