Progress and Application of Mass Spectrometry Techniques for Single Particle Analysis in Nuclear Safeguard

The nuclear Non-proliferation Treaty (NPT) is one of the cornerstones regulating the international order. To make sure that all the member states fulfill their obligation under the treaty, the International Atomic Energy Agency (IAEA) has constructed a rather sound technological management system, i.e. the nuclear safeguard system. Single particle analysis in wipe samples inside and around nuclear facilities is the main focus of nuclear safeguard and application. The chemical fingerprint information, including 235U abundance, 236U abundance, plutonium content and isotope abundance, fluorine content, chemical composition and form of single particles containing radionuclides (mainly uranium and plutonium) in the micron scale, can reveal the source of materials, processing history, potential use, etc., and then reflect the type of nuclear activities in nuclear facilities, which is of great significance for dealing with the threat of nuclear smuggling and nuclear terrorism to prevent nuclear proliferation. As a powerful technique to analyze the isotopic abundance and ratio of radionuclides, mass spectrometry (MS) is no doubt the core technique in nuclear safeguard. In recent years, the MS technique utilized for single particle analysis has been promoted remarkably. In this review, the principle, technical process, and applications of analytical techniques for chemical compositions, micro morphology, isotope and age analysis of single particle analysis in nuclear safeguards were summarized. Some techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning transmission X-ray microscopy (STXM), micro X-ray rluorescence (MXRF), micro-Raman spectroscopy (MRS), were exploited for studying the chemical composition and morphology of uranium/plutonium-containing single particles. Development and application of techniques for the isotope abundance analysis in uranium or plutonium-contaning single particles, such as secondary ion mass spectrometry (SIMS), thermal ionization mass spectrometry (TIMS), multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), microextraction mass spectrometry (microextraction-MS), were also introduced. The main characteristics, difficulties and limitations of various isotope analysis techniques were emphatically discussed, the unsolved problems and future directions were also prospected.