Neutron Spectrum Unfolding

Research Focus Areas: 2, 3, & 7

Collaborators: A. Hero & F. Becchetti (Univ. of Michigan), Y. Altmann (Heriot-Watt Univ. U.K.) M. Febbraro (ORNL)

Special nuclear materials (SNM) emit a characteristic neutron fission spectrum. Neutron spectra provide useful information for non-proliferation and treaty verification applications. Organic scintillators are able to detect both neutrons and gamma-rays, and to discriminate between them, thanks to their excellent pulse-shape discrimination capability. The scintillating pulse also retains energy information of the interacting particle. Organic scintillators can thus be used for neutron spectrometry. Neutron energy spectra can be derived by unfolding the neutron detector readout from its light output response function, which can be either measured or simulated from generative models. However, neutron spectrometry via unfolding is a challenging task because requires the solution of an inverse problem.

Our research effort has two main objectives:

  1. Seek better mathematical techniques for solving the unfolding problem and inverting the detector response function, which is an ill-conditioned matrix (in collaboration with Prof. Al Hero – University of Michigan – and Dr. Yoann Altmann – Heriot-Watt University, Edinburgh, UK);
  2. Improve the condition of the matrix using deuterated organic scintillators (in collaboration with Prof. Frederick Becchetti and his group – University of Michigan – and Dr. Michael Febbraro – Oak Ridge National Laboratory).The figure shows the spectrum of a D-D neutron beam measured using an EJ301D deuterated detector (both light output response and neutron spectrum are showed).
Graph of count rate to light output and neutron energy

Related Journal Articles:

  1. A. Di Fulvio et al. “Characterization of Deuterated-xylene Scintillator as a Neutron Spectrometer”
  2. F. Becchetti et al. “Deuterated-xylene (xylene-d10; EJ301D): A new, improved deuterated liquid scintillator for neutron energy measurements without time-of-flight”
  3. S.A. Pozzi et al. “Fast neutron spectrum unfolding for nuclear nonproliferation and safeguards applications”