astatine
/ˈæstəˌtin/
noun
- A rare, radioactive chemical element. It is the heaviest known halogen and is found in very small amounts in nature.
- The element astatine was first produced artificially in a laboratory in 1940.
- Astatine is so rare that there is less than one ounce of it in the entire Earth's crust.
- Scientists study astatine because its radioactivity might be useful in treating certain cancers.