Today I am going to write about Compton effect and inverse Compton effect. Most of the students of physics and chemistry is familiar with the first one but I assure you both of them are equally interesting. So, let's jump in.

Compton effect

CC-BY 3.0 By JabberWok | Compton effect
Compton effect was discovered by an American physicist Arthur Holly Compton and this effect has huge importance in quantum mechanics. So, what is this effect? Well, when a photon with high energy hit an electron (initially at rest), the photon loses energy. The electron gets this energy lost by the photon and starts to move. So, the energy lost by the photon is now the kinetic energy of the electron. You can ask me what happens to the photon? It scatters away with an angle and as it lost some energy, its frequency decrease or in other words wavelength increase. This phenomenon is known as the Compton effect. Here, is the equation which describes the Compton effect-

Here, is the wavelength of the photon after collision and is before the collision. h/mc is known as the Compton wavelength. The angle can reach highest up to 180 degrees. In that case, change in wavelength is 2 times of the Compton wavelength.

Compton effect has its vast application in medical physics and biology. It is widely used in radiation therapy as high energy gamma or x-ray photon can interact with the atoms of living creatures.

Inverse Compton effect

This effect is also known as the Sunyaev-Zeldovich effect. So, as the heading goes it is inverse of the Compton effect. In Compton effect, the photon had a very high energy and electron was in rest but here quiet opposite. This effect is not that known like the Compton effect cause its application is mostly in the interstellar medium. So, photons can belong to cold sources. For example, 2.7 K background. It can interact with a hot source like a cluster of galaxies and these galaxies have a lot of free electrons with a temperature of 10⁷ Kelvin. So, the effect will happen complete opposite to the Compton effect and the photon from a higher wavelength will shift to a lower wavelength. In Compton effect energy was lost by the photon and gained by the electron but here energy is lost by the electron and gained by the photon.

photo credit : me

The fraction of energy loss =

As a result, there is a fractional change in the background temperature which is shown in the equation below-

Here, T is temperature, is Thomson cross-section and LN_e is the linear density of the electron.

This effect is very useful.For example, comparing this result with the x-ray emission map we can easily find the distance without taking redshift into account and can also be used to determine the Hubble's constant. That's all for today. Have a nice weekend.

Reference

1. Kristen Rohlfs, Tools of radio astronomy

2. Dejan Urosevic, Introduction to the theory of radio astronomy

3. Mirjana Vukicevic, Theoretical Astrophysics