If neutrinos are so small, why can’t they be used to shoot at, say a proton or neutron and then hit a background so as to take a picture of what the proton really looks like? They always say you can’t picture a proton because it is so small, but a photon is smaller already, so why can’t even that be used? And if not, then use neutrinos.
my GUESS is that the picture you get would be too small.
i also guess that i don’t know.
There are non-trivial difficulties in generating, collimating, and detecting neutrinos. Additionally, neutrinos have a very small (or perhaps zero; I’m not up on the latest thinking on this) rest mass, but that says nothing as to their physical dimensions; indeed, if I’m not making an egregious error here[sup]1[/sup], their DeBroglie wavelength ought, by virtue of that fact, to be very large. We could pump up their energy of translation (assuming that we could generate them reliably) to decrease their wavelength, but then to have one collide with a proton would knock it for six (Uncertainty Principle).
[sup]1[/sup][sub]Always a possibility; get the resident penguinist.[/sub]
As usual, I’ll just give you an overview, in the time it takes for Chronos or someone like him to show up and fill in the details.
There are two problems with your ideas. First, photons aren’t necessarily smaller than protons. Second, neutrinos are hard to detect, so they won’t ‘expose the film’. They’ll pass right through it.
When attempting to get information about something by shooting wavicles at it, the wavelength is important. In order to ‘see’ an object, the wavelength of the radiation used must be significantly smaller than the object. In one of my old physics books, they used water waves as an illustration of this. A battleship standing in wavy water influences the waves, so that the waves that pass it are altered by it’s presence. In essence, the ship casts a sort of shadow in the wave pattern. However, reeds growing in the same water do not alter the waves at all, because they are smaller than the wavelength.
For taking images, visible light has a small enough wavelength to see most any object, down to large molecules. To go smaller, they generally use an electron beam, which has an even smaller wavelength.
It isn’t really even proper to speak of photons as being small, since they are essentially smeared out across they’re wavelength. So, they only appear small when the wavelength is small. In order for the wavelength to be much smaller than a proton, the energy has to be very high. Now, what you’re dealing with is a gamma ray of significant power, and it tends to knock the proton around a lot. You know, ‘the act of observing disturbs the observed.’ You can’t get a good picture that way.
I could probably ramble on, but I’ll stop now. Please point out what here needs clarification, and someone will give more details.
Since I know the difference between ‘they’re’, ‘their’, and ‘there’, why don’t my typing fingers have that same knowledge? Arggh.
Very enlightening replies which I understand for a change. Evidently I must throw out my NEUTRINORAMA, the device I was working on to photograph protons, neutrons, and so forth.
Back to the drawing board. I’m still upset by the fact that physics books leave out PICTURES of little particles, which I want to think of as little spheres…
don, if you haven’t read it already, you must look at this column. It is the example I always point to when I show someone unfamiliar with Cecil’s work how much fun this guy is.
The story of Schroedinger’s cat (an epic poem)
Saltire, I hadn’t seen that before. That’s just incredibly excellent 
'Course, I already knew how much fun Unca Cece could be.
LL
A neutrino should have the same wavelength as a photon of the same energy (or approximately the same, if they have slight mass: The jury’s still out on that one). In principle, you could use them for imaging (heck, in principle you could use Beanie Babies shot out of a cannon), but there’s two big problems. First off, they’re nearly inpossible to detect; even with the most powerful sources we have, you still only get single-digit event rates. Secondly and perhaps more importantly, aside from insanely strong gravitational fields, there’s no known way to focus them, so any “image” you could get of a proton would be the size of the proton itself. Plus, there’s no real advantage to using them rather than light, unless you’re trying to look at something on the other side of a couple of lightyears of lead shielding.
There is no point in ‘looking’ at a proton. it would be a boring little sphere. It would be impossible, for instance, to find out what ‘colour’ it was.