Fissile material detection using neutron time-correlations from photofission

Abstract

The detection of special nuclear materials (SNM) in commercial cargoes is a major objective in the field of nuclear security. In this work we investigate the use of two-neutron time-correlations from photo-fission using the Prompt Neutrons from Photofission (PNPF) detectors in Passport Systems Inc.'s (PSI) Shielded Nuclear Alarm Resolution (SNAR) platform for the purpose of detecting ∼5 kg quantities of fissionable materials in seconds. The goal of this effort was to extend the secondary scan mode of this system to differentiate fissile materials, such as highly enriched uranium, from fissionable materials, such as low enriched and depleted uranium (LEU and DU). Experiments were performed using a variety of material samples, and data were analyzed using the variance-over-mean technique referred to as Y2F or Feynman-α. Results were compared to computational models to improve our ability to predict system performance for distinguishing fissile materials. Simulations were then combined with empirical formulas to generate receiver operating characteristics (ROC) curves for a variety of shielding scenarios. We show that a 10 second screening with a 200 µA 9 MeV X-ray beam is sufficient to differentiate kilogram quantities of HEU from DU in various shielding scenarios in a standard cargo container. * soltz1@llnl.gov

On the Feynman-alpha Method for Reflected Fissile Assemblies

“…The assemblies were measured with an organic scintillator array (OSCAR [12]). Previous works have also used organic scintillators to perform Feynman-alpha measurements [30,31,32], although 3 He detectors are traditionally used. The OSCAR comprised 12, cylindrical, 5.08-cm thick × 5.08-cm diameter trans-stilbene organic scintillators (C 14 H 12 ) wrapped in polytetrafluoroethylene tape and housed in aluminum [33,34], coupled to photomultiplier tubes (PMTs), and arranged in a 3×4 matrix.…”

Parameterization of prompt neutron multiplicity for first-chance actinide photofission

“…The experimental data and evaluation of prompt neutron yield in the case of actinides photofission are practically absent at the present time [2][3][4]. Data about the yields of prompt neutrons is necessary to solve the current problems of atomic engineering, such as the methods of nuclear fuel burning and long-lived actinide decontamination, detecting and studying the characteristics of special nuclear materials, and others [5][6][7]. Especially this is true for photonuclear data [8,9].…”