高分辨电感耦合等离子体质谱法测量放射性废液中239Pu与240Pu

Determination of ^(239)Pu and ^(240)Pu for Radioactive Liquid Waste by High Resolution Inductively Coupled Plasma Mass Spectrometry

^(239)Pu和^(240)Pu含量对分析放射性废液来源、选择后续处理工艺十分关键。本研究应用高分辨电感耦合等离子体质谱法(HR-ICP-MS)直接测定放射性废液中的^(239)Pu、^(240)Pu含量。由于^(238) U与1 H结合产生的铀氢复合离子会对^(239)Pu、^(240)Pu造成同质异位素干扰,本研究通过测定铀氢复合离子产率进行质谱干扰修正,将^(239)Pu、^(240)Pu系列浓度标准扣除铀氢复合离子干扰后,分别绘制^(239)Pu、^(240)Pu质量浓度-计数率标准曲线。测量放射性废液样品时,先利用铀氢复合离子产率修正^(239)Pu和^(240)Pu的同质异位素干扰,再将样品计数率值代入标准曲线方程,计算得到放射性废液样品中^(239)Pu和^(240)Pu的质量浓度,最后计算^(239)Pu和^(240)Pu的活度。将质谱法与液闪法测量结果进行比对,结果表明,两者所测结果偏差小于4%,方法相对扩展不确定度为4.6%(k=2)。该方法制样简单,适用于辐射水平高、铀基体含量大的放射性废液中^(239)Pu和^(240)Pu的快速测量。

The accurate determination of concentration of 239Pu and 240Pu is very important not only for estimating the source of radioactive liquid waste,but also for selecting the subsequent disposal strategy.In this paper,a direct method using high resolution inductively coupled plasma mass spectrometry(HR-ICP-MS)to measure the concentration of 239Pu and 240Pu in radioactive liquid waste was proposed.The main problem in the determination of 239 Pu and 240 Pu by HR-ICP-MS is the isobaric interferences caused by uranium(238 U^1H^+and 238 U^1H^2+)which always exists in the radioactive waste liquid with a higher concentration.This work provided a strategy to eliminate these isobaric interferences without separating the uranium from the radioactive liquid waste.Through the measurement of a series of uranium standard solutions with different concentrations by HR-ICP-MS,it was found that the yields of 238 U 1H+and 238 U 1H 2+had positive correlation with the concentration of uranium.Besides,the ratios were constant:r(238 U^1H^+/238 U)=4.85×10-5,r(238 U^1H^2+/238 U)=2.99×10-6.Moreover,after using the yields of 238 U 1H+and 238 U 1H 2+to deduct the isobaric interferences caused by uranium,the measurement results of the 0.1μg/L plutonium standard solution under different uranium matrix interference were roughly equal,indicating that the method to eliminate the isobaric interferences caused by uranium was reasonable and feasible.Furthermore,in order to get the mass concentration-counting rate standard curves for 239 Pu and 240 Pu,a series of the plutonium standard solution at different concentration was also measured.After deducting the isobaric interferences,the mass concentration of 239 Pu and 240 Pu in the samples of radioactive liquid waste could be calculated by the standard curve equation,and then the activity concentration of 239 Pu and 240 Pu in different samples were also calculated.In addition,the results were also compared with those obtained from the liquid scintillation counting method.The deviations between the results from HR-ICP-MS and the liquid scintillation method are less than 4%,and the relative expansion uncertainty is 4.6%(k=2).The proposed method was proved as very effective to overcome the isobaric interferences caused by 238 U 1H+and 238 U 1H 2+with minimal sample preparation(e.g.,no need to separate the uranium),which make it a fast,sensitive and accurate method to analyze 239 Pu and 240 Pu in radioactive waste liquid with abundant uranium existing.