Primary Uses
Betavoltaic nuclear batteries, Industrial thickness gauges, Radioluminescent light sources
Short Description
Promethium is the only rare earth element with no stable isotopes - every form is radioactive. The longest-lived isotope (Pm-145) has a half-life of just 17.7 years, meaning virtually none survives from Earth's formation. At any given moment, an estimated 500-600g exists across the entire planet as a trace product of spontaneous uranium fission. It is never mined. Commercial Pm-147 is produced either as a nuclear reactor fission byproduct (separated from spent fuel rods) or by neutron irradiation of Nd-146 in a reactor. Its primary application is betavoltaics - converting beta radiation directly into electricity for long-life atomic batteries once used in cardiac pacemakers (pre-1970s, before lithium cells) and still used in precision instruments, guided systems, and remote sensors. It is also used in industrial beta-ray thickness gauges for measuring thin films and materials, and historically in radioluminescent paint for military instrument dials before tritium alternatives became standard.