The range of Klein-Nishina formula

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Discussion Overview

The discussion revolves around the Klein-Nishina formula, particularly its applicability in photon-electron interactions, especially at various energy levels. Participants explore its limitations, experimental validation, and theoretical implications in different contexts, including gamma rays and lower energy photons.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the range of the Klein-Nishina formula, asking if it works at all frequencies or if it breaks down at some point.
  • Another participant notes that the formula is primarily applicable for gamma rays, where electron binding energy can be neglected, suggesting that other effects dominate at lower energies like X-rays.
  • A participant inquires about the possibility of measuring the recoil angle and speed of the electron, questioning whether these values are derived from the formula or can be directly observed.
  • There is a discussion about the implications of high-energy gamma rays, with one participant speculating on the behavior of photons and electrons when the energy of the gamma ray is significantly greater than the electron's rest mass.
  • One participant shares links to resources that may provide additional information regarding the Klein-Nishina formula and its applications.
  • Another participant expresses difficulty in understanding the provided resources but seeks clarification on the feasibility of measuring the recoil angle and momentum/energy of the electron.
  • It is mentioned that the Klein-Nishina formula provides a probability distribution for the outgoing photon angle relative to the incoming direction.

Areas of Agreement / Disagreement

Participants acknowledge that the Klein-Nishina formula has a limited range of validity, particularly for lower energy interactions. However, there is no consensus on the specifics of its limitations or the feasibility of measuring certain parameters related to electron recoil.

Contextual Notes

Some participants express uncertainty regarding the experimental verification of theoretical predictions related to electron recoil and the accuracy of the Klein-Nishina formula under various conditions.

Who May Find This Useful

This discussion may be useful for those interested in photon-electron interactions, the limitations of theoretical models in physics, and experimental physics related to scattering phenomena.

bobie
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I found a nice applet: http://www.kcvs.ca/site/projects/physics.html
to study that formula, but it has a limited range.
Do you know of a better app or of a site where I can get results of real experiments?,
can someone tell me:

- does it work at all frequencies, or does it break down somewhere?
- is there a threshold over which the photon cannot be scattered at 180°?
- as the electron is inside a metal, can its recoil angle and speed really be observed and measured, or is it derived from the formula?
- if the energy is low , around 5.11 eV (1.2*1015 hv) what is roughly the speed of the electron ? I mean: does it get energy only from the photon (in the range of 0.0001 eV)?

Thanks for your help
 
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Klein-Nishina is the formula for interaction between photons and free electrons. Its application is mainly for gamma rays where the electron binding energy can be ignored. At lower energies (X-rays etc.) other effects predominate.
 
mathman said:
Klein-Nishina is the formula for interaction between photons and free electrons. Its application is mainly for gamma rays where the electron binding energy can be ignored. At lower energies (X-rays etc.) other effects predominate.
Thanks, mathman,
so it has a limited range of validity. Has the angle of recoil and speed of the free electron ever been verified?, what is the accuracy of the theoretical formula?
What happens if the energy of the gamma ray is thousand times the rest mass: the photon should
continue in its direction pushing the electron like a cannonball a pingpong ball, but the photon is always faster, then should be reflected. Can an electron act like a wall to a photon , say, 10^30 hv?
 
mathman said:
http://physics.indiana.edu/~shylee/p672/EM_scattering_1.pdf
.

thanks, mathman, your link is very useful, though somewhat difficult for me:I'll try to digest it, but at a first examination it seems that there is nochance of measuring the recoil angle and the momentum/energy of the electron. Is that correct?
 
The Klein-Nishina formula gives the probability distribution of the outgoing photon angle with respect to the incoming direction.
 

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