Studies of the laser-induced fluorescence of explosives and explosive compositions.

Abstract

Continuing use of explosives by terrorists throughout the world has led to great interest in explosives detection technology, especially in technologies that have potential for standoff detection. This LDRD was undertaken in order to investigate the possible detection of explosive particulates at safe standoff distances in an attempt to identify vehicles that might contain large vehicle bombs (LVBs). The explosives investigated have included the common homogeneous or molecular explosives, 2,4,6-trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN), cyclonite or hexogen (RDX), octogen (HMX), and the heterogeneous explosive, ammonium nitrate/fuel oil (ANFO), and its components. We have investigated standard excited/dispersed fluorescence, laserexcited prompt and delayed dispersed fluorescence using excitation wavelengths of 266 and 355 nm, the effects of polarization of the laser excitation light, and fluorescence imaging microscopy using 365-and 470-nm excitation. The four nitro-based, homogeneous explosives (TNT, PETN, RDX, and HMX) exhibit virtually no native fluorescence, but do exhibit quenching effects of varying magnitude when adsorbed on fluorescing surfaces. Ammonium nitrate and fuel oil mixtures fluoresce primarily due to the fuel oil, and, in some cases, due to the presence of hydrophobic coatings on ammonium nitrate prill or impurities in the ammonium nitrate itself. Pure ammonium nitrate shows no detectable fluorescence. These results are of scientific interest, but they provide little hope for the use of UV-excited fluorescence as a technique to perform safe standoff detection of adsorbed explosive particulates under real-world conditions with a useful degree of reliability. LDRD Studies of the Laser-Induced Fluorescence of Explosives and Explosive Compositions4

Development and application of a high-speed planar laser-induced fluorescence imaging system to evaluate liquid and vapor phases of sprays from a multi-hole diesel fuel injector

“…For this work, common diesel fuel was utilized along with ultraviolet excitation; therefore, a fluorescent dopant was not required. With 266 nm excitation, diesel fuel LIF emission generally peaks between 350 and 375 nm and exhibits a long wavelength tail extending well into the visible range [12]. LIF emission is primarily due to the presence of polycyclic aromatic hydrocarbons [12].…”

“…With 266 nm excitation, diesel fuel LIF emission generally peaks between 350 and 375 nm and exhibits a long wavelength tail extending well into the visible range [12]. LIF emission is primarily due to the presence of polycyclic aromatic hydrocarbons [12]. In particular, it is believed that the primary contributors include alkylated naphthalenes and phenanthrenes, with fluoranthenes and anthracenes contributing at longer wavelengths [12].…”

“…LIF emission is primarily due to the presence of polycyclic aromatic hydrocarbons [12]. In particular, it is believed that the primary contributors include alkylated naphthalenes and phenanthrenes, with fluoranthenes and anthracenes contributing at longer wavelengths [12].…”