MATTER AND ANTIMATTER

The proton, the neutron, and the electron each has its own nemesis particle that occurs in the form of antimatter. These particles are called antiparticles. The antiparticle for the proton is the antiproton; for the neutron it is the antineutron; for the electron it is the positron. The antiproton has the same mass as the proton, but in a negative sort of way, and it has a negative electric charge that is equal but opposite to the positive electric charge of the proton. The antineutron has the same mass as the neutron, but again in a negative sense. Neither the neutron nor the antineutron have any electric charge. The positron has same mass as the electron, but in a negative sense, and it is positively charged to an extent equal to the negative charge on an electron.
You might have read or seen in science-fiction novels and movies that when a particle of matter collides with its nemesis, they annihilate each other. This is true. What, exactly, does this mean? Actually, the particles don’t just vanish from the cosmos, but they change from matter into energy. The combined mass of the particle and the antiparticle is liberated completely according to the same Einstein formula that applies in nuclear reactions:
E = (m₊  +  m_-) c²
where E is the energy in joules, m₊  is the mass of the particle in kilograms, m_- is the mass of the antiparticle in kilograms, and c is the speed of light squared, which, as you recall, is approximately equal to 9 × 10¹⁶ m²/s².