Identifying uranium particles using fission tracks and microsampling individual particles for analysis using thermal ionization mass spectrometry.

The analysis of isotope ratios in individual particles found in the environment is important to clarify the origins of the particles. In particular, the analysis of uranium particles in environmental samples from nuclear facilities is useful for detecting undeclared nuclear activities related to the production of nuclear weapons. Thermal ionization mass spectrometry (TIMS) combined with a fission track technique is an efficient method for determining the isotope ratios of individual uranium particles, but has a drawback called "particle-mixing". When some uranium particles are measured as a single particle and an average isotope ratio for the particles is obtained, it is called "particle mixing". This may lead to erroneous conclusions in terms of the particle sources that are identified. In the present study, microsampling using a scanning electron microscope was added to the fission track-TIMS procedure. The analysis of a mixture of SRM 950a and CRM U100 reference materials containing uranium particles indicated that particle mixing was almost completely avoided using the proposed technique. The performance of the proposed method was sufficient for obtaining reliable data for the sources of individual particles to be identified reliably.