Amorphization of U3Si2 by ion or neutron irradiation

Diffraction techniques have been used to monitor the crystal structure of U3Si2 during irradiation. Neutron diffraction was used to follow crystallographic changes produced by neutron irradiation at 30 C. Neutron irradiation results in uranium fission into energetic fragments that produce tracks of damage in the form of amorphous zones whose volume change relative to the initial lattice produces lattice strains. The total lattice strain increases as the volume fraction of amorphous material increases, and the maximum unit cell volume change is -2.2%. The amorphous volume fraction increases exponentially at an initial rate of (2.24.1022 fissions/m3)-1 or (0.076 dpa)-1, and complete amorphization occurs by a dose of 1.1.1023 fissions/m3 or 0.38 dpa. The unit cell volume decreases linearly with increasing volume fraction of amorphous material, indicating that there is little mechanical yielding or plastic flow during irradiation of amorphous U3Si2. Electron diffraction during in situ 1.5 MeV Kr ion irradiation was used to determine complete amorphization doses for U3Si2 at temperatures above 30 C. As with fission fragments, individual Kr ions produce small amorphous volumes. The temperature limit for complete amorphization is approximately 250 C. Within the uncertainty of the neutron dose steps and damage calculations, the same amount of damage is required for amorphization of U3Si2 by ion or neutron irradiation. (orig.)