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The Actinide series encompasses the chemical elements that lie between Actinium and Lawrencium on the periodic table with atomic numbers between 89 and 103 inclusive. They are similar in characteristics to the elements of the Lanthanide series. The actinides with the higher atomic numbers are not found in nature and have short half-lives.

The actinides are typically placed below the main body of the periodic table, in the manner of a footnote. The full-width version of the periodic table shows the position of the actinides more clearly.