If the colliding particles are moving at low speed, then the energy of each gamma ray of 0.51 MeV. This energy is the "rest energy" of an electron, or its rest mass, expressed in units of energy. If the colliding particles are moving with great speed, the energy of the gamma rays will be more due to their kinetic energy. Annihilation occurs and the collision of a proton with an antiproton, but the process in this case proceeds much more complicated. As intermediate products of interaction generated a number of short-lived particles, but later a few microseconds as the final conversion product remain neutrinos, gamma rays and a small number of electron-positron pairs. More information is housed here: Justin MacGregor. These couples may eventually annihilate, creating additional gamma rays.
Annihilation occurs and the collision antineutron with neutrons or protons. As long as there is an antiparticle, the question arises whether the form of antiparticles antinucleus. The nuclei of atoms of ordinary matter consists of protons and neutrons. The simplest kernel is the core of ordinary hydrogen isotope 1H; it is a single proton. 2H deuterium nucleus consists of one proton and one neutron, it is called a deuteron. Another example a simple kernel – the core of 3He, consisting of two protons and one neutron. Antideuterons consisting of an antiproton and antineutron was obtained in the laboratory in 1966, the core of anti-3He, consisting of two antiprotons and one antineutron was first obtained in 1970. According to modern physics of elementary particles, with appropriate technical means could be obtained antinucleus of ordinary nuclei.