| atom | a highly unstable radioactive element (the heaviest of the halogen series) |
|---|---|
| atom | a radioactive gaseous element formed by the disintegration of radium |
| atom | a radioactive element of the alkali-metal group discovered as a disintegration product of actinium |
| atom | an intensely radioactive metallic element that occurs in minute amounts in uranium ores |
| atom | a radioactive element of the actinide series |
| atom | a nonmetallic univalent element belonging to the halogens |
| atom | a soft silvery-white tetravalent radioactive metallic element |
| atom | a short-lived radioactive metallic element formed from uranium and disintegrating into actinium and then into lead |
| atom | a heavy toxic silvery-white radioactive metallic element |
| atom | a radioactive transuranic metallic element |
| atom | a radioactive transuranic element that is similar to uranium |
| atom | a radioactive transuranic metallic element |