What Would Be a Scientifically Accurate Weakness for a Radiation-Based Superhero?

I'm trying to write a comic book script about a superhero with radiation-based superpowers, specifically generation of atomic radiation, but I want to keep it somewhat grounded in reality, so I need to know as much about atomic radiation as possible. Mainly I'm trying to figure out if there is anything that can mess with radiation that could neutralize the hero's powers, or at the very least make things a whole lot difficult for him. At the moment, I've decided that electricity and electrical fields leave his powers a bit on the fritz, based on some research I did, but after even further research I'm starting to think that might be inaccurate. Any ideas?

Lead is used to absorb radiation. Pretty sure they line MRI's in hospitals with it to suck up some of the radioactivity.

@strider1992: Okay, that's a start...

Magnets or artificial magnetospheres can redirect or slowdown radiation.

Vitamin c and melatonin.

Prolonged exposure can cause cellular degeneration and mutations in mitosis.

If he or she uses their power roo much they could almost kill themselves.

It might get wonky to explain but you could have some other type of radiation that his or her radiation cancels out with.

Think of it like negative propogation, and destructive convergence.

Lead would make sense but that is too common.

Time. While it could take awhile, radiation does decrease over time (radioactive decay, half-life and such).

If your comic is going to be a one-shot: I'd say a weakness that your hero could have is that the powers are slowly weakening after each use. It could force your character to further hone his skills and wits as a crime-fighter after this weakness is discovered as well as lead to a theme that even a superhero has to either hang up the cape and retire eventually or die past his prime in the heat of battle.

You could have all the powers you want and beat every opponent you come up against but in the end, time will always beat you.

If your comic will ideally run indefinitely: A weakness I'd think might be nice is that overuse/overexertion causes your character's power to being temporarily inert and cause temporary impairment. Kinda like the Sharingan in Naruto before Kishi made it broken. Only this time the effects get worse for each new power unlocked. Your character can recharge by resting and waiting for the radiation levels to build up again (how long that takes or if it's consistent is up to you).

Again this could also force your character to hone his/her skill and focus more on controlling his powers and deciding which technique to use for certain situations instead of spamming every new trick once he learns it.

Cancer?

Lead plating can stop most ionising radiation. Radiation also has poor penetrating power through water. Depends on what kind of radiation we're talking about. Magnetic fields/Electromagnetic fields can stop Radiation...it's how the Earth prevent's the Sun from frying it, like how Mars gets fried.

This one is actually pretty good, he could have some kind of degenerative dissease, making the radiation to help him stay alive, but at the same time messing something up in his body.

@sergeant-rl3: There we go, electromagnetic fields! That's all I really needed to know! That would definitely make a better villain gimmick than lead.