Promethium is a rare, radioactive element with the symbol Pm and atomic number 61. It belongs to the lanthanide series of the periodic table and is known for its silvery-white appearance. Promethium is primarily produced synthetically, as it does not occur naturally in significant amounts on Earth. It is used in some specialized applications, such as in luminous paint and atomic batteries. Due to its radioactivity, promethium must be handled with care. It has a relatively short half-life, which means it decays quickly. The most stable isotope, Pm-145, has a half-life of about 17.7 years. Promethium's unique properties make it valuable in research and certain industrial applications.