MODELS IN PHYSICS AND TECHNOLOGY

Study of the possibility of detecting traces of hazardous substances based on vapor detection

O. B. Kudryashova, A. B. Vorozhtsov, Yu. M. Mikhailov

National Research Tomsk State University, 36 Lenin ave., Tomsk, 634050, Russia

Abstract: The article investigates the possibility of detecting traces of hazardous substances (explosives and narcotics) based on the detection of their vapors in the air. The relevance of the study stems from the need to counter terrorist threats and drug trafficking, where identifying even trace amounts of substances is critical. The focus is on mathematical modeling of the evaporation of a thin substance layer from a surface, based on molecular kinetic theory. A universal model is proposed, accounting for the physicochemical properties of substances, ambient temperature, adhesion to the surface, and the initial mass of the layer. Using the Hertz – Knudsen – Langmuir and Clausius – Clapeyron equations, analytical expressions are derived for the complete evaporation time, maximum vapor mass, and process dynamics. A dimensionless parameter, $\gamma$, is identified, determining the limiting conditions for evaporation. It is shown that substance adhesion (coefficient $\alpha$) affects the evaporation rate but not the final vapor mass. Calculations were performed for six model substances (TNT, RDX, PETN, amphetamine, cocaine, heroin) with a wide range of properties. At room temperature and a surface concentration of 100 ng/cm$^{2}$, most substances evaporate completely, except for RDX, which remains on the surface at 84%. Evaporation times range from fractions of a second (amphetamine) to several hours (heroin). For low-volatility substances, the maximum mass capable of evaporating under given conditions is determined. The novelty of the work lies in the development of a universal model applicable to a broad class of hazardous substances and in identifying key parameters governing the evaporation process. The results enable the estimation of detection limits for trace substances using vapor-based methods and can be applied in the design of security systems.

Keywords: thin layer, evaporation, hazardous substances, vapor mass, surface concentration, mathematical model

UDC: 51-73

Received: 25.04.2025
Revised: 10.05.2025
Accepted: 27.05.2025

DOI: 10.20537/2076-7633-2025-17-3-451-463