Element 89 in our International Year of the Periodic Table series is actinium. The first of the actinide series of elements, actinium is radioactive, scarce, and has few uses – though has been investigated for uses in cancer treatment.

Actinium is a silvery-white metal. It’s so intensely radioactive that visible samples of it glow a pale blue colour in the dark due to its radioactivity exciting the air around it.

All isotopes of actinium are radioactive, with its most stable isotope having a half-life of around 22 years. It’s a relatively scarce element, with traces found in uranium ores. Its scarcity means it isn’t economical to extract; any actinium used in particular applications is produced in nuclear reactors.

Because of its scarcity and radioactivity, applications for actinium are minimal. Ac-225 has been investigated for radiation therapy in the treatment of certain cancers. It can also be used as a neutron source in probes that measure water quantity in soil.

Remember, you can keep track of all of the previous entries in this series on the site here, or on the Royal Society of Chemistry’s dedicated page.