Rapid threat analysis and forensic evidence collection in radiological terror scene using laser-induced breakdown spectroscopy

Abstract

Rapid threat analysis is essential in radiological terror scenes to protect workers and the public. Among the potential materials for radiological explosive devices, $^{90}$Sr is the most likely due to its prevalent use in industrial applications. Unfortunately, the analysis of radioactive Sr is very slow using conventional radiation detection method because $^{90}$Sr emits $\beta$-ray only due to the rigorously interacts with matter and rarely reaches a detector. For detecting Sr onsite, laser-induced breakdown spectroscopy (LIBS) can be an attractive supplementary method. This study investigates the effect of different substrates on identifying Sr physically adsorbed on their surface using single-shot LIBS. The substrates for analysis include metals (aluminium, stainless steels), porous medium (mortar, polyester), and transparent materials (PET). Three chemical compounds, $SrCO_3$, $SrTiO_3$, and $SrF_2$, are selected as the target compounds, based on historical theft cases. Stainless steel exhibits the lowest LOD at 407.77 nm (1.09 $\micro$g/$cm^2$ for $SrCO_3$ and $SrF_2$), with high reliability. To evaluate the reliability of the LOD, the surface distribution, which can affect the reliability, is determined by the sample heterogeneity. In addition, the molecular emissions from the vibrational transition are analyzed, based on the LIBS spectra. Furthermore, the components that must be considered when applied the LIBS technique on-site is discussed and the useful signatures of signal are discovered.