Lanthanide Series: A group of elements from lanthanum (La) to lutetium (Lu), often known as rare earth metals, characterized by filling of the 4f electron orbital.
Transuranium Elements: Elements with atomic numbers greater than uranium (92), all of which are synthetic and include some members of the actinide series.
Radioactivity: The process by which unstable atomic nuclei lose energy by emitting radiation; a common property among many actinides.