Why the photoelectric absorption section finite at threshold

In summary, the conversation discussed the photoelectric effect of the hydrogen atom and its strange behavior. The Fermi golden rule states that the absorption rate is proportional to the density of the final states, but at threshold, the electron has zero momentum and therefore zero density of state. This would suggest that the absorption coefficient should be zero, but this argument is flawed because exactly zero momentum is not a proper state. Instead, every finite transition time gives a small momentum range, meaning that close to the threshold, the absorption section should still be close to zero. However, in reality, it is finite.
  • #1
zweiling
4
0
I mean the photoelectric effect of the hydrogen atom.

It is weird. By the Fermi golden rule, the transition or absorption rate is proportional to the density of the final states. At threshold, the electron has zero momentum and thus zero density of state. Therefore, the absorption coefficient should be zero at the threshold. Where does this argument go wrong?
 
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  • #2
Exactly zero momentum is not a proper state. Every finite transition time gives a small momentum range.
 
  • #3
mfb said:
Exactly zero momentum is not a proper state. Every finite transition time gives a small momentum range.
anyway, close to the threshold, the absorption section should be close to zero. But in reality, it is finite.
 

1. Why does the photoelectric absorption section become finite at threshold?

The photoelectric absorption section becomes finite at threshold because at this point, the photon energy is just enough to eject an electron from the atom. This is known as the binding energy of the electron, and any energy above this threshold will cause the electron to be ejected.

2. What determines the threshold for photoelectric absorption?

The threshold for photoelectric absorption is determined by the binding energy of the electron, which is specific to each atom. This energy is dependent on the atomic structure and can vary for different elements.

3. How does the photoelectric absorption process work?

The photoelectric absorption process occurs when a photon with enough energy strikes an atom and ejects an electron. The photon transfers its energy to the electron, causing it to gain enough energy to overcome the binding energy and leave the atom.

4. Why is the photoelectric absorption section important in understanding atomic structure?

The photoelectric absorption section is important in understanding atomic structure because it provides information about the binding energy of electrons in different atoms. This can help us understand the arrangement of electrons in an atom and how they interact with photons.

5. Can the photoelectric absorption section ever be infinite?

No, the photoelectric absorption section cannot be infinite. This is because there is a maximum amount of energy that a photon can transfer to an electron, which is equal to the photon's energy. Once this energy is transferred, the electron will no longer be bound to the atom, and the absorption process will cease.

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