Compton scattering angle question

• Borg
In summary, it depends on the photon energy and electron. There is a continuous spectrum of energies in Compton scattering and there is a maximum change in energy. The minimum scattering angle is close to zero and the maximum angle would be 180 deg, but there is perhaps a higher probability that the scattering will be in between. There is also inverse Compton scattering whereby a higher energy photon is produced.
Borg
Gold Member
I've been reading some of my old physics books and I'm currently reading about Compton scattering. It got me to thinking - is there is a minimum Compton scattering angle? Is there a point where it becomes highly unlikely (or impossible) for a photon to be Compton scattered?

The answer depends on the photon energy and electron. For low energy photons, they are likely to be completely absorbed. As energy increases, photons are more likely to survive, and subject to Compton scattering. There is a continuous spectrum of energies in Compton scattering and there is a maximum change in energy. The minimum scattering angle is close to zero and the maximum angle would be 180 deg, but there is perhaps a higher probability that the scattering will be in between. Ostenstibly the result depends on the geometry of the interaction, and energies/momenta of the electron and photon.

There is also inverse Compton scattering whereby a higher energy photon is produced.
http://www.cv.nrao.edu/course/astr534/InverseCompton.html

Astronuc: I don't understand your answer. Compton scattering is a process between photons and free electrons. I don't think the photon can be absorbed, because then energy and momentum cannot both be conserved. Am I missing something?

phyzguy said:
Astronuc: I don't understand your answer. Compton scattering is a process between photons and free electrons. I don't think the photon can be absorbed, because then energy and momentum cannot both be conserved. Am I missing something?
From what I've been reading, a free electron can refer to an electron that has a small enough binding energy with respect to the photon energy such that the binding energy can be ignored and the electron can be considered 'free' (assuming, of course, that I'm remembering everything correctly ).

phyzguy said:
Astronuc: I don't understand your answer. Compton scattering is a process between photons and free electrons. I don't think the photon can be absorbed, because then energy and momentum cannot both be conserved. Am I missing something?
I was referring generally to photon-electron interactions. Also, Compton scattering can occur with atomic electrons, which are bound by energies on the order of ev (e.g. valence electrons) or keV for first orbital electrons of heavier elements.

Those energies compare to X-ray photons with energies (originating from electrons falling into the K or L shells) in the keV range or gamma rays of keV or MeV energy.

Astronuc said:
The answer depends on the photon energy and electron. For low energy photons, they are likely to be completely absorbed. As energy increases, photons are more likely to survive, and subject to Compton scattering. There is a continuous spectrum of energies in Compton scattering and there is a maximum change in energy. The minimum scattering angle is close to zero and the maximum angle would be 180 deg, but there is perhaps a higher probability that the scattering will be in between. Ostenstibly the result depends on the geometry of the interaction, and energies/momenta of the electron and photon.

There is also inverse Compton scattering whereby a higher energy photon is produced.
http://www.cv.nrao.edu/course/astr534/InverseCompton.html

I guess that I should make some assumptions about my question. Let's say that I have a truly free electron that isn't bound and a photon interacts with it at an extremely small grazing angle such that the electron gets the least amount of energy possible.

Could the angle be so small that the wavelength shift would approach zero and the electron deflected so slightly that its velocity would be on the order of a walking speed?

Borg said:
I guess that I should make some assumptions about my question. Let's say that I have a truly free electron that isn't bound and a photon interacts with it at an extremely small grazing angle such that the electron gets the least amount of energy possible.

Could the angle be so small that the wavelength shift would approach zero and the electron deflected so slightly that its velocity would be on the order of a walking speed?
If that were the case, then I don't think it would be measurable. If a keV or MeV photon changed energy by 1 eV, that would be challenge to measure. It might be considered non-interacting.

Free electrons are probably moving at well beyond 'walking' speed if walking refers to velocities of a few m/s.

At thermal energies, ~0.0235 eV, neutrons move at about 2200 m/s. Electrons being about 1/1839 of the mass of a neutron, a free electron would have a higher speed.

Unless it has a high speed, as in a plasma, an electron would likely find a convenient + nucleus and bind with it.

Thank you, Astronuc.

What is Compton scattering angle?

Compton scattering angle is the angle between the incident photon and the scattered photon in Compton scattering. It is an important concept in understanding the interaction between photons and matter.

How is the Compton scattering angle calculated?

The Compton scattering angle can be calculated using the formula θ = arccos[(λ' - λ)/λ], where θ is the scattering angle, λ' is the wavelength of the scattered photon, and λ is the wavelength of the incident photon.

What factors affect the Compton scattering angle?

The Compton scattering angle is affected by the energy of the incident photon, the atomic number of the scattering material, and the angle of incidence of the photon.

Why is the Compton scattering angle important in medical imaging?

The Compton scattering angle is important in medical imaging because it allows us to measure the energy of the scattered photons, which can be used to create images of the internal structures of the body. This is particularly useful in techniques such as X-ray computed tomography (CT).

How does the Compton scattering angle help us understand the behavior of photons?

The Compton scattering angle helps us understand the behavior of photons by showing us how they interact with matter and how their energy changes as a result of this interaction. This is crucial in fields such as quantum mechanics and nuclear physics.

• Atomic and Condensed Matter
Replies
1
Views
1K
• Introductory Physics Homework Help
Replies
13
Views
1K
• High Energy, Nuclear, Particle Physics
Replies
21
Views
3K
• High Energy, Nuclear, Particle Physics
Replies
2
Views
1K
• Quantum Physics
Replies
2
Views
5K
• Quantum Physics
Replies
1
Views
2K
• Introductory Physics Homework Help
Replies
10
Views
662
• Quantum Physics
Replies
8
Views
1K
• High Energy, Nuclear, Particle Physics
Replies
9
Views
2K
• Quantum Physics
Replies
6
Views
2K