Radium-226

Radium-226 is a mildly radioactive decay element from Uranium and Plutonium.

Production
Mainly produced from the processing of Uranium and Thorium ores.

It can be made by bombarding Lead with Carbon in a Cyclotron.

Uses
Safe and consistent Ra226Be Neutron Sources for RBMK and Research Reactors.

Weak RTG pellets. They provide 3 power per tick. If RTG decay is enabled, each will have a lifespan of 11,520,000,000 ticks, computing to ~18 IRL year, with a stated in-game lifespan of 2,400 years (assuming a 100 day year). They decay to Lead pellets. This also means it will make 34,560,000,000 power in total over that time.

A joke consumable item, Radium Coffee.

It has a planned use for glow in the dark paint.

Trivia

 * Radium was actually used for glowing paint until the hazards were became more known to the public.
 * If you have Radium-based paint in your possession IRL, deal with it with caution or simply do not expose yourself to it.