Analytical Methods For ²³⁸Pu/^239,240 Pu Activity Ratio In Environmental Samples

The characteristic of the 238Pu/239,240Pu activity ratio in environment samples around nuclear facilities can be used to assess the nuclear activities.In order to obtain an accurate isotope ratio,analytical methods for 238Pu/239,240Pu activity ratio need to be established.In this work,two typical environmental samples of soil and plant were investigated to establish analytical methods for 238Pu/239,240Pu activity ratio.The problems of counting interference of 228Th,241Am to 238Pu and 210Po to 239,240Pu were solved by introducing co-precipitation,increasing the amount of acid solutions and resin combination.The feasibility of TOA extraction chromatography,AG 1×8 resin,TEVA resin on 238Pu/239,240Pu activity ratio analysis were evaluated with the focus on the removal of impure elements such as U,Th,Am,Po and the minimum detection activity concentration.Based on these,new produres for determination of 238Pu/239,240Pu activity ratio were developed.Firstly,analytical methods for 238Pu/239,240Pu activity ratio using TOA extraction chromatography,AG 1×8 resin and TEVA resin in soil samples were developed.For 25 g soil sample,the chemical recoveries of Pu of TOA extraction chromatography and TEVA resin are greater than 70%,and the chemical recovery of Pu of AG 1×8 resin is greater than 80%.The decontamination factors of U,Th and Am for TOA extraction chromatography are greater than 104,104 and 103,respectively,and the decontamination factors of U,Th and Am for AG 1×8 resin and TEVA resin are all greater than 104.The minimum detection activity concentrations of 238Pu are(6.0±1.6)mBq/kg,(8.8±0.8)mBq/kg and(8.0±0.8)mBq/kg,respectively.The minimum detection activity concentrations of 239,240Pu are(6.4±0.4)mBq/kg,(9.6±1.2)mBq/kg and(9.6±2.8)mBq/kg,respectively.Although the TOA extraction chromatography needs to be prepared manually and the flow rate is relatively slow,the minimum detection activity concentrations of 238Pu and 239,240Pu in the TOA extraction chromatography are lower than that of the other two resins.Secondly,analytical methods for 238Pu/239,240Pu activity ratio using AG 1×8 resin,TEVA resin and TOA-TRU resin in plant samples were developed.In the TOA-TRU resin,the impure elements U,Th and Am were removed by TOA extraction chromatography,and the impure element Po was removed by TRU resin.For 10 g plant sample,the chemical recoveries of Pu of AG 1×8 resin and TEVA resin are greater than 80%,the chemical recovery of Pu of TOA-TRU resin is greater than 60%,and the decontamination factors of Th,Am,Po and U are greater than 104,104,104 and 102,respectively.The minimum detection activity concentrations of 238Pu are(22±2)mBq/kg,(20±2)mBq/kg and(22±5)mBq/kg,respectively.The minimum detection activity concentrations of 239,240Pu are(24±3)mBq/kg,(24±7)mBq/kg and(27±6)mBq/kg,respectively.These methods can be widely applied to the analysis of 238Pu/239,240Pu activity ratio in environmental soil and plant samples and thus provide technical support for arms control verification and environmental monitoring.