Say that a wizard had to walk through nuclear fallout for whatever reason. Is there any sort of spell that would protect against nuclear radiation? It seems that most of the protection spells (e.g. protego) protect against physical attacks.
When travelling through nuclear fallout, there are two things you want to achieve to stay safe:
- Do not breathe the dust
- Do not get (too) irradiated
Bubble-Head Charm gives you a bubble of fresh air, uncontaminated by the radioactive dust. It works out of water as well:
It causes a protective bubble to form about the caster's head, described to look like upside-down fish bowls; this bubble may allow for underwater exploration or to avoid nasty smells, although wizards with bad breath have reported problems after the first thirty minutes
As for the Cloak of Invisibility, it appears to let the majority of light pass right through it without getting absorbed by the wearer. Well, ionizing radiation — in this case gamma radiation — is just that: light... photons to be more exact. (*) They just have a higher frequency than normal visible light. The cloak will make these nasty gamma photons pass right through you without interacting with your cells.
Visible light and gamma radiation are both on the Electromagnetic Spectrum
And with these you have fairly good protection against nuclear fallout. It is not perfect; you will want a good scrub-down to get the radioactive dust off of your skin, hair and clothes once you are clear of the fallout. But it will help keep the absorbed radiation dose down in such a way that a wizard can endure fallout much better than unprotected muggles. Too much will be too much though... a plain old physical dosimeter is advisable to carry.
(*) Alpha radiation is stopped by clothes and the (dead) outermost layer of skin and is not a problem as long as you do not breathe alpha-radiating particles. Beta radiation is electrons and is a bit more of a bother but is rarely a problem with fallout.
Not that we know of, but there's no reason it wouldn't be possible.
There's no spell mentioned in any level of canon, from the books to even the most questionable of sources. This is simply because the subject of nuclear radiation never comes up in even the slightest capacity, nor is there any reason for it to.
However, there's nothing that implies that there can't be a spell to protect against nuclear radiation, or even that there mightn't be one already. There theoretically could be, and if there isn't, a wizard who knows about nuclear radiation could create one. Spells aren't limited to protecting against physical things. Spells themselves are a type of energy, and there are spells like Protego that protect against other spells. In addition, there are spells, like the ones cast around Hogwarts, that protect entire areas against spells. It should be possible to do the same thing with nuclear radiation.
Unfortunately... we don't know for certain. At best we have Shield charms.
When you think of a spell that protects against something, naturally Protego comes to mind. However there are no instances where Muggles use an atomic bomb or like kind to destroy Wizards, and therefore we can't be 100% sure a shield spell would work.
There may be other more potent kinds of shield spells though, such as the one Voldemort uses in OotP:
Voldemort was forced to conjure a shining silver shield out of thin air to deflect it.
Of course, we don't know whether the shield would hold against a nuclear warhead or radiation. All speculation.
Canonically, no such spell is mentioned. However, the Department of Mysteries studies enigmas such as Space, Time, Death, Love and Thought, most of which are far more abstract and highly difficult to analyze, compared to Nuclear Radiation, which is purely physical. So, you may safely assume that a civilization that is capable of mass producing Time Turners would have created a spell to provide protection against nuclear radiation, particularly since the Statute of Secrecy forces them to constantly be vigilant against nuclear or any other threats from Muggles.