The effects of fission neutron correlations in Monte Carlo simulations of neutron multiplicity counters

Year
2017
Author(s)
H.O. Menlove - Los Alamos National Laboratory
Andreas Enqvist - University of Florida
R. Weinmann-Smith - University of Florida
Madison T. Andrews - Los Alamos National Laboratory
A.C. Trahan - Los Alamos National Laboratory
M.E. Rising - Los Alamos National Laboratory
Abstract
Monte Carlo simulations are frequently used in safeguards to model neutron multiplicity detectors. The simulations typically sample properties such as the number of fission neutrons and their energies and directions from independent probability density functions. However, multiplicity counters detect event-based neutron correlations and so more accurate modeling is needed. To respond to this need, the Fission Reaction Event Yield Algorithm (FREYA) and the Cascading Gamma-ray Multiplicity with Fission (CGMF) models were added in the newest version of MCNP, MCNP6.2. The models include analog fission physics with n-n, n-y, y-y, and multiplicity correlations conserving momentum, energy, and angular momentum for individual fission events.