Accumulation and collection process of radiation defects by helium ion irradiation

The radiation defects produced by helium ion irradiation were observed. High purity molybdenum and tungsten were irradiated by 5 keV helium ions, and the defects were observed by using a transmission electron microscope. The accuracy of depth measurement was about 1.5nm. At the beginning of irradiation, high density dislocation loops of interstitial atom type were formed. The depth distribution of dislocation loop was similar to the flight range distribution of He+ ions. When the irradiation dose was increased, the He bubbles were produced, and blistering was caused. The bubbles distributed at the depth of two to four times as long as the mean range of He ions. These phenomena supported the gas pressure model of blistering. (Kato, T.)