Lanthanides:A group of 15 metallic elements from lanthanum (La) to lutetium (Lu) in the periodic table, often found together with actinides in f-block chemistry.
Radioactivity: The spontaneous emission of particles or radiation from unstable atomic nuclei, a characteristic feature of all actinide elements.
Transuranium Elements: Elements with atomic numbers greater than that of uranium (92), many of which belong to the actinide series and are synthesized artificially.