Abstract: A measurement method for ^239+240Pu in environmental air was established. In this method, about 5 000 to 10 000 m³ air is filtered with NF-2 filter cloth to obtain aerosol sample, the sample is ashed with a dry method, plutonium is leached with hot nitric acid and converted to tetravalent state with Fe(NH₂SO₃)₂ and NaNO₂, the tetravalent plutonium is separated and purified with tri-n-octylamine and polytrifluorochloroethylene, desorbed with 0.025 mol/L oxalic acid and 0.15 mol/L nitric acid. Finally, plutonium is electrodeposited on a stainless plate and measured by an alpha spectrometer. Key conditions and parameters of the measurement method were optimized by experiments as the following: 4 mm of the distance between two poles, 2.0 of pH, 6 cm of the height for the extraction/separation column, 2.0 mL/min of the flow rate of solution, 15 min of the oxidation-reduction time. The radiochemical recovery of plutonium was 52.5% to 82.5% with an average value of 68.3%. The minimum detectable amount was 1.31×10^-7 Bq/m³ when aerosol sample volume was 10 000 m³. It is concluded that this method can be used to measure ^239+240Pu of environmental aerosol samples. The concentrations of ^239+240Pu in aersol samples taken from a northwestern district of China were measured with this method and an average value of 3.25×10^-6 Bq/m³ was obtained.

Key words: aerosol, ^239+240Pu, extraction chromatography, alpha spectrometer