noun
- A radioactive metallic chemical element with atomic number 89, used in nuclear research and as a source of alpha particles.
Usage: chemistry; physics
Examples
- Actinium is a rare radioactive element found in uranium ores.
- Scientists use actinium-227 in medical and industrial applications.
- The discovery of actinium in 1899 expanded the periodic table.
- Actinium glows in the dark due to its radioactivity.
- Nuclear researchers study actinium's decay properties.