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Actinium is a radioactive chemical element. The symbol for Actinium is Ac and the atomic number is 89. Actinium was discovered in 1899 by French chemist AndrÃ©-Louis Debierne. It was the first non-primordial radioactive element to be isolated. Actinium is amongst a group of 15 similar elements within the periodic table that make up the actinoid series. This substance was also independently...
- The navel or umbilicus.
- In Greek archaeology: A central boss, as on a shield, a bowl, etc.
- A sacred stone in the temple of Apollo at Delphi, believed by the Greeks to mark the 'navel' or exact center-point of the earth.