Fission Chain Analysis

Research Focus Areas: 2 & 4

Ph.D. Students: M. Monterial (Graduated)

Collaborators: P. Marleau (SNL)

Fast organic scintillators with pulse shape discrimination capability can measure gamma-rays and neutrons correlated by emission processes such as fission, alpha n reactions, and inelastic scatter. In fissile materials, nanosecond time resolution enables the direct measurement of the temporal distribution of fissions in a fission chain. By correcting for the time-of-flight of fast neutrons by estimating their energy using the amount of scintillation light detected, the inter-fission timing distribution can be directly derived from the measured time between gamma-rays and neutrons.

This Time Of Flight Fixed by Energy Estimation (TOFFEE) distribution contains information regarding the time development of fission chains such as the multiplication of the fissile material and the thickness and average atomic number of surrounding materials (moderators).  We are actively developing novel analysis methodologies to retrieve these physical factors from TOFFEE distributions.

Because these physical factors are derived purely from the inter-event time, this method does not suffer from many of the difficulties found in multiplicity counting based analyses.  Our analysis does not require knowledge of the efficiency of the system, nor are there assumptions made regarding the size of the fissile material or timescale of the development of fission chains as is required in point kinetics models.

If successful, this research may make possible new and better methods for characterizing assemblies of fissile material.

Fast organic scintillators

Related Journal Articles:

  1. M. Monterial, P. Marleau, M. Paff, S. Clarke, S. A. Pozzi, “Multiplication and Presence of Shielding Material from Time-Correlated Pulse-Height Measurements of Subcritical Plutonium Assemblies.” Nuclear Instruments and Methods in Physics Research Section A, Accepted for publication January 18, 2017.
  2. M.G. Paff, M. Monterial, P. Marleau, S. Kiff, A. Nowack, S.D. Clarke, S. A. Pozzi, “Gamma/Neutron Time-Correlation for Special Nuclear Material Detection – Active Simulation of Highly Enriched Uranium.” Annals of Nuclear Energy, October 2014, 72, pp. 358-366.

Related Conference Proceedings:

  1. M. Monterial, P. Marleau, S. A. Pozzi, “Demonstration of Time-Correlated Pulse Height Template-based Confirmation Measurements”, 57th Annual Institute of Nuclear Materials Management Meeting, July 24-26, Atlanta, Georgia.
  2. M. Monterial, P. Marleau, S.A. Pozzi, “Detection and Charectarization of Highly Enriched Uranium Under Active Interrogation Through Time Correlated Fission Events”, 2015 IEEE Nuclear and Science Symposium and Imaging Conference, Oct 31- Nov 1, 2015, San Diego, California.