A metal that glows blue in total darkness. Not from electricity — from its own radioactivity. This is actinium, the first element in the actinide series. It is so rare that only a few tons exist in the entire Earth's crust. Marie Curie's colleague discovered it in 1899.
Actinium emits powerful alpha particles. That very property made it a beacon of hope in cancer treatment. The isotope actinium-225 kills tumor cells with surgical precision, leaving healthy tissue untouched. It is one of the rarest and most valuable medical isotopes in the world.
In nature, actinium shows up in uranium ore. But barely — just 150 micrograms per ton. So for research and medicine, scientists produce it artificially by irradiating radium-226 in nuclear reactors.
The most promising use is targeted alpha therapy for cancer. Alpha particles from actinium-225 travel only 0.1 mm — enough to destroy a tumor cell but too short to damage its neighbors. Clinical trials are already testing this approach against prostate cancer and leukemia.
Actinium is extremely radioactive. It emits alpha, beta, and gamma radiation simultaneously. If it enters the body, it accumulates in bones and liver, destroying cells from within. Handling requires sealed gloveboxes with lead shielding. Even microgram quantities demand special ventilation and remote manipulators. Direct skin contact is strictly forbidden.
Actinium glows blue in the dark. It is not phosphorescence — its radioactivity ionizes air molecules, which then emit visible light.
Andre-Louis Debierne discovered actinium in 1899 in Paris. He worked in Marie and Pierre Curie's laboratory, studying leftover residues from uranium pitchblende.
The name 'actinium' comes from the Greek word 'aktinos,' meaning ray. Scientists named it for the intense radiation they detected immediately after its discovery.
Actinium-225 is called oncology's 'silver bullet.' Its alpha particles travel only 0.1 mm and destroy cancer cells while barely touching healthy ones.
The entire Earth's crust contains only a few tons of actinium. It is millions of times rarer than gold — one of the scarcest natural elements.
The most stable isotope, actinium-227, has a half-life of 21.8 years. That means half of any sample disappears in just over two decades.
| Isotope | Mass (u) | Abundance | Half-life | Decay |
|---|---|---|---|---|
225Ac☢ | 225.023230 | synthetic | 10.0 days | α |
227Ac☢ | 227.027752 | synthetic | 21.772 years | β−/α |
Separation from pitchblende