CHARACTERIZATION OF DIAMOND SINGLE-CRYSTALS BY MEANS OF DOUBLE-CRYSTAL X-RAY-DIFFRACTION AND POSITRON-ANNIHILATION

The crystallinity of synthesized and natural crystals of diamond was c haracterized by double-crystal X-ray diffraction and positron annihila tion. The two-dimensional angular correlation of annihilation radiatio n and positron lifetime measurements revealed that in natural crystals positroniums are formed in a high fraction. The synthesized crystal I b showed both an extremely small width for the diffraction and a posit ron lifetime spectrum with a single component of the lifetime of 115 p s. In contrast, the natural diamonds contain a long-lived component of lifetime longer than 2 ns. The diffusion length of positrons was also measured by a variable-energy positron beam. In the synthesized cryst al IIa, a diffusion length of about 100.8 nm was observed.