Di-interstitial formation within small defect cascades in aluminium

The increase of the effective concentration of interstitial traps with increasing Frenkel defect concentration has been investigated in pure Al samples irrdiated at 55 K with 1 MeV and 3 MeV electrons. The increase of the trap concentration per Frenkel defect produced was found to be larger for the 3 MeV than for the 1 MeV irradiation. The difference is ascribed to di-interstitial formation within the small cascades produced by 3 MeV electron irradiation. For the cascades containing two to five Frenkel defects it was found that in the average about 12% of the interstitials produced within these cascades encounter upon migration and form di-interstitials. (author)