【摘要】 TIMS分析超痕量Pu同位素丰度比中本底干扰不容忽视,分析认为干扰可能源自离子源中样品载带材质Re与带中相关杂质元素结合形成的双原子分子离子.为了证明这种认识的合理性,首先采用Gaussian03程序,选用密度泛函方法和LANL2DZ基组计算了CrRe~+、FeRe~+分子离子的结构、势能曲线以及热力学性质等,从理论角度提出CrRe~+、FeRe~+两种分子离子能够稳定形成并稳定存在的可能性.其次,在热表面电离质谱计样品载带中分别承载Cr、Fe样品,扫描了质量数237～243范围的谱图,发现在相应质量数位置有离子流,幅度大于空白本底.理论计算结果和实验验证结果表明:在质量数237～243范围的空白本底应该源自载带材质Re与带中杂质元素Cr、Fe结合形成的双原子分子离子.这为实验中采用何种措施减小本底干扰提供了参考.更多还原

【Abstract】 The background interference can not be neglected during the analysis of trace amount Pu isotopic abundance ratio.Previous works did not indicate perfectly the source of background interference. New interpretation of source has been put forward in this article,which background maybe come from the combination of Re ion with impurity elements Cr,Fe of metal Re filament for sample,and the verification has also been carried out from the theoretical and experimental aspects.Firstly,the structure, potential energy and the thermodynamic parameters of CrRe~+、FeRe~+ ions have been simulated through Gaussian03 Program,and the calculation result means that these ions can exist after forming.Secondly, the spectrum from mass range 237 to 243 has been scanned by TIMS after sampling Cr,Fe respectively, the mass spectrum figures show that the intensities of corresponding peaks from sample filament is larger than those from blank filament.Therefore,a conclusion can be drown that the background interference source in the mass range of 237 to 243 should be the diatomic compound molecule,which are the combination between the metal Re ions and impurity elements Cr,Fe of sample filament during the trace amount Pu isotopic abundance ratio analysis.This study can help us to take measurement to reduce the background interference and increase the accuracy of experimental data.更多还原