It was named after the titan who stole fire from the gods. Promethium is the only lanthanide with zero stable isotopes. Every single atom decays. Nature created this element but refused to keep it — on Earth, it is virtually absent.
Scientists first isolated promethium in 1945 from uranium fission debris. It glows in the dark, powers tiny atomic batteries, and helps measure the thickness of metal sheets. But its radioactivity demands extreme caution. This is an element that humans literally had to create themselves — just as Prometheus created fire.
Promethium is produced exclusively in nuclear reactors from the fission of uranium-235. Annual global production amounts to just a few hundred grams. The isotope Pm-147 has a half-life of 2.62 years and emits soft beta particles.
Its practical uses are limited but unique. Industry relies on Pm-147 for thickness gauges that measure paper, plastic, and metal foil. Atomic batteries based on promethium once powered space probes and cardiac pacemakers. Historically, Pm-147 was mixed into self-luminous paints for watch dials and instrument panels.
Promethium-147 is a radioactive beta emitter with a half-life of 2.62 years. Beta particles cannot penetrate skin and are stopped by clothing. However, if inhaled or ingested, promethium accumulates in bones — much like calcium — and irradiates bone marrow from within, raising the risk of leukemia. Working with promethium requires sealed gloveboxes, plexiglass shielding, and continuous radiation monitoring. All promethium compounds are classified as radioactive waste.
Scientists hunted element 61 for over 40 years. Bohuslav Brauner predicted its existence in 1902, but only in 1945 did Marinsky and Glendenin isolate it from uranium fission products at Oak Ridge.
Even the most stable isotope, Pm-145, survives only 17.7 years. If promethium had formed with Earth 4.5 billion years ago, it would have vanished within the first few millennia. That is why it barely exists in nature.
A Pm-147 atomic battery the size of a coin could power a cardiac pacemaker for years. Beta particles heat a thermoelement that converts warmth into electricity — with no moving parts whatsoever.
In the 1960s, promethium was added to watch dial paint. A mixture of Pm-147 with ZnS phosphor produced a blue-green glow for years on end — no batteries or charging needed.
Promethium is among the most expensive elements on the planet. Its price exceeds $1,000 per gram. The world produces only a few hundred grams per year — less than the weight of an apple.
In industry, Pm-147 measures the thickness of paper, plastic, and metal foils. A stream of beta particles passes through the material, and a detector on the other side determines thickness down to the micrometer.
| Isotope | Mass (u) | Abundance | Half-life | Decay |
|---|---|---|---|---|
145Pm☢ | 144.912749 | synthetic | 17.7 years | EC |
147Pm☢ | 146.915139 | synthetic | 2.6234 years | β− |
Uranium fission products