·A radioactive metal.

·Most promethium is used only in research. A little promethium is used in specialised atomic batteries. These are roughly the size of a drawing pin and are used for pacemakers, guided missiles and radios. The radioactive decay of promethium is used to make a phosphor give off light and this light is converted into electricity by a solar cell.

·Promethium can also be used as a source of x-rays and radioactivity in measuring instruments.