Radon

Radon is a highly radioactive and deadly gas with very specific formation situations. Radon comes in 3-tiers of hazard. As a gas, it is invisible and cannot be physically interacted with, but will give high amounts of radiation when passed through and breathed in.

Production
Radon gas can be released or formed when Uranium is mined, nuclear waste blocks exist, or when Ancient Scrap Metal receives a block update. It cannot be acquired into inventory outside of creative mode.

Uses
Radon has no uses outside poisoning all life exposed to it with large doses of radiation.

Dense and Tomb tier radiation can bypass gas masks and are especially deadly, so you can kill players wearing Euphemium armor with it.

Tiers
Radon is not produced equally, it comes in three tiers and each one is more deadly than the last.

Radon Gas (Tier 1)
Simplest form, fairly radioactive, but can be blocked with gas masks fine enough.

Dense Radon Gas (Tier 2)
Advanced form, formed from nuclear waste blocks or dirty explosions. Highly radioactive, bypasses gas masks with no issue.

Tomb Gas (Tier 3)
Extremely dangerous, formed only by Ancient Scrap Metal receiving block updates. And to think you thought dense Radon was dangerous enough.

Trivia

 * It is fairly easy to kill a player in Euphemium armor in theory using the later tiers of Radon gas, since it bypasses gas masks and radiation resistance provided by armor does not apply to gases inhaled.