Determination of ultra-low level of ^{239, 240}Pu in grass/vegetable sample by compact accelerator mass spectrometry

Abstract

A simple and sensitive method was developed for ^{239, 240}Pu determination of sub-femtogram level in grass/vegetable sample using compact accelerator mass spectrometry (AMS). Pu was leached with HNO₃-H₂O₂ after ashing, and purified with AGMP-1 M resin column from grass matrix. After target preparation using mixed titanium/iron oxides, the final sample was measured by 300 kV AMS. The average recovery was higher than 80% for large-size (> 20 g ) grass sample in the entire procedure. 20 g environmental grass samples spiked with known amounts of ²³⁹Pu standard solution or certified reference materials were measured for method evalution, good agreement between the expected values and measured results has been achieved. The detection limits were estimated to be 1.5 × 10^–16 g (0.34 µBq) for ²³⁹Pu and 9 × 10^–17 g (0.8 µBq) for ²⁴⁰Pu, demonstrating the feasibility of AMS for the determination of the sub-femtogram level of ^239,240Pu in environmental grass with global fallout signatures. Grass samples collected from China natural environment were successfully analyzed, and ^239+240Pu concentration down to 1.6 × 10^− 4 Bq/kg were measured in these samples. This improvement can stimulate environmental monitoring, ecological migration process and biological availability studies of Pu in the biosphere.