The formation of interstitial dislocation loops under He+ bombardment was studied by means of transmission electron microscopy. Wedge-shaped specimens of the pure metal were subjected to bombardment with 5 to 100keV ions at temperatures of between 300 and 570K. It was found that the minimum thickness, within which interstitial loops formed, increased with increasing ion energy and irradiation temperature, but this thickness hardly depended upon the dose rate. The loop density exhibited a linear dependence upon dose after bombardment with 20 or 30keV ions, but exhibited a higher-order dependence after bombardment with 5 or 10keV ions. On the basis of the results, it was concluded that a low fraction of high-energy primary knock-on atoms played an important role in the nucleation of interstitial loops at energies above about 20keV.

K.Yasuda, C.Kinoshita, M.Kutsuwada, T.Hirai: Journal of Nuclear Materials, 1996, 233-237B, 1051-6