Unexploded ordnance discrimination using neutrons

Abstract

In the U.S., the majority of unexploded ordnance (UXO) is often found to pose no risk, since inert and explosive ordinance can easily be distinguished. However, there are items that are not identifiable due to age and condition. These UXO must often be treated as though they contained high explosives or other hazardous material. This leads to unnecessary cost and potential impacts to the environment and communities. For subsurface anomalies, excavation is necessary for visual inspection. This procedure adds to the risk and cost associated with neutralizing UXO. Pulsed fast/thermal neutron analysis (PFTNA) is a technique used for bulk chemical analysis. In PFTNA, neutrons are produced with a pulsed 14 MeV (d-T) neutron generator. Separate gamma-ray spectra from fast neutron, thermal neutron and activation reactions are accumulated and analyzed to determine elemental content. A man-portable explosives detection system called PELAN has been developed using this technique. Recent tests of the PELAN have shown that this system works very well for artillery shells larger than 90 mm with false negative rates less than 1%. For smaller munitions, the false negative increases dramatically to values greater than 50%. This increase is due to the poor signal to noise ratio present when PELAN is used to examine smaller UXO.