Speaker
Description
The time distribution and energy spectra of the delayed neutrons emitted from fission
provide information about the excitation energies of the fission fragments and reveal structure properties of the fragments. In addition, detection of delayed neutrons and γ-rays provide clean signatures for identifying fissile materials in γ-ray beam-based cargo scanners. Accurate prompt and delayed particle emission data for photon-induced fission are essential for developing technologies for assaying nuclear devices based on remote interrogation techniques using γ-ray beams. Optimum use of the probe γ-ray beam involves detection and analysis of the energy spectra of the γ-rays and neutrons emitted from γ-ray induced nuclear reactions on the container and its contents. This work focuses on the delayed neutrons from photofission of actinide nuclei. We are measuring the first double differential (time and energy) distributions of the delayed neutrons emitted in photon-induced fission using a mono-energetic γ-ray beam. These measurements are performed at the High Intensity Gamma-ray Source (HIγS) at TUNL using a circularly polarized beam in the energy range of 6 to 10 MeV. The energy spectra of the delayed neutrons are measured using $^3$He ionization detectors. This presentation will describe the GEANT-4 modeling of the neutron detection in
the $^3$He ionization chambers.
- This research is supported in part by the U.S. Department of Homeland Security (DHS), Countering Weapons of Mass Destruction (CWMD) Academic Research Initiative (ARI) under grant no. 20CWDARI00035-01-00 and by the U.S. Department of Energy under grant nos. DE-FG02-97ER41033 and DE-SC0005367.