question for astronomy

Question

The positron produced in the first step of the pp-chain almost immediately finds an electron and annihilates, e − + e + → γ. How much energy is released by this reaction? mγ = 0.

Answer 1

When two particles annihilate, all of their mass is converted into energy in the form of a photon. The mass of an electron (or a positron) is 9.10938356 × 10^-31 kg, but this problem is a lot easier to work with if we use the mass of an electron in electron volts per c², where c is the speed of light, and the electron volt is a unit of energy (just like the Joule). In this unit system, the mass of an electron is 0.511 Mev/c². So now we calculate the total mass of the electron positron system. mass_ele = 0.511 MeV/c² and mass_pos = 0.511 MeV/c². Total mass = 1.022 MeV/c². To compute the amount of energy released, we use Einstein's famous E = Mc². Now you will see why we used this unit system. E = (1.022 MeV/c²)*c². The c² cancels and we get an energy of 1.022 MeV or 1.63742445*10^-13 Joules