Series 1 Blog Post 2: Electron-Positron Annihilation
As stated before, low energy electron-positron gives rise to two low energy gamma ray photons that move in opposite directions. Gamma rays exist as photons, and so gamma ray is just a photon with a high energy level, but we consider it as low energy level in annihilation reactions, as there are higher energy levels out there!
Now, why exactly can only low-energy photons be produced under these conditions?
In my previous blog post, I introduced you to the concepts of conservation of momentum and energy during annihilation reactions. Since this electron-positron has low energy, it can only give rise to another such subatomic particle which has low energy levels as well as the same momentum as itself.
Now let’s use some numbers to better understand what I mean by these conservations. The rest mass (which is nothing but the mass of a body measured when it as rest) of both positron and electron, is 0.511 MeV (M stands for million and eV is a symbol for electron volt). Electron volt is a unit to measure energy, and it is the amount of energy an electron gains after being accelerated by one volt of electricity. If we sum that up, because we have two particles with 0.511 MeV (0.511 + 0.511), we get the total rest mass as 1.022 MeV. Now, keeping that value in mind, note that one photon has an energy of 0.511 MeV as well. Having two photons, if we do the same calculation, both photons will have a total energy of 1.022 MeV. And le voilà ! They are both equal and hence the law is proved true for energy.
I will continue this tomorrow everyone! Thanks for reading my work!
Quantum Effects 