I was watching a video about quarks and they said that they made an experiment where they fired electrons into protons and saw how they bounced.
All this makes my head hurt like.. how do they do that? How to they see what happens when the electrons are fired? How so they see where they bounce?
You can’t observe all this with microscopes right? So how does it all work?
In: Chemistry
Particle accelerators.
Large particle accelerators like the Large Hadron Collider in Switzerland or the Relativistic Heavy Ion Collider in New York all have one goal — to smash individual subatomic particles together and see what happens.
Ever heard of a rail gun? Instead of a traditional bullet which operates on the principle of expanding gasses in a confined space (i.e. the gun barrel), a rail gun uses powerful magnets with precise timing to accelerate a projectile down a channel. The result is a bullet that exits the gun with a much higher velocity than could ever be achieved with gunpowder, with a much higher level of accuracy.
Particle accelerators do the same thing, but with atoms. Using powerful magnets, they accelerate two particles in opposite directions through a giant ring, then smash them together once they’ve hit a good fraction of the speed of light. The chamber where they collide is lined with all kinds of sensors and other equipment to measure the reactions.
You cannot observe things as small as atoms directly with a microscope. All we can do is theorize what might happen in these collisions based on what we think we know about them, and then design sensors to measure the effects to see how right or wrong we were.
First you need to create a beam of electrons. Basically you can do this by just heating up a piece of metal and use a high electrical voltage (multiple kilovolt or higher on it), to accelerate them.
Then you direct this beam onto a target. This target is what you want to investigate. The electrons of your beam will interact somehow with your target and it might change the direction of electrons in your beam, it might change the energy of your electrons, create new electrons, create light, etc.
These changes you can measure with specialized detectors. You cannot “see” electrons with them directly, but basically you get an electrical signal which is somewhat related to the quantities you can measure.
Or if you have high enough energies you can visualize the electrons by directing it on a phosphorous screen, where the electrons create light, allowing you to see in which directions the electrons move.
You can use all of this information, to get information about crystal structure of a material, what elements it contain, what electronic properties it has and more. You can even use an electron beam to make high resolution pictures of the samples (which is then called electron microscopy).
You don’t watch with a microscope, but you do have detectors.
One such detector is a phosphor screen, which is basically just a sheet of glass that’s been treated with chemicals that emit light when struck by certain particles. Electrons are one such particle.
So the first thing that you do is figure out a way to emit a beam of electrons. This actually isn’t that hard to do – you can look up instructions for making a basic beam online. Once you have your beam, you point it at your phosphor screen. When it’s struck by your beam, it will light up. Shine it directly at the screen, and you’ll have a bright spot. Move it around, and you’ll have a moving bright spot. This, by the way, is effectively how CRT TVs worked.
You’ve now established your beam, and you’ve established that you have a detector to tell where your beam is. Now you can point your beam at a target and see what happens. You know that it will behave in certain ways if nothing gets in the way. So if you see that the beam reacts differently, you can reasonably interpret that difference as the effect of your target.
On top of that, you also have some theories about what it would look like if a beam of electrons struck a certain target. The math is somewhat complicated, but you can model what an electron should do when it strikes a proton, and extrapolate that to what you would expect to see on your phosphor screen – maybe a dark spot where it should be light, maybe the light spot showing up somewhere other than where you’re pointing the beam. Whatever it is, you can make predictions, and you can then test those predictions with your physical apparatus.
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