The V Rising Radium Alloy material is one of the new craftables that was introduced as part of the hefty Gloomrot expansion. This free update adds a new region, complete with bosses, robot enemies, and like Radium Alloy, new resources to acquire in order to construct advanced workbenches in your castle.
It's worth noting that Radium Alloy is an endgame resource. You'll need to be around level 60 in order to explore Gloomrot without dying and have a chance at beating the bosses you need to in order to craft the new resource. That said, here's how you can find Radium Alloy as loot, or make it for yourself.
