Electrons, Protons, and Neutrons are known as the fundamental particles of atoms. Electrons are placed in certain orbits surrounding nucleus. Protons and neutrons are placed within the nucleus that lies at the center of the atom. But, that does not mean that only these three particles are present in an atom. There is another particle which is involved in the transition of one particle to another with some charge.
What is positron?
Positron is a subatomic particle whose mass is same as that of electron and numerically equal but positively charged particle.
The collision of low-energy positron and a low-energy electron results in the formation of two or more gamma rays photon and this process is known as electron-positron annihilation. The two main processes of production of positron are radioactive decay and the pair production. The interaction between energetic photons with an atom in a material is known as pair production.
Mass of Positron in Amu
As we know, the mass of proton is 1.007593 amu or 1.6726231 x 10-27. Similarly mass of electron is 0.000548756 amu or 9.10093897 x 10-31 kg. The mass of positron is equal to mass of electron i.e., 0.000548756 amu. The exact value of the mass of positron is about 0.511 MeV/c2 or 9.11 x 10-31 kg.
Since positron is produced in radioactive decay by departing neutron, their kinetic energy is supported by their motion. According to the concept of conservation of energy and momentum, the positron loses some of its kinetic energy when it collides with the other particles. They come to rest position as a result of energy loss. The positron particles are ready to participate in an annihilation reaction after losing kinetic energy.
Rest Mass of Positron
The encounter of positron with an electron obeys the momentum or laws of energy conservation. These two particles together annihilate each other and transform all their mass to energy to form two photons.
The momentum of the system is zero because the positron and electron are almost at rest before annihilation and remain same after annihilation. Therefore, two photons travel in opposite directions and the net momentum is zero. The rest mass of the electron and positron are same that is 511 keV, therefore each photon has 511 keV of energy.
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