Appearance and Characteristics
Harmful effects:
Promethium is harmful due to its radioactivity.
Characteristics:
Promethium is the only rare earth radioactive metal.
In the dark, its salts luminesce with a pale blue or green glow due to its high radioactivity. Isotope 147Pm, the most useful isotope, decays with energetic gamma rays.
Uses of Promethium
Promethium is useful as a beta source for thickness gauges. Promethium is also used in atomic batteries for spacecraft and guided missiles.