Promethium is a chemical element with the symbol Pm and atomic number 61. It is a rare earth element that is silvery white in color and it fairly soft. Promethium does not exist freely in nature because it is highly radioactive and decays quickly. It is mainly produced in nuclear reactors.

Promethium is used in many applications, including portable X-ray machines. It can also be used in nuclear batteries and as a source of energy for satellites. In addition, it has potential uses in medicine, such as in cancer treatment.