I think it would be cool, and realistic, if water source blocks acted as radiation shielding since water is surprisingly dense and makes for good gamma and neutron absorbers IRL, also when it does that it emits cherenkov radiation so water source blocks exposed to radiation should also emit light.
Also personally (assuming it doesn't already work this way), it would be cool if all blocks, depending on hardness, blocked a certain amount of radiation based on line of sight to a radioactive block.

"Also personally (assuming it doesn't already work this way), it would be cool if all blocks, depending on hardness, blocked a certain amount of radiation based on line of sight to a radioactive block."
This exists for high rad blocks like corium etc when they give non-chunkrads.

Thats a nice idea