Determination of 240Pu/239Pu, 241Pu/239Pu and 242Pu/239Pu isotope ratios in environmental reference materials and samples from Chernobyl by thermal ionization mass spectrometry (TIMS) and filament carburization

Abstract

In various areas such as e.g. nuclear safeguards, environmental monitoring, nuclear forensics, precise, sensitive and accurate plutonium analysis are needed. Plutonium isotope ratios are used as “fingerprints” in revealing different sources of plutonium contamination in the environment. In this study, ²⁴⁰Pu/²³⁹Pu, ²⁴¹Pu/²³⁹Pu and ²⁴²Pu/²³⁹Pu isotope ratios were determined in four different reference materials and samples from Chernobyl using Thermal Ionization Mass Spectrometry (TIMS) in combination with multiple ion counting (MIC) and filament carburization. After the samples were leached with 8M HNO₃, plutonium was co-precipitated on CaC₂O₄ and separated from interfering radionuclides and matrix elements by anion exchange and extraction chromatography (TEVA Spec). The purified plutonium solution was loaded on carburized Re filaments for TIMS measurements. Filament carburization using benzene gas as a pure carbon source was applied in order to enhance the efficiency of plutonium for the mass spectrometric analysis. The TIMS measurements were performed using a multiple ion counting (MIC) detection system using both multi-dynamic and static measurement modes. The analytical procedure was validated using various reference materials and further applied to soil and moss samples from Chernobyl. The obtained ²⁴⁰Pu/²³⁹Pu isotope ratios for reference materials were in good agreement with the literature values. Due to the newly developed techniques and procedures, data not only for the ²⁴⁰Pu/²³⁹Pu “major” isotope ratios but also for the first time ²⁴¹Pu/²³⁹Pu and ²⁴²Pu/²³⁹Pu “minor” isotope ratios were acquired with lower uncertainties, which is particularly important for fingerprinting of environmental samples in nuclear safeguards.