Use of Anomalous X-Ray Transmission for the Detection of Defects Produced in Silicon and Germanium by Fast Neutron Irradiation

Abstract

Absolute x-ray intensities anomalously transmitted through fast-neutron-irradiated silicon and germanium crystals have been measured and compared with those transmitted through nearly perfect (unirradiated) crystals. The results indicate that the Borrmann intensities in both silicon and germanium irradiated with 4×1019 fast neutrons/cm2 (E>0.6 MeV) were reduced by nearly a factor of two for μ0t0≈30. In contrast, very small (<5%) decreases in the Bragg intensities diffracted from the surfaces were observed. The observed decreases in intensity have been attributed to the strains in the vicinity of ``disordered regions,'' previously observed in electron-microscopy studies of irradiated germanium. Isochronal annealing studies have demonstrated that the crystals could be restored to near their original state of perfection by heating to ≈700°C for 30 min. Two well-defined annealing peaks were found in both kinds of crystals, silicon annealing at about 190° and 630°C, and germanium at about 150° and 400°C. These studies suggest that fast-neutron doses at ambient temperature in the range of 1019–1020/cm2 (E>0.6 MeV) are necessary for observations of appreciable effects on the x-ray intensities diffracted from silicon and germanium.