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

A simple and sensitive method was developed for Pu-239,Pu- 240 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 Pu-239 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 x10(-16) g (0.34 mu Bq) for Pu-239 and 9 x10(-17) g (0.8 mu Bq) for Pu-240, demonstrating the feasibility of AMS for the determination of the sub-femtogram level of Pu-239,Pu-240 in environmental grass with global fallout signatures. Grass samples collected from China natural environment were successfully analyzed, and Pu239+240 concentration down to 1.6 x10(-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.