What color is commonly produced by irradiation and annealing of a type Ia diamond?

• A. Pink bodycolor.
• B. Yellow bodycolor.
• C. Blue bodycolor.
• D. Colorless.

Answer: (B)

The effect being tested is how irradiation and subsequent annealing create color centers in diamonds, and how those centers interact with the impurity content to produce color. In type Ia diamonds, nitrogen impurities are common and exist in aggregated forms. When these diamonds are irradiated, vacancies are created in the lattice; annealing then allows those vacancies to migrate and pair with the nitrogen centers. The specific vacancy–nitrogen color centers formed in this nitrogen-rich crystal tend to absorb blue light, so the diamond appears with a yellow body color. This makes yellow the typical outcome for irradiation plus annealing in type Ia diamonds. Pink coloration would come from different lattice distortions or defect structures, blue is more associated with other impurity and treatment conditions, and colorless would indicate no effective color centers formed.