Promethium

**Definition:** A radioactive element of the rare earth family of metals. It has the atomic symbol Pm, and atomic number 61. It has been used in the construction of atomic batteries, in the preparation of self-luminous compounds, and as a beta-particle source for thickness gauges.

**Tree numbers:** - D01.268.271.720 - D01.268.558.362.875 - D01.496.749.305.720 - D01.552.550.399.875