Complexity measures and occurrence of the breaking point in the neutron and gamma-rays time series measured with organic scintillators

TL;DR

This study applies complexity measures, including Kolmogorov complexity and Lyapunov exponents, to neutron and gamma-ray time series from plutonium samples, revealing correlations between complexity values and sample characteristics.

Contribution

It introduces the use of information-theoretic complexity measures to analyze nuclear material detection signals, linking complexity drops to the breaking point in neutron and gamma-ray time series.

Findings

High similarity in complexity for samples with 5-15 plates

Lower complexity observed in samples with 3 plates

Complexity measures can indicate measurement uncertainties

Abstract

This paper deals with the first analysis of the neutron and gamma time series measured with organic scintillators from plutonium samples by using information measures. Fast neutron detection with organic scintillators has been widely used for various nuclear applications and homeland security. One of the significant attributes of special nuclear materials (SNM) is the high multiplicity events in a short period of time. The time distributions of neutron and gamma-rays events for the plutonium metal plates designed as fuel plates for the Idaho National Laboratory (INL) Zero Power were measured with the Fast Neutron Multiplicity Counter (FNMC) consisting of 8 EJ-309 liquid scintillators and 8 stilbene detectors. Since the neutron correlated counts within the coincidence window of 40 ns are related to 240Pu effective mass of plutonium metal plates we investigated the randomness of the measured neutron and gamma-rays events. To access such information, we resort to complexity measures in the hope of being able to connect complexity values with the reliability of detection. That was done through (i) application of Kolmogorov complexity (KC) and its derivatives [Kolmogorov spectrum and its highest value (KCM) and running complexity (RKC)] and (ii) establishing the breaking point after which there exists a sharp drop in the running Kolmogorov complexity of the neutron and gamma-rays time series. It was found that the complexity of all the time series detected from the sample with 5, 9, 11, 13, and 15 plutonium plates had the high almost identical values of KC while the sample with 3 plates had by one-third smaller KC values than all the others. These calculations were supplemented by the Lypaunov exponents for a time series and the NIST tests. The low KC values can be addressed to the different sources of uncertainties in measuring procedure with the sample consisting of three plates.