Questions re Compton scattering

Click For Summary

Discussion Overview

The discussion revolves around Compton scattering, specifically addressing the implications of the scattering angle (Θ) being zero. Participants explore the nature of photon interactions with electrons at this angle, the concept of Compton forward transmission (CFT), and the challenges in measuring any associated redshift or energy changes.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant questions whether a photon at Θ = 0 misses the electron or interacts without scattering, proposing that CFT should occur, despite skepticism about the lack of redshift in such cases.
  • Another participant asserts that the probability of a photon scattering at exactly Θ = 0 is zero, indicating that the probability density does not support such a specific angle.
  • A different participant suggests that as the angular spread around zero Θ decreases, the reliability of measuring redshift also diminishes, complicating the distinction between CFT and near-zero scattering.
  • One participant emphasizes that without energy change, it is indistinguishable whether a photon was scattered or missed, while any energy loss indicates scattering has occurred.
  • Another participant notes that radiation must be measured over a range of angles rather than at Θ = 0, making it impossible to verify predictions of zero energy loss for that angle.
  • It is mentioned that accurate measurements of wavelength or energy can confirm scattering if a change is detected.
  • A participant raises the question of whether finding a change in wavelength close to Θ = 0 would imply that the Compton formula for that angle is incorrect.

Areas of Agreement / Disagreement

Participants express differing views on the implications of Θ = 0 in Compton scattering, with no consensus on whether CFT can be experimentally verified or the nature of interactions at this angle. The discussion remains unresolved regarding the interpretation of energy changes and the validity of predictions related to zero scattering angle.

Contextual Notes

Participants highlight limitations in measuring radiation at Θ = 0, emphasizing the need for a range of angles to draw conclusions about scattering events. There is also uncertainty regarding the implications of energy changes and the challenges in experimental verification.

outandbeyond2004
Messages
216
Reaction score
0
I am not sure this is the right topic for these questions. They are for the people who are familiar with Compton scattering. Let

[tex]\Theta[/tex]

be the angle that the trajectory of the scattered photon makes with the trajectory of the incident photon.

Suppose
[tex]\Theta[/tex]
is zero. Does that mean that the incident photon misses the electron (or some target charged particle) altogether or it hits the electron but does not interact with the electron at all? I can imagine the incident photon usually misses the electron, but surely there should be some hits now and then. Therefore, Compton forward transmission (CFT - not really scattering) as I shall term it should happen. The formula predicts in this case that there shall be no redshift. I find this hard to believe. It's though the cue ball goes right through the 8 ball into the pool pocket without changing the position of the 8 ball at all.

Has anyone done any detailed QFT analysis of CFT? If so, what were the results? As for experiments, I suppose it would be very hard to measure any redshift in CFT.
 
Physics news on Phys.org
The angle of scatter for Compton scattering can assume any value between 0 and 180o. The probability of it being exactly 0 (or any other angle specified in advance)is 0. In other words, the probability density has no Dirac delta function component.
 
Yes, a theoretical reason CFT is all but impossible to check cleanly. Let me see if I understand: As the angular spread around zero theta is made smaller, the redshift results become less reliable for verification purposes. I suppose one of you can put that in more technical language.

What I think I can say: Redshift does happen, though we cannot ever know for sure whether that is from CFT or from theta very close to zero.
 
I am not sure what your question means, but essentially, if there is no energy change we can't tell if is was scattered straight forward or missed - there really is no difference. If there is any energy loss, there was scatter.
 
If there is any energy loss, there was scatter.

My understanding is that we cannot measure radiation coming from theta = zero only. Rather we have to measure radiation integrated over a range of angles, zero <= |theta| < constant. Actually, a cone centered on the initial direction of the incident photon. The constant may be small but cannot be zero. Hence, we cannot know which photon in that range is a "straightforward" photon, and cannot thus verify the prediction of zero energy loss for theta = zero.

Not only would an experimentalist say that, but a quantum mechanics theorist would.

Am I correct?
 
Last edited:
The wavelength (or energy) can be measured quite accurately. Threfore if there was a change, there had to be a scatter.
 
So, if you measured close to theta = zero and found a change in wavelength = scatter, you would conclude that the Compton formula value for theta = zero is wrong?
 

Similar threads

Graduate Can scattering experiment be used to determine location and momentum of an electron?
  • · Replies 2 ·
Replies
2
Views
1K
Undergrad Annoying detail in derivation of Compton scattering
  • · Replies 1 ·
Replies
1
Views
2K
Undergrad Is the Compton scattering angle related to the incident energy?
  • · Replies 3 ·
Replies
3
Views
2K
Graduate Compton Recoil and the Electron Differential Cross Section
  • · Replies 6 ·
Replies
6
Views
4K
Undergrad Photoelectric absorption versus Compton scattering
  • · Replies 5 ·
Replies
5
Views
5K
Graduate Lay Question Regarding Compton Scattering
  • · Replies 3 ·
Replies
3
Views
2K
Graduate How does Compton scattering suggest photons?
  • · Replies 5 ·
Replies
5
Views
2K
Graduate Few questions about photoelectricity
  • · Replies 2 ·
Replies
2
Views
2K
High School Compton’s experiment vs ordinary mirror
  • · Replies 8 ·
Replies
8
Views
2K
Relationship between spectral distribution and Compton scattering
  • · Replies 13 ·
Replies
13
Views
2K