Small-Angle Scattering of X-Rays by Neutron-Irradiated Germanium

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Abstract
A study has been made of neutron‐irradiated germanium single crystals by measuring the small‐angle scattering of x‐rays. The magnitude of the observed scattering is found to be strongly dependent on the crystallographic orientation of the specimen with respect to the direction of the incident x‐ray beam. The scattering can be explained in terms of double‐Bragg scattering and is believed to be due to lattice strain associated with the radiation‐induced defects. The results imply that the damaged regions (spikes) which in addition to point defects are produced by the bombarding neutrons have a disordered (possibly amorphous) structure with a density which differs from that of the surrounding matrix by at most a few percent. Annealing measurements reveal a distinct annealing stage centered at about 160°C in which approximately 60% of the small‐angle scattering recovers. The activation energy of this stage is found to be 1.2 eV and is associated with the annihilation of either vacancies or divacancies. The annealing of the remainder of the small‐angle scattering in the temperature range above 350°C is attributed to the recovery of the damaged regions.