Talk:Klein–Nishina formula

The text states that:

"The value dσ/dΩ is the probability that a photon will scatter into the solid angle defined by dΩ = 2πsinθdθ."

A differential cross section is not a probability. It is an equivalent area for a target particle to scatter an incident particle into a given solid angle. As such, it is proportional to the probability that one of the incoming photons scatters into the solid angle.

Wigcp 03:45, 25 July 2007 (UTC)[reply]

Units

I think the formula given is valid only in Lorentz-Heaviside units. It would have various factors of $4\pi$ and $\epsilon _{0}$ floating around if it were written in SI or Gaussian units. I haven't made the changes myself as I'm not sure of my facts: I came to this article to find out for sure! Thanks. Matt (talk) 16:32, 4 January 2010 (UTC)[reply]

As written, it's correct: all the weird unit conversion factors are buried inside the

\alpha

. The definition of the fine structure constant in terms of other constants depends on the unit system, but in any unit system it ends up as the unitless number about 1/137. Spatrick99 (talk) 21:31, 9 December 2010 (UTC)[reply]

Reference to the Compton scattering formula

The P(E,theta) is basically the compton scattering formula. I think this should be mentioned. Otherwise it is not clear where the expression for P is coming from. — Preceding unsigned comment added by 140.181.68.37 (talk) 09:27, 2 August 2013 (UTC)[reply]

To be honest, the whole wikipedia page should be re-written for this, or at least the equations, because the notation is more complicated than it needs to be. I do not see any sense for example why the letter P is used, it is not a standard practice anywhere at all, the "reduced" Compton wave length is NEVER indicated by the letter r, it should be a lambda (with a subscript of your choice as long as it's reasonably sensible). Indicating that P is a function of theta and E_gamma inside the Klein-Nishina formula itself, is again completely unnecessary, it just makes the equation look more cluttered for no good reason, furthermore it is not overly clear what P means in the formula, if you are not yet familiar with it, it would be much better to stick with E, E' and Eo, just like everywhere else. — Preceding unsigned comment added by 94.194.205.197 (talk) 03:03, 9 May 2014 (UTC)[reply]

possible misprint

@Socob: since you have added the total cross section please check if the first term has eps^2 or eps^3 at the denominator. thanks 151.29.39.54 (talk) 23:42, 18 November 2024 (UTC)[reply]

The cross section as written should be correct, and matches that given in Gamma ray cross section#Compton scattering cross section. The ϵ² vs. ϵ³ is simply a difference in distributing a factor of ϵ between the two factors (the one before the parentheses, and the one in parentheses). Socob (talk) 21:14, 26 November 2024 (UTC)[reply]

Also, I do not understand the exact meaning of

On the low-energy limit there is no energy dependence,

does it mean that do not diverge? that the value in 0 is a constant? As a matter of fact, the quantity behaves as (1-2*x). — Preceding unsigned comment added by 151.29.39.54 (talk) 06:34, 19 November 2024 (UTC)[reply]

I didn’t add this sentence, but of course it depends on to which order the approximation is done. Yes, to first order in x, the dependence is (1 - 2x) for x ≪ 1, but obviously this dependence is only valid for small x, and a constant is a very good approximation. Socob (talk) 21:21, 26 November 2024 (UTC)[reply]