Does radioactive stuff go away from like a nuclear bomb after a long time

As far as I know radioactive stuff doesn't become less radioactive over time. If an rbmk explodes picking up the debris will make the area less radioactive but the items themselves don't become less radioactive.

The radiation from the nuclear explosion is relatively short lived, any residual radiation is caused by the sellafite blocks that spawn. Sellafite will decay after some time, turning into non-radioactive slaked sellafite, so after a while the crater should become non-radioactive.

Alright thanks