  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.
