High-precision Isotope Analysis Of Cerium-neodymium By Thermal Ionization Mass Spectrometry And Origin Assessment Of Uranium Ores Based On Rare Earth Elements

The phenomenon of nuclear smuggling and illicit trafficking of nuclear material has led to the development of a new branch of science—nuclear forensics.The key issue of nuclear forensics is the identification of the origin of the seized or found nuclear materials.The contents or isotope ratios of trace elements,which have been widely applied in geochemistry and geochronology,are recently recognized to be a potential signature for tracing the origin of nuclear-related materials.In this paper,rare earth elements(REEs)in uranium ore samples were measured by inductively coupled plasma mass spectrometry(ICP-MS).The combined chemical separation procedure of Nd-Ce in uranium ore was established by using AG 50W-X12 resin and Ln resin,which not only realized the separation of rare earth elements from complex matrices,but also effectively removed the interference elements.High-precision measurement methods of Nd and Ce isotopes in uranium ore were established using thermal ionization mass spectrometry(TIMS).The analytical methods were verified by repeated measurements of reference isotope materials and reference rock samples,and then the Nd and Ce isotopes in uranium ore samples were measured.Finally,based on the contents of rare earth element and the Nd and Ce isotopic ratios obtained in the uranium ore samples,we traced the origins of uranium ore samples with the help of multidimensional statistical methods,such as the cluster analysis(CA),principal component analysis(PCA),principal component-cluster analysis(PCA-CA)and linear discriminant analysis(LDA)methodsThe main research contents and results are as follows(1)A method for measuring the contents of rare earth elements in uranium ore samples by ICP-MS was established.The working parameters of the instrument were determined,and the detection limits of the method and procedure blanks were examined.The established analytical method was used to measure the contents of rare earth elements in uranium ores.The results show that the contents of the same rare earth element in uranium ore samples from different countries varie greatly.At the same time,the contents of the same rare earth element in uranium ore samples from the same country are quite different as well.These results provide a data basis for subsequent geological traceability analysis of uranium ore samples(2)The combined chemical separation procedure of Nd-Ce in uranium ore was established The main matrix elements and interfering impurities are eluted with AG 50W-X12 resin,then the Ce component in the light rare earth elements is eluted by the redox method,and the Nd component is further obtained by leaching with Ln resin.The results show that the procedure blanks of Ce and Nd are 0.4-2.9ng and 0.02-0.12ng,respectively.The recovery of Ce in the final solution is about 88%-96%,and the recovery of Nd is about 81%-90%.The concentrations of the main interfering rare earth elements are extremely low,and the decontamination effect of the chemical separation could meet the requirements of high-precision mass spectrometry measurements.(3)A high-precision TIMS analysis method for Nd isotope ratio by Nd+technique was established.A new film porous ion emitter(FPIE)was prepared,and the ionization behaviors of Nd under FPIE conditions were studied.The results showed that the Nd+ion yield of the FPIE method was increased by about 10 times compared with the traditional double Re filament method.The accuracy and precision of the newly-established method were verified by measuring the 43Nd/144Nd ratios of reference isotope material JNdi-1 and reference rock samples.Then the method is used to analyze Nd isotope ratios in uranium ore samples,and the external precision of the 143Nd/144Nd ratio could reach 35ppm(4)A high-precision TIMS analysis method for Ce isotope ratio by Ce+technique was established.It have been shown that,compared with traditional double Re filaments,the ionization efficiency of Ce+ions is significantly higher than that of CeO+ions under FPIE conditions.It was found that the employment of TaF5 as an activator significantly suppress the Ba+isobaric interference signal by generating BaF+ions,thus it is beneficial to analyze the Ce isotope ratio using Ce+technique.The optimized 1013-1012-1010 ? current amplifier combination was determined by comparing the Ce isotope ratios under different combinations of current amplifier.The external accuracy of the measured 138Ce/140Ce ratios reached 36 ppm.Compared with the traditional 1011 ? amplifier,the external precision of the 138Ce/140 Ce ratio is increased by about 8 times,which is comparable to that obtained by the CeO+techniques.(5)Based on the obtained rare earth element contents and Nd,Ce isotope information in the uranium ore samples,multidimensional statistical methods such as CA,PCA,PCA-CA,and LDA were used to carry out geographical traceability research on uranium ore samples from different sources.The results show that most of the multidimensional statistical methods established behave well in accuracy and reliability,and different multidimensional statistical methods have their own applicable scenarios.In addition,compared to using only the rare earth element content as the traceability information,the traceability effect significantly improve when combining the rare earth element content with the Nd-Ce isotope information.It is further proved that multidimensional statistical methods,which based on the rare earth element contents and the Nd-Ce isotope information,are powerful tools for the nuclear forensic investigation to identify the geographical source of unknown nuclear materials.