Ion microscopy investigation of the impurity trapped interstitials in tungsten

A study was made of the capture of interstitial atoms created by the proton irradiation of tungsten with a raised impurity content. For investigating samples tungsten wire of the VA type with diamter 0.2 mm and 10μm and purity 99.95% was used. The percentages of impurities in this type of tungsten were as follows: K2O - 0.01%; SiO2 - 0.02%; Al2O3 - 0.001%; Fe2O3 - 0.005%; CdO -0.002%; Mo - 0.01%; Ni - 0.001%. Wire with a diameter of 10 μm was at first irradiated with 1.7 MeV protons and then etched for producing samples. The temperature of the samples during the etching process did not exceed 800K, since the sample holder was cooled by liquid nitrogen. While the surface of the tungsten sample was vaporized in layers by a field in the chamber of an electrostatic ion microscope the dependence of concentration of the observed interstitial atoms on the concentration of atoms created by 0.2-1.7 MeV proton irradiation was investigated. It was shown that the impurities in the sample mass were powerful drains for interstitial atoms which were mobile at an irradiation temperature of approximately 780K. (O.M.)