CombatWombat

Mmm this is a good interpretation. You get radiation poisoning and only die later. If for whatever reason, this item appeared at my table and we needed to adjudicate this, I would totally accept this reading.

I’m not aware of any nonmagical items that require attunement, so I think that point also stands. If you were to use such an item without attunement and it were magic, you would do the bludgeoning damage and not the radiant damage.

I thought death broke attunement, and you had to reattune after being resurrected?

As a boring killjoy D&D rules lawyer, I might point out that this will definitely lead to “them” winning, since you are killed when you attune, and therefore can never deal the 1d8 bludgeoning + 30d12 radiant damage.