For nuclear weapon detonations in urban environments, determining the type of weapon and its yield are challenging problems.
A combination of a simple detector design and detailed computer modeling is used to select the best matching source spectrum and compute its yield. Each detector holds various wires consisting of pure materials, that become activated when exposed to neutrons from the weapon.
The method does not try to reconstruct the weapon output spectra – a mathematically ill-posed problem. The AFIDS method compares the measured activation to the activation predicted for every output spectrum in the library.