出典:Wiktionary
出典:『Wiktionary』 (2026/04/25 04:12 UTC 版)
| Chemical element |
|---|
| Ac Atomic number 89 actinium |
| Previous: ← radium (Ra) |
| Next: thorium (Th) → |
| English Wikipedia article on Actinium |
actinium (usually uncountable, plural actiniums)
| Chemical element |
|---|
| Ac Atomic number 89 actinium |
| Previous: ← radium (Ra) |
| Next: thorium (Th) → |
From Ancient Greek ἀκτίς, ἀκτῖν- (aktís, aktîn-, “ray”).
出典:Wikipedia
出典:『Wikipedia』 (2011/06/28 01:28 UTC 版)
Actinium (
/ækˈtɪniəm/ ak-tin-nee-əm) is a radioactive chemical element with the symbol Ac and atomic number 89, which was discovered in 1899. It was the first non-primordial radioactive element to be isolated. Polonium, radium and radon were observed before actinium, but they were not isolated until 1902. Actinium gave the name to the actinide series, a group of 15 similar elements between actinium and lawrencium in the periodic table.