Passive neutron detectors, including activation foils, use neutron absorption reactions with known cross-sections to determine a level of neutron radiation received over time. These reactions, and subsequently activation foils, are chosen because of their reaction cross-sections at various neutron energy levels and the resulting activation products.
Different activation foil nuclides have strongly varying neutron cross-sections at different energy levels. By selecting an appropriate set of foils, the energy dependence of the neutron field can be characterized and information about the spectrum and the magnitude of the fluence can be obtained. For the Activation Foil Integrated Detector System (AFIDS), a specific setup is used to distinguish between nuclear weapons detonation leakage spectra.
The selection of various elements for use in foils and their dimensions for AFIDS was initially based on informed judgement, but no rigorous optimization has been done. Since this system could be deployed in cities nationwide, cost is a key consideration alongside the ability to distinguish different spectra.
This research will provide a method to optimize both the AFIDS detectors, based on ability to differentiate between expected leakage spectra and the cost while maintaining feasibility and reliability. This method will lead to a code which will be generalized for other activation foil applications and spectra.