AVS 50th International Symposium
    Homeland Security Topical Conference Wednesday Sessions
       Session HS-WeP

Paper HS-WeP1
Testing Air Jets as Trace Explosive Particle Removers

Wednesday, November 5, 2003, 11:00 am, Room Hall A-C

Session: Poster Session on Science & Technology for Homeland Security
Presenter: R.A. Fletcher, National Institute of Standards and Technology
Authors: R.A. Fletcher, National Institute of Standards and Technology
J.G. Gillen, National Institute of Standards and Technology
E.S. Windsor, National Institute of Standards and Technology
G.A. Klouda, National Institute of Standards and Technology
Correspondent: Click to Email
Detection of trace explosive particles is vital to airport security. One of the key steps in detecting explosive particles is the removal of the particles from the surface that they reside. This can be accomplished by swiping the surface or by energetic disruption such as an air jet that will provide enough force to overcome the particle attachment due to van der Waals forces. Our initial experiments are following the experiments of Phares et al.@footnote 1@ and Smedley et al.@footnote 2@ for polystyrene latex spheres on smooth surfaces. We are utilizing fluorescence tagged spheres of various diameters that we can image through an optical fluorescence microscope. Images of fluorescent particles are captured and recorded before an air jet interrogates the sample. Particle removal is seen in live time; the particles that are not removed from the surface are captured in a subsequent image. Image processing allows us to quickly determine the size distribution the particles that have been removed and the ones that remain. By using polydisperse spheres, we can detect the particle release threshold for a given jet condition in terms of particle diameter. A second study is under way to examine the efficiency of removal for actual high explosives from characteristic surfaces like clothing and luggage. A test substrate is mounted in a small vertically oriented laminar flow wind tunnel. The airflow in the tunnel is hepa filtered to remove all particles greater than 0.3 um diameter. An air jet is used to remove particles from the test surface. The size distribution of the removed particles is determined in real time using a particle detector mounted down stream that works on the basis of measuring particle impact energy. Results from both experiments will be presented.@FootnoteText@@footnote 1@Phares, D.J. et al. J. Forensic Sci. 2000:45;(4) 774-784. 2. Smedley, G.T. et al. Exper. In Fluids 1999:26, 324-334.