FORMATION AND ANNEALING OF RADIATION DAMAGE IN NEUTRON-IRRADIATED NATURAL TYPE Ia DIAMONDS

10.25712/ASTU.1811-1416.2026.01.001

Abstract

Optical spectroscopy was used to study a collection of natural type Ia diamonds subjected to neutron irradiation followed by vacuum annealing. The dominant atomic defects (centers) in the diamond structure were determined as functions of the irradiation dose and subsequent annealing temperature. It was determined that a high-quality crystalline medium with the most intense H3 luminescence and a minimum content of other optically active defects can be obtained from pure type IaA diamond (with Na ≈ 200 ppm) by neutron irradiation with a dose of D_N = 0.2×10¹⁷ cm^-2 in combination with subsequent high-temperature annealing in vacuum. A threshold value of the product of the irradiation dose and the total nitrogen content in the crystal was found, above which, upon annealing at 1500º C, due to sequential transformation of defects, about 4 ppm of C defects appear in the crystal lattice, amounting to 380∙10¹⁷ ppm×neutrons/cm². The following are characteristic for neutron irradiation: a) the H1g system (~ 4444 cm^-1 or ~ 2250 nm); b) a doublet of narrow absorption lines (80K) at 638/643 nm; and c) a system in the near-IR range with a line at 913 nm.