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

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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.