Laser Desorption of Traces of Explosives in Ion Mobility Spectrometry

The efficiency of a YAG:Nd3+laser (λ = 1064 nm) and a diode continuous laser (λ = 440 nm) to initiate laser desorption of traces of trinitrotoluene (TNT) and cyclotrimethylenetrinitramine (RDX) is quantitatively compared with use of mass spectrometry. It is shown that a pulsed neodymium laser is more promising for creating a device of contactless sampling for ion mobility spectrometers

Surface ligands affect photoinduced modulation of the quantum dots optical performance

ABSTRACT Changes of optical properties of the solutions of CdSe/ZnS quantum dots (QDs) covered with the trioctylphosphine oxide (TOPO) ligands under the pulsed ultraviolet (UV) laser irradiation are observed. The fluorescence quantum yield (QY) of QDs decreases by more than an order of magnitude when the radiation dose approaches 2 × 10 -15 J per particle. This process is accompanied by a blue shift of both fluorescence and the first excitonic absorption peaks. The fluorescence quenching becomes less pronounced when the overall TOPO content in the solution is increased. When ТОРО ligands are replaced with n-hexadecylamine (HDA), QY and spectral properties are not changed at the same irradiation conditions. We assume that the above changes of the optical properties are associated with photooxidation of TOPO ligands by excited QD. Such process is less probable for the HDA ligand due to its different energy structure

Contemporary Conditions of Economic Competition Between the USSR and the USA

The competition between the Soviet Union and the United States of America has been taking place during the past few years in a complex international atmosphere under changing conditions of economic development in both countries.

Gross Agricultural Output of the USSR and the USA

One of the conditions for a correct assessment of the course of the economic competition between the two (socialist and capitalist) systems and of the prospects of its development is a reliable scientific comparison of USSR and U. S. farm output.

Dissociation of Trinitrotoluene on the Surface of Porous Silicon Under Laser Irradiation

AbstractDissociation of trinitrotoluene (TNT) sorbed on porous silicon (pSi) surface under UV laser irradiation has been studied. A method based on ion mobility spectrometry (IMS) has been used in this study. Excitation and ionization of TNT molecules has been occurred at atmospheric pressure. A dependence of TNT ion spectrum on standing time of TNT molecules on pSi surface has been demonstrated. The ion type has changed from (TNT-H) – to (TNT-NO2) – which indicates a slow chemical reaction between pSi surface and TNT molecules. The first step of (TNT-NO2) – formation has been found to be a result of laser stimulated surface dissociation and subsequent desorption of a neutral TNT-NO2 fragment. The second step of (TNT-NO2) – formation is a capture of an electron emitted from the pSi surface under laser irradiation. The result of this study could be used in the area of explosive detection

Enhancement of Characteristics of Field Asymmetric Ion Mobility Spectrometer with Laser Ionization for Detection of Explosives in Vapor Phase

Ion mobility spectrometry instrumentation today is widespread in the area of transport security and counterterrorism. This method of detection of explosive substances is highly appreciated for the existence of portable detectors capable of detecting concentrations of 10−13–10−14 g/cm3 at atmospheric pressure using traditional ionization methods including corona discharge and beta radiation. However, low vapor pressure of some explosives imposes requirements on limit of detection (LOD) down to 10–15‒10−16 g/cm3. In this paper we compare a radioactive 63Ni ionization source with a laser ionization source and reveal the parameters of laser ionization of a group of explosives, namely trinitrotoluene (TNT), cyclotrimethylene-trinitramine (RDX), cyclotetramethylene-tetranitramine (HMX) and pentaerythritol tetranitrate (PETN), which can reduce the limit of detection of portable devices. A laser ionization source can provide a higher signal to noise ratio than radioactive 63Ni at optimal intensity of laser radiation for PETN and HMX of 3 × 107 W/cm2 and 2.5 × 107 W/cm2, respectively. Limits of detection were estimated: 3 × 10−15 g/cm3 for RDX, 8 × 10−15 g/cm3 for PETN and less than 3 × 10−15 g/cm3 for HMX. These results are promising to further improve the capabilities of detectors of low volatility explosives without sacrificing portability, light weight and reasonable cost of the laser source