Appeared and soon disappeared
The word 'antiparticle' sounds mysterious. And yet the antiparticle of a particle is simply that particle with the same mass but opposite electrical charge. One could also speak of 'complementary' or 'mirror' particles. Each of the twelve matter particles has an antiparticle, and all of these antiparticles have already been detected experimentally. The positron (antiparticle of the electron) and other antiparticles can be found in nature, namely in the radiation falling down on Earth from outer space. Wherever energy is converted into matter – be it during the Big Bang nearly 14 billion years ago, be it in the collision of cosmic radiation in the atmosphere, be it at CERN in Geneva – a similar amount of matter and antimatter is generated.
When matter and antimatter are brought together, they disintegrate and produce energy. This mechanism could in principle be used to build a bomb. The explosion of one gram of matter with one gram of antimatter would release as much energy as a small atomic bomb. The production of the necessary antimatter would however cost a lot of energy and time, making the construction of such a bomb unrealistic. Antimatter is used on the other hand in medicine (positron emission tomography), and this since 40 years already.