Page "Antiparticle" Paragraph 4

Antiparticles are produced naturally in beta decay, and in the interaction of cosmic rays in the Earth's atmosphere.

Because charge is conserved, it is not possible to create an antiparticle without either destroying a particle of the same charge ( as in beta decay ) or creating a particle of the opposite charge.

The latter is seen in many processes in which both a particle and its antiparticle are created simultaneously, as in particle accelerators.

This is the inverse of the particle-antiparticle annihilation process.