Estimation of 240 Pu effective mass of fuel plates based on a singles and coincidence acquisition mode with organic scintillators

The time distributions of neutron and gamma events for the plutonium metal plates of different isotopic compositions in a singles and coincidence acquisition mode were measured with the Fast Neutron Multiplicity Counter (FNMC) consisting of 8 EJ-309 liquid scintillators and 8 stilbene detectors. Since time intervals between detected events depend on the source activity, estimation of 240 Pu effective mass in an investigated sample was based on the calibration curve obtained by using a subset of the remaining Pu metal plates. It was demonstrated that the neutron time interval distributions can provide the evaluation of 240 Pu effective mass with high accuracy. The Kolmogorov complexity (KC) and Lyapunov exponent were calculated to reveal the presence of a chaotic and non-random time series in all the measured ones.