ToF-SIMS spectral analysis of neutron irradiated and unirradiated single crystal tungsten

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) has many promising features in studying materials including high spatial resolution and high mass accuracy of elements, molecules, and isotopes. Its ability to resolve isotopes is especially attractive in studying transmutation products of single crystal tungsten (SCW) post neutron irradiation. Tungsten is a contender of plasma facing materials (PFMs) due to its high thermal and radiological stability. PFMs to be used in the construction of fusion vessels are subject to high temperature and radiological loads, resulting in changes to materials including transmutation, which ultimately impact material mechanical and thermal properties. We used IONTOF TOF.SIMS V instrument equipped with a 25 keV Bi3+ primary ion beam to study of unirradiated SCW and irradiated SCW coupons. Scanning electron microscope coupled with focused ion beam (SEM-FIB) was used to reduce the dosage of neutron irradiated tungsten specimens. Static ToF-SIMS spectra were obtained, and transmutation product peak identification was presented in this work. Identified molecules and molecular fragments were compared against isotope theoretical mass to charge ratios of tungsten, rhenium, osmium, and other relevant products. Our results show that ToF-SIMS provides a viable means to study transmutation products of tungsten.  Such applications are suitable to investigate transmutation effects on structural materials that are being considered and developed for fusion pilot plant.

飞行时间二次离子质谱（Time-of-flight secondary ion mass spectrometry, ToF-SIMS）在材料研究领域具备诸多优异特性，可实现对元素、分子及同位素的高空间分辨与高质量精度检测。其同位素分辨能力在研究中子辐照后单晶钨（single crystal tungsten, SCW）的嬗变产物时极具应用价值。钨因其优异的热稳定性与辐照稳定性，成为面向等离子体材料（plasma facing materials, PFMs）的候选材料之一。用于核聚变装置腔体建造的面向等离子体材料需承受高温与辐照载荷，这会引发材料发生嬗变等变化，最终影响材料的力学与热学性能。本研究使用搭载25 keV Bi3+一次离子束的IONTOF TOF.SIMS V型仪器，对未辐照及经中子辐照的单晶钨试片开展测试，并借助聚焦离子束扫描电镜（Scanning electron microscope coupled with focused ion beam, SEM-FIB）对中子辐照钨试样进行减剂量处理。本研究获取了静态ToF-SIMS谱图，并完成了嬗变产物的峰位指认；将鉴定出的分子及分子碎片与钨、铼、锇及其他相关产物的同位素理论质荷比进行了比对。研究结果表明，ToF-SIMS是研究钨基材料嬗变产物的可行手段，该应用场景同样适用于探究聚变试点工厂正在研发与备选的结构材料的嬗变效应。