Recent content by physics_fun

Hey, I'm working on a problem about the atomic form factor. I found that the atomic form factor of an fcc lattice of Buckyballs (C60 atoms) looks like f~(sin(Gr))/G multiplied bij some constants. The question is now to explain from this atomic form factor why the (2,0,0) X-ray diffraction...

:blushing: You're right, I didn't think of that!

I think there is still a mistake, because 4 \pi \nabla_a j^a = \nabla_{[a} \nabla_{b]} F^{ab} = - \frac{1}{2} ( R_{abc}{}^{a} F^{cb} + R_{abc}{}^{b} F^{ac} ) = \frac{1}{2} (R_{bc} F^{cb} - R_{ac} F^{ac} ) = \frac{1}{2} (R_{bc} F^{cb} + R_{ac} F^{ca} ) so they don't cancel. Is there a...

Thanks! I've spent almost the whole day on it, because I didn't know which way to go... Are you allowed to take only the asymmetric part of the covariant derivatives \nabla_{[a} \nabla_{b]} F^{ab} because the symmetric part gives zero in combination with the anti symmetric F tensor?

For the case of ordinary erivatives that is true, because these derivatives commute. But I am looking for the proof in de case of covariant derivatives, and these don't necessarily commute...:(

I'm reading some texts on general relativity and I am wondering how one can mathematically proof that the covariant derivative (wrt mu) of the four-vector j^mu equals zero. I know that the covarient derivative (wrt nu) of F^mu^nu equals the four-current times some costant and that you should...

Maybe I didn't formulate it very clear, but what I mean is this: http://www.shef.ac.uk/physics/teaching/phy303/303soltn1.html#sols2 (2nd solution) So in this calculation it is about 64% of the time the case. But I don't know why the deuteron doesn't dissociate...

You can calculate that the proton and neutron in a deuteron spend quite some time so far away from each other, that they are outside each others force range. Why doesn't the deuteron break up? Is it because of the binding energy?

Thanks!:smile:

I'm confused about how parities 'add up'. (I'm using the shell model of a nucleus) If you have e.g.a neutron in a d state (so l=2) and one in a p state (l=1), what is the parity of the total system? Do you have to multiply (+1*-1=-1?) or add the l values or something completely different?

It's completely clear to me now! Thank you very much for your help!:smile::smile::smile:

small angle approximation:wink:

About the second: is it true that (threevectors:) if p2=0, p1=p3+p4 so (p1)^2=(p3)^2+(p4)^2+2(p3)(p4) now (p3)(p4)=0, so (p1)^2=(p3)^2+(p4)^2, and this can only be true if p4=0 or p3=0?

I'm understanding this one:cool:!

Ok, I think I'm getting it now: E1, E2, E3 are the rest-energies, p1, p3, p4 the three vectors (p2 is defined 0)