High explosives (TNT, RDX, C-4, etc.) are composed primarily of the chemical elements hydrogen, carbon, nitrogen, and oxygen. Many innocuous materials are also primarily composed of the same elements. These elements, however, are found in each material with very different ratios and concentrations. It is thus possible to identify and differentiate, e.g. TNT from other innocuous materials that have the same density.

Table I below shows the atomic density of elements for various materials along with the atomic ratios. Explosives have been shown to be differentiated by the utilization, among others, of both the C/O and the C/N ratios. The problem of identifying explosives is therefore reduced to the problem of elemental identification. Nuclear techniques show a number of advantages for non-destructive elemental characterization. These include the ability to examine bulk quantities with speed, high elemental specificity, and no memory effects from the previously measured object. These qualities are important for an effective detection system for explosives. Neutron-based systems, whereby incident pulsed neutrons excite characteristic gamma-rays of many chemical elements, have been studied as an effective way for the detection of landmines and unexploded ordnance (UXO). (See also detailed description of the PFTNA techniques)

Table I. Elemental densities and ratios of two classes of substances.

A device which is based on pulsed 14 MeV neutrons has been built and is called PELAN (Pulsed ELemental Analysis with Neutrons). PELAN's patent was issued in November 1999.

Over the past 9 years, several tests and evaluations of PELAN have been performed for the detection of explosives (Columbus, Ohio), the detection of hidden drugs (Arizona), for the identification of chemical warfare agents (Poelkapelle, Belgium and Aberdeen, MD), the identification of unexploded ordnance (Indian Head and White Oak), and as a confirmation sensor for humanitarian demining by the International Atomic Energy Agency (IAEA) in Vienna, Austria.

During this time frame, the PELAN has undergone several revisions. Each revision has improved PELAN's performance and portability. Below are images of the PELAN I, PELAN II, and PELAN III developed and built at the Applied Physics Institute. The PELAN IV is the first commercial version of PELAN and is being developed at Science Applications International Corporation (SAIC).

• PELAN I.		• PELAN II.
• PELAN III.

For more detailed information, please see the Publications portion of this web site.