Radiation

Some materials give off radiation, measured in Ru (dose rate). Uranium is the first.

What you take

Everything radioactive you carry counts in full: ingots, ore, parts, a weapon with a uranium part in it. A radioactive block or a dropped item within five blocks counts for less the farther it is (at one block, half). Add it all up and that is the rate you stand in.

Your body clears a little each second. A rate under 0.2 Ru does nothing however long you stand in it; over it the dose builds. Armour shields by how dense it is, read from the material: lead does best, iron nearly as well. Wear less and you take more; wear uranium and you are the source.

What it does

The dose you carry (kept between sessions, lost on death) makes you ill in three steps: hunger, then weakness and mining fatigue, then the wither. Nothing is locked and nothing is instant: it is a bill that grows the longer you stay, and drops once you leave. A Geiger Counter tells you the rate before the body does.

Creative players take nothing.

Not yet

A chest or a lead box does not shield what is inside it, and a wall does not shield you from a block on the other side of it: only distance and armour do. Carry sources in your hands and keep them out of your pockets.