Recent content by Mr rabbit

Not quite. In particle physics there are two kind of processes: scattering and decays. There are two famous observables that you can calculate with QFT: cross section for the first and decay width for the second. For both you need ## | \mathcal M | ^ 2 ##, but also some kinematics of the...

I think it is correct.

Take a look at the moment of inertia: you do kg times m and you obtain kg m^2.

Thank you for your answers. I will take a look at Mattuck and Piers Coleman then!

Quantum field theory is a powerful tool to calculate observables given the amplitude of some process. I only know the application to high energy physics: you have a Lagrangian with an interaction term between some fields, and you can calculate the amplitude of some process. Once you have this...

Hmm, it's interesting. At 0.5 MeV of kinetic energy the electron will stop within the material. Remember that 0.5 MeV is the maximum kinetic energy for the electron, but the energy spectrum is continuous and the most probable energy is less. If you have a cosmic ray background with an average...

I think not. Remember that in the Debye model phonons can have any wavenumber from 0 to ##k_D = \omega _D /c##. Any state can be occupied if the temperature is high enough. Maybe you are mixing concepts: classical treatment of a chain of atoms and the Debye model, which is based on quantum...

If you want to know the mean energy of your crystal (or chain, in this case), you have to sum over all k's which are accesibles given the temperature ##T## of the chain. For each mode (##\vec{k},## p) (p is the branch) the mean energy is ## \langle E_p (k) \rangle = [ \langle n_p (k)...

Hi, the Debye model assumes a linear dispersion relation, as you say. This model "forgets" the oscillators (like coupled springs); it treats the problem as if the solid was a box with phonons inside. The mean number of phonons excited at temperature T is given by Planck's distribution...

I was thinking about electrons of 10 keV What should I do with the variable y? Another Bethe-Bloch? I am a bit lost with that. I don't know how to use it. And it's interesting for me to do the simulation by myself.

Hi, I'm trying to simulate the process of charged particles attenuation in matter (like this) by a montecarlo-metropolis algorithm in Python. I thought that I could use for the number of particles at thickness ##x## the formula ## N (x) = N_0 e^{-\mu x} ##, so the probability in this case will...

Strong and weak interactions act only at very short distances (## 10 ^ {- 15} - 10 ^ {- 17} \; m ##), so the description of these interactions is purely quantum-mechanical.

1. The declaration of the problem, all variables and data given / known Calculate the decay amplitude of ## \pi ^ 0 ## in an electron-positron pair ## \pi^0 \rightarrow e^+ e^- ##, assuming that the interaction is of the form ## \mathcal {L}_{int} = g \: \partial_{\mu} \phi \: \overline{\psi}...

I was talking to a friend about Lagrangian mechanics and this question came out. Suppose a particle under a potential ##U(r)## and whose mass is ##m=m(t)##. So the question is: the Lagrangian of the particle can be expressed by ##L = \frac{1}{2} m(t) \dot{\vec{r}} ^2 -U(r)## or I need to...

Well, this is true. Sometimes I get carried away by the intuition of classical physics. However, the interpretation is the same: both particles don't 'collide' because of the difference of the wavelengths. He told me he have been in an experiment with high energy electrons and at that conditions...