Studies on Re-emission Behavior of Hydrogen Isotopes from Wall Materials by Means of Ion Beam Analysis Techniques

本项目的目标是阐明墙体材料中氢同位素再释放的基本过程，并建立描述其在墙体材料中动态行为的模型，以预测和评价He排放和主排放过程中氢同位素的再循环。1990年和1991年，1）采用弹性反冲探测技术，在室温下，以6 × 10 ^ /cm ^2·s的注量，测量了注入过程中和注入后石墨中氢同位素的深度分布<15>。2）在室温到250 ℃的温度范围内，测量了3 keV H^+或D^+离子注入到饱和状态后，1.5MeV He^+离子轰击石墨引起的氢同位素浓度衰减。已经发现， ...更多信息 H浓度比D浓度快。这种同位素差异可以用离子诱导的去俘获截面的同位素差异以及激活氢和俘获氢之间的局部分子复合和再俘获的速率常数之比来解释。3）用3 keV的H^+或D^+离子束注入石墨，在450 ~ 600 ℃范围内测量了等温退火引起的H浓度的衰减，发现H浓度的衰减比D浓度的衰减快。这种同位素差异也可以用热脱陷、再俘获和活化氢分子间局域复合的速率常数的异位性差异来解释。4）利用再发射实验中获得的再发射谱，用描述氢同位素动力学行为的质量平衡方程，从理论上预测了氢同位素注入石墨后的热脱附谱。结果表明，当采用等温再发射实验中得到的物理参数时，氢分子的热脱附谱计算值与实验值吻合较好。少

Goal of this project is to clarify the elementary processes in the re-emission of hydrogen isotopes from wall materials and to establish the model describing their dynamic behavior in the wall materials for prediction and evaluation of hydrogen isotopes recycling during He discharge and main discharged.In 1990 and 1991, we have performed following tasks for graphite materials concerning with this project.1) Depth profiles of hydrogen isotopes in graphite during and after implantation at flux of 6x10^<15>/cm^2s at room temperature have been measured by means of the elastic recoil detection technique. It has been found from comparison between both depth profiles that dynamic retention of hydrogens in graphite is so small not to be detected.2) The concentration decays of hydrogen isotopes in graphite, implanted with 3 keV H^+_ or D^+_ ion beams up to saturation, induced by 1.5 MeV He^+ ion bombardment have been measured at temperatures from RT to 250ﾟC. It has been found that the decay of … More H concentration is faster than of D concentration. This isotopic difference is shown to be explained in terms of isotopic difference in the ion-induced detrapping cross-section and the ratio of the rate constants of local molecular recombination between an activated hydrogen and a trapped one and retrapping.3) The concentration decays of hydrogen isotopes in graphite, implanted with 3 keV H^+_ or D^+_ ion beams up to concentration, induced by isothernal annealings have been measured at temperatures from 450 to 600ﾟC It has been also found that the decay of H concentration is faster than that of D concentration. This isotopic difference is also shown to be explained in terms of istopic difference in the rate constants of thermal detrapping, retrapping and local molecular recombination between activated hydrogens.4) Using the re-rmission profiles obtained in the re-emission experiment, it is shown that the thermal desorption spectrum on hydrogen isotopes implanted into graphite is theoretically predicted using the mass balance equations describing their dynamic behaviors. It is found that the calculated thermal desorption spectrum of hydrogen molecule agrees well with the experimental ones when the physical parameters obtained in the isothermal re-emission experiment are used. Less