It would be nice if you can add a creative Radiation Scrubber/Provider that can remove a configurable amount or keep the radiation in one chunk at a desirable level like if you want to have a chunk with a radiation level at 100mRAD, you can configure the block so it can irradiate the chunk up to 100mRAD and stop there.

I should have mentioned this at the time, but as QuantumTraverse says, this can be done with a command block in creative mode.

One can set chunk radiation through commands, so one can just use a command block to do this.