As the ability to detect subsurface metallic objects increases, organizations that must remediate sites designated for base realignment and closure (BRAC) and Formerly Used Defense Sites (FUDS) face an increasing problem in the differentiation of unexploded ordnance (UXO) from other metallic clutter. The problem is further exacerbated at former ranges where ordnance filled with inert materials was fired during testing and training. Currently, it is necessary to treat every piece of ordnance found as "live," which increases costs and slows the remediation process. The objective of this project was to demonstrate that PELAN (Pulsed ELemental Analysis with Neutrons) can non-intrusively, non-destructively examine an individual ordnance and confirm whether it contains high explosive (HE).
PELAN is a transportable system, weighing less than 45 kilograms, for the detection of explosives. It is based on the principle that explosives contain various chemical elements such as hydrogen, carbon, nitrogen, and oxygen in quantities and ratios that differentiate them from other innocuous substances. Pulsed neutrons are produced with a pulsed 14 mega (million) electron-volt (d-T) neutron generator. Separate gamma-ray spectra from fast neutron, thermal neutron, and activation reactions are accumulated and analyzed to determine elemental content. Data analysis is performed in an automatic manner, and a final result of whether a threat is present is returned to the operator.
PELAN data was collected on a variety of ordnance sizes, ranging from 60-millimeter (mm) mortars to 155-mm artillary projectiles, that contained either inert or HE filler. For ordnance items greater than 90 mm, PELAN correctly identified 97% of explosive-filled rounds, with a 22% false positive rate. On smaller ordnance, the capability was significantly diminished. Data has been collected to aid future improvements.
There are both economic and safety benefits to be gained from the accurate separation of HE from training rounds. Restricting the application of demolition and associated set back and evacuation procedures to only those items that contain explosives will result in significant cost savings for the Department of Defense. Other benefits of the PELAN system are that it can identify the contents of a shell without touching the object, is not affected by the shell thickness, and can differentiate types of HE or combinations of HE and chemical agents. The signal-to-noise ratio depends on the surrounding materials, and the system relies on a computer library for proper substance identification. (Project Completed - 2004)