Neutron Activation Analysis (NAA) and its variants, Prompt Gamma Neutron Activation Analysis (PGNAA), Portable Isotopic Neutron Spectroscopy (PINS), and Gamma Spectrosopy is a sensitive multi-element analytical technique in which a sample is bombarded with neutrons from a radioactive source, causing the elements in the sample to form radioactive isotopes. The radioactive decay paths of the formed radioisotopes are detected with a gamma radiation detector and compared with reference decay data to determine the atoms present in the interrogated sample. A small sample of Californium-252 is typically used as the neutron source. The advantage of NAA is that it can determine the presence of a variety of substances such as chemical warfare agents, explosives, and hazardous materials inside thick-shelled containers such as munitions shells, barrels, and other metal containers.