Firing electrons at the nucleus

[DrBloke]

Why can you fire neutrons or alpha particles at the nucleus and see interesting nuclear effects but you can't fire electrons at the nucleus? Or can you? I would guess not, otherwise electrons would collapse into the nucleus in every day life. I've heard that doesn't happen because it would violate Heisenberg's Uncertainty Principle. If I accept that I can't see why HUP shouldn't forbid a neutron or alpha particle being fired at the nucleus. Is it to do with electrons being leptons?

 

[Drakkith]

They do this in Deep Inelastic Scattering. That is how they found evidense that Protons and Neutrons are made up of quarks. Look it up on wikipedia for more info.

 

[DrBloke]

Thanks Drakkith.

 

[Bill_K]

DrBloke, One of the first topics covered in most books on nuclear physics is, "How big is the nucleus?" And, "How does its size increase as the atomic number increases?" An important result is that the nuclear radius grows as A^1/3, indicating that the nucleons are packed together at a relatively constant distance apart. Nuclear size measurements like this were done by scattering electrons off the nucleus, with energies in the range of 100-200 MeV. Electrons don't see the neutrons, of course, but they reveal the distribution of the protons and the two types of particles have very similar distributions.

 

[Drakkith]

I thought electrons can "collide" with quarks inside a neutron and be deflected and such.

 

[Bill_K]

What you can see depends on the energy. Electrons with 100-200 MeV with a wavelength greater than a fermi see only a blurry picture of the charge distribution of the nucleus as as whole. Electrons in the GeV range resolve the charge distribution that exists inside individual protons and neutrons. (structure function or form factor). Beyond 10 GeV you start to see and interact with the individual quarks and gluons.

Even for low energies the elastic scattering will be accompanied by inelastic scattering (e.g. creating a pion costs only 135 MeV. Creating a photon costs even less than that!), so you need to filter the data to select the elastic events, those have small or zero missing mass.

 

[Drakkith]

What you can see depends on the energy. Electrons with 100-200 MeV with a wavelength greater than a fermi see only a blurry picture of the charge distribution of the nucleus as as whole. Electrons in the GeV range resolve the charge distribution that exists inside individual protons and neutrons. (structure function or form factor). Beyond 10 GeV you start to see and interact with the individual quarks and gluons.

Even for low energies the elastic scattering will be accompanied by inelastic scattering (e.g. creating a pion costs only 135 MeV. Creating a photon costs even less than that!), so you need to filter the data to select the elastic events, those have small or zero missing mass.

Ah, I see. Thanks.