Remote Detection of Concealed Radioactive Materials by Using Focused Powerful Terahertz Radiation

• Published in: Journal of infrared, millimeter and terahertz waves Vol. 37; no. 6; pp. 515 - 535
• Main Author: Nusinovich, Gregory S.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.06.2016; Springer Nature B.V
• Subjects: Breakdown; Classical Electrodynamics; Electrical Engineering; Electromagnetic fields; Electron avalanche; Electron density; Electronics and Microelectronics; Engineering; Free electrons; Instrumentation; Ionization; Power; Pulse duration; Radioactive materials; Terahertz frequencies; Wave propagation; THz breakdown; Propagation of terahertz waves in atmosphere; Air ionization by gamma rays; Focusing of THz wave beams; Terahertz radiation
• ISSN: 1866-6892; 1866-6906
• DOI: 10.1007/s10762-016-0243-3

This review paper summarizes the results of studies of a novel concept of the remote detection of concealed radioactive materials by using focused high-power terahertz (THz) radiation. The concept is based on the known fact that the ambient electron density in air is low (one to three free electrons per cubic centimeter). These electrons can serve as seed electrons from which an avalanche breakdown in strong electromagnetic fields starts. When a powerful THz radiation is focused in a small spot, the breakdown-prone volume can be much smaller than a cubic centimeter. So, the probability of having some free electrons in this volume and, hence, the probability of breakdown are low in the absence of additional sources of air ionization. However, in the vicinity of radioactive materials (10–20 m), the electron density can be higher, and, hence, there are always some seed free electrons from which the avalanche ionization will start. Thus, the breakdown rate in this case can be close to 100 %. Realization of this concept requires studies of various physical and technical issues. First, it is necessary to develop a high-power source of (sub-) THz radiation whose power, frequency, and pulse duration are sufficient for realizing this goal. Second, it is necessary to analyze numerous issues important for realizing this concept. Among these issues are (a) enhancement of the ionization level of air molecules in the presence of hidden radioactive materials, (b) estimating the minimum detectable mass of radioactive material, (c) formation of breakdown-prone volumes in focused THz wave beams, and (d) effect of atmospheric conditions on the propagation and focusing of THz wave beams and on the optimal location of the breakdown-prone volume between a container with hidden radioactive material and a THz antenna. The results of these studies are described below.