Development of In Situ RBS Technique for Measurement of Sorption and Dissolution at the Liquid-Solid Interface

本项目的目标是研制一套能测量重核素在液-固界面上吸附和溶解的原位RBS系统，并根据所研制的RBS系统所测得的速率常数阐明液-固界面上吸附和溶解的基本过程。该装置通过差动抽运线与日本原子力研究所TIARA装置中的3 MeV串列加速器的束线相连，并研制了一种原位RBS系统，用于测量吸附在液体容器薄膜窗内表面的重核素的深度分布，用9 MeV的He^<++>离子束照射。此外，在靶室中安装了样品组件，并建立了用于制造直径为3 mm、厚度为5 μ m的较薄窗口、厚度为0.4mm和10 mm的硅晶片盘的方法。测定了沉积在SiO_2表面的Pb原子在不同pH值的HNO_3或NH_4水溶液中的溶解速率常数。3OH被稀释溶解。名古屋大学在硅窗口的SiO_2表面淀积了Pb层，并测量了Pb层的厚度。原位背散射技术发现，在pH=7以上的碱性水和超高纯水中，SiO_2表面的Pb原子几乎不溶于水，而在pH=5的酸性水中，Pb原子溶解，Pb层厚度随暴露时间的增加而线性减小。结果表明，铅在酸性水中的溶解为零级动力学过程。因此，Pb原子从SiO_2表面均匀地溶解到酸性水中。

Goal of this project is to develop an in-situ RBS system for measurement of sorption and dissolution of heavy nuclides at the liquid-solid interface and to clarify elementary processes for the sorption and dissolution at the liquid-solid interface based on their rate constants obtained using the system developed.In 1996 and 1997, we have performs following tasks concerning this project.In 1996, a target chamber, with which an emergent shutter moving quickly and electrically is equipped for vacuum protection, has been connected to a beam line, through a differentially pumped line, of the 3MeV tandem accelerator in TIARA facilities of JAERI and an in-situ RBS system has been developed in order to measure the depth distribution of heavy nuclides adsorbed at the inner surface of a thin film window of a liquid container, which is irradiated with a probing 9MeV He^<++> ion beam. Moreover, in the target chamber a sample assembly has been installed, and the method for fabricating a thinner window of 3mm in diameter and of 5mum in thickness the silicon wafer disks of 0.4mm in thickness and of 10mm in thickness has been established.In 1997, the rate constants of dissolution of Pb atoms deposited on the SiO_2 surface into water solutions with different values of pH in which HNO_3 or NH_3OH are dilutely dissolved. Deposition of Pb layrs onto the SiO_2 surface of the silicon window and measurement of the Pb thickness were done in the Nagoya University. It has been found by the in-situ RBS technique that Pb atoms at the SiO_2 surface are hardly dissolved into both water in ultra high purity and alkaline water above pH=7, while Pb atoms are dissolved in acid water with pH=5 and that the thickness of Pb layrs decreases linearly with increasing the exposure time. This result indicates that the dissolution of Pb atoms into the acid water is the zero-th order kinetics. Therefore, it is concluded that Pb atoms are uniformly dissolved from the SiO_2 surface into the acid water.