Development of 4.2K Cryo-transfer Appratus for Electron Microscope Observation of Low Temperature Neutron-Irradiated Specimens

为了使金属试样在极低温中子辐照后，从辐照低温恒温器冷转移到电子显微镜下观察初发位移级联损伤成为可能，设计并制作了一种新型的低温转移TEM支架。在TEM观察期间，以及在从冷冻转移室到TEM样品室的冷冻转移期间，支架可以在样品位置冷却至9 K。我们所制作的仪器成功地用于在LLNL的RTNS-II上观察了15k D-T中子辐照金属的位移级联损伤的新生状态。预薄的TEM样品用HELI-TRAN低温恒温器辐照。辐照后的低温恒温器被送入我们在这项工作中制造的低温转移室。在不预热试样的情况下，将辐照低温恒温器拆卸在槽内。将样品冷转移到低于18k的低温转移TEM支架中。使用特殊设计的小车移动支架，使样品保持在18k以下并保持清洁。在20 K时用透射电镜观察叶栅损伤结构。在试样加热过程中，观察了位移级联损伤在结构中的松弛过程。

To make possible the observation of nascent displacement cascade damages in metal specimens which are irradiated at very low temperature by neutrons and cold-transferred from irradiation cryostat to electron-microscope, a new type of cryo-transfer TEM holder is designed and fabricated by JEOL. The holder can be cooled down to 9 K at the specimen position during a TEM observation and also during a cryo-transfer from cryo-transfer chamber to TEM specimen chamber. The appratus we fabricated was sucessfully used to observe the nascent state of displacement cascade damages in metals which were irradiated at 15 K by D-T neutrons at RTNS-II in LLNL. Pre-thinned TEM specimens were irradiated using HELI-TRAN cryostat. After the irradiation cryostat was feeded to the cryo-transfer chamber that we fabricated in this work. The irradiation cryostat was dismounted in the chamver without warm-up the specimens. The specimens were cold-transferred to cryo-transfer TEM holder below 18 K. The holder was moved using special designed car keeping the specimen below 18 K and also keeping them clean. The cascade damage structure was determined by TEM observation at 20 K. It was also observed during heat-up of specimens how the displacement cascade damage relax in their structure.