Compton Scattering : What's it all about?

_{Image source - IG | doverun}

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From the image above, we can see Albert Einstein famous equation E=MC^2 which is known as the rest energy of a particle. Energy E=PC is for particles traveling at a relativistic speed having zero rest mass.
Where he is shooting off energy ball like a dragon ball character, we can see super energy is equal to several arrows facing towards different directions, plus P. But what does it mean? It's the conservation of momentum 'P'.

An incident photon with momentum P and energy PC collides with an electron which is at rest, its initial momentum is zero and its initial energy is its rest energy MC^2. The collision is elastic which causes the photon to deviate from its original path at an angle theta. Also this collision causes the photon to loss some energy to the electron which is now also in motion. Energy before the collision equals energy after the collision which means that momentum is conserved.

_{The arranged arrows from the first image.}

When X-rays strike matter, some of the radiation is scattered, just as visible light falling on a rough surface undergoes diffuse reflection.
Compton discovered that the deviated (scattered) radiation has smaller frequency (longer wavelength) than the incident radiation and that the change in wavelength depends on the angle through which the radiation is scattered.

note: as I am going slowly through the material, those who are interested are highly recommended to read this wiki's page