Antideuteron

Composite antiparticle consisting of an antiproton and an antineutron, first produced with a 30-GeV (giga-electron volt) synchrotron at Brookhaven National Laboratory, Long Island, N.Y., in 1965. Having a charge of negative one unit and an atomic mass of two units, it may be considered as the antinucleus of the hydrogen isotope deuterium.