Antimatter

In modern physics, antimatter is defined as matter composed of the antiparticles (or "partners") of the corresponding particles in "ordinary" matter, and can be thought of as matter with reversed charges and parity, or going backward in time (see CPT symmetry). Antimatter occurs in natural processes like cosmic ray collisions and some types of radioactive decay. Antiparticles can also be generated at particle accelerators, but only a tiny fraction of these have successfully been bound together in experiments to form antiatoms. Total artificial production has been only a few nanograms. No macroscopic amount of antimatter has ever been assembled due to the extreme cost and difficulty of production and handling. Nonetheless, antimatter is an essential component of widely available applications related to beta decay, such as positron emission tomography, radiation therapy, and industrial imaging. In theory, a particle and its antiparticle (for example, a proton and an antiproton) have the same mass, but opposite electric charge, and other differences in quantum numbers. A collision between any particle and its anti-particle partner leads to their mutual annihilation, giving rise to different proportions of intense photons (gamma rays), neutrinos, and sometimes less-massive particle–antiparticle pairs. The majority of the total energy of annihilation emerges in the form of ionizing radiation. If surrounding matter is present, the energy content of this radiation will be absorbed a