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Title: Self-calibration Method for Dead Time Losses in Neutron Counting Systems

ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1];  [1];  [2]
  1. Los Alamos National Laboratory
  2. KAERI, Republic of Korea
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA), Office of Defense Nuclear Nonproliferation (NA-20)
OSTI Identifier:
Report Number(s):
DOE Contract Number:
Resource Type:
Resource Relation:
Conference: 39th ESARDA conference ; 2017-05-15 - 2017-05-18 ; Dusseldorf, Germany
Country of Publication:
United States

Citation Formats

Ianakiev, Kiril Dimitrov, Iliev, Metodi, Swinhoe, Martyn Thomas, LaFleur, Adrienne Marie, and Lee, Chaehun. Self-calibration Method for Dead Time Losses in Neutron Counting Systems. United States: N. p., 2017. Web.
Ianakiev, Kiril Dimitrov, Iliev, Metodi, Swinhoe, Martyn Thomas, LaFleur, Adrienne Marie, & Lee, Chaehun. Self-calibration Method for Dead Time Losses in Neutron Counting Systems. United States.
Ianakiev, Kiril Dimitrov, Iliev, Metodi, Swinhoe, Martyn Thomas, LaFleur, Adrienne Marie, and Lee, Chaehun. 2017. "Self-calibration Method for Dead Time Losses in Neutron Counting Systems". United States. doi:.
title = {Self-calibration Method for Dead Time Losses in Neutron Counting Systems},
author = {Ianakiev, Kiril Dimitrov and Iliev, Metodi and Swinhoe, Martyn Thomas and LaFleur, Adrienne Marie and Lee, Chaehun},
abstractNote = {},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2017,
month =

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  • Passive Neutron Multiplicity Counting (PNMC) based on Multiplicity Shift Register (MSR) electronics (a form of time correlation analysis) is a widely used non-destructive assay technique for quantifying spontaneously fissile materials such as Pu. At high event rates, dead-time losses perturb the count rates with the Singles, Doubles and Triples being increasingly affected. Without correction these perturbations are a major source of inaccuracy in the measured count rates and assay values derived from them. This paper presents the simulation of dead-time losses and investigates the effect of applying different dead-time models on the observed MSR data. Monte Carlo methods have beenmore » used to simulate neutron pulse trains for a variety of source intensities and with ideal detection geometry, providing an event by event record of the time distribution of neutron captures within the detection system. The action of the MSR electronics was modelled in software to analyse these pulse trains. Stored pulse trains were perturbed in software to apply the effects of dead-time according to the chosen physical process; for example, the ideal paralysable (extending) and non-paralysable models with an arbitrary dead-time parameter. Results of the simulations demonstrate the change in the observed MSR data when the system dead-time parameter is varied. In addition, the paralysable and non-paralysable models of deadtime are compared. These results form part of a larger study to evaluate existing dead-time corrections and to extend their application to correlated sources. (authors)« less
  • The Feynman-Y statistic is a type of autocorrelation analysis. It is defined as the excess variance-to-mean ratio, Y = VMR - 1, of the number count distribution formed by sampling a pulse train using a series of non-overlapping gates. It is a measure of the degree of correlation present on the pulse train with Y = 0 for Poisson data. In the context of neutron coincidence counting we show that the same information can be obtained from the accidentals histogram acquired using the multiplicity shift-register method, which is currently the common autocorrelation technique applied in nuclear safeguards. In the casemore » of multiplicity shift register analysis however, overlapping gates, either triggered by the incoming pulse stream or by a periodic clock, are used. The overlap introduces additional covariance but does not alter the expectation values. In this paper we discuss, for a particular data set, the relative merit of the Feynman and shift-register methods in terms of both precision and dead time correction. Traditionally the Feynman approach is applied with a relatively long gate width compared to the dieaway time. The main reason for this is so that the gate utilization factor can be taken as unity rather than being treated as a system parameter to be determined at characterization/calibration. But because the random trigger interval gate utilization factor is slow to saturate this procedure requires a gate width many times the effective 1/e dieaway time. In the traditional approach this limits the number of gates that can be fitted into a given assay duration. We empirically show that much shorter gates, similar in width to those used in traditional shift register analysis can be used. Because the way in which the correlated information present on the pulse train is extracted is different for the moments based method of Feynman and the various shift register based approaches, the dead time losses are manifested differently for these two approaches. The resulting estimates for the dead time corrected first and second order reduced factorial moments should be independent of the method however and this allows the respective dead time formalism to be checked. We discuss how to make dead time corrections in both the shift register and the Feynman approaches.« less
  • Passive Neutron Coincidence Counting (PNCC) and Passive Neutron Multiplicity Counting (PNMC) based on (Multiplicity) Shift Register (M)(SR) pulse train correlation analyzers is a long established and important non destructive assay method used in the quantification of plutonium and other spontaneously fissile materials across the fuel cycle. Very high efficiency neutron chambers (>60%) are now available and are being applied to ever more demanding items including impure materials with a high ({alpha}, n) rate and articles with a high self-leakage multiplication. This trend means that high instantaneous count rates are commonly encountered such that the multiplicity histogram extends to high order;more » in other words the number of events detected in a single coincidence gate can be large. This poses a problem in that the likelihood of accidental (chance) coincidences due to random events and overlapping (super) fission histories increases and precision is lost in correcting for them. The epithermal design is one attempt to reduce the capture time distribution to minimize the accidentals coincidence rate but the field of application is so broad that high instantaneous rates are still encountered. This inevitably results in the need to apply a correction to the observed Singles, Doubles and Triples rate for dead time losses. When the instantaneous counting rate is high the uncertainties in the applied corrections can be the accuracy limiting factor in the derived counting rate. Controlling and compensating for dead time losses so that target accuracy is achieved is a crucial aspect of a successful design and implementation process. Dead time losses can be reduced substantially on new systems intended for special use by using dedicated preamplifier-discriminators for each {sup 3}He-filled proportional counter together with de-randomiser circuitry and fast encoding electronics. These adaptations are costly, however, and may be difficult to retrofit to existing systems. In this work we therefore take a fresh look at the way in which corrections for dead time losses are applied to the recorded MSR data. We note several interesting empirical correlations observed in experimental data which allow dead time parameters to be extracted. We also comment on the self consistency constraints which exist and can be exploited between PNCC and PNMC results and also between expressions for the correlated rates derived from the random triggered and signal triggered histograms respectively. (authors)« less