A comparison of diamonds irradiated by high fluence neutrons or electrons, before and after annealing

Neutron- and electron-irradiated type Ia “black” diamonds were analyzed: three near colorless type Ia diamonds were treated in a nuclear reactor with a dose of 1.8 × 1017 neutrons/cm2 and three equivalent samples were irradiated in an electron accelerator with a dose of approximately 0.5 GGy 10 MeV electrons. The diamonds were then annealed and analyzed after the different steps of the treatment. The samples turned from near colorless to very dark green to opaque black upon irradiation and deep greenish yellow to deep orangy brown upon annealing (Fig. 1). The amount of brown color developed during the treatment was found to relate to the type of irradiation used and likely to the total dose of irradiation. The absorption and photoluminescence features as well as the color changes that were observed were found to be unusual and characteristic for diamonds treated with such high irradiation doses. Certain spectral features such as the 644/649 nm, the 724/734/738 nm, the 920 nm and the 967 nm absorptions were only detected in the neutron-irradiated diamonds while others such as the 6165 cm− 1 and the 805 nm absorptions were only found in the spectra of the electron-irradiated stones.In addition to these treatment experiments some neutron-irradiated very dark green (appearing black) diamonds were heated from 300 to 1100 °C in increments of 50 °C to get a precise idea of the temperature at which color changes occur and the various absorption peaks form. All diamonds turned yellowish to orangy brown after annealing above 700 °C and most of them exhibited unusually strong H1b and/or H1c absorptions after annealing at > 900 °C.