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.