Embodiments for providing rapid characterization of an unknown nuclear source are described. A sequential Bayesian particle filter is used to analyze in real time the neutron inter-arrival times to estimate the multiplication of the source, the mass of the spontaneously fissioning isotope, the neutron detection efficiency, and the neutron lifetime. A method defines an array of trial solutions, each specifying a combination of fissile parameters characterizing the source; determines a first time interval between a first neutron and a second neutron detected by the neutron detector; calculates a probability distribution of an array of the parameter values; determines additional time intervals between each subsequent successive pairs of neutrons detected by the neutron detector; and refines the probability distribution based on the additional time intervals using a recursive Bayesian process to estimate the most probable combination of parameter values.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
 The United States Government has rights in this invention pursuant to Contract No. DE-AC52-07NA27344 between the United States Department of Energy and Lawrence Livermore National Security, LLC.