Polonium-210

Polonium is a rare and extremely radioactive element only obtainable from processing neutron sources or by production in a Cyclotron. It can be turned into polonium sand, which can then be turned into a fancy, red, polonium glass. It was added in pre-release X3586. It is also pyrophoric and hot in its solid ingot form as well as its powder form, due to its extremely short half-life of 138 days.

Uses
Mainly used in the breeding reactor as fuel.

Po210Be RBMK Neutron Sources

A considerably strong RTG pellet: 50 heat. If RTG decay is enabled, each will have a lifespan of 9,936,000 ticks, computing to ~6 IRL days, with a stated in-game lifespan of 2 years and 7 days (assuming a 100 day year). They decay to Lead pellets. This also means it will make 347,760,000 power in total over that time.

A mid tier Self-Charging Battery, providing 500 HE/tick.

Transmutation into Yharonite.

Its powder form can be combined with sand to create "Polonium Sand", which then can be smelted into a novelty red "Polonium Glass". It functions the same as normal glass, is not radioactive, and is counted as red.

Production
It can only be obtained by recycling Ra226Be RBMK or Research Reactor fuel, or in a Cyclotron from Iodine or Mercury, or from nether plutonium ore centrifuging, if it is enabled.

Trivia

 * Polonium got added in pre-release X3586 along with the Breeding Reactor overhaul.
 * Polonium emits 75 RAD/s, which is probably far less than what it would actually could be considering its half-life.
 * This also means a single nugget has the same radioactivity of unenriched Plutonium or Plutonium-240 ingots.
 * It is also significantly more radioactive than Nuclear Waste or even depleted Medium Enriched Schrabidium fuel!
 * Polonium is also extremely toxic in real life, due to it being a radioactive heavy metal.