Exotic atom

As exotic atoms atom -like bound particles are referred to, in which one of the particles involved is at least not an ordinary atomic component, so no proton, neutron or electron.


The most important exotic atoms are:

  • Replacement of a shell electron by a negatively charged particles: Muonic atoms with a muon. The muon is because of its high mass very close to the atomic nucleus. Spectroscopy of muonic atoms therefore allows studies of the core structure.
  • Pionic and kaonische atoms with a pion or kaon (both mesons ). Simpelstes example is mesonic hydrogen consisting of a proton and a pion or kaon. Pion and kaon are due to its higher mass even closer to the nucleus than the muon of the muonic atoms. Unlike electrons interact pions and kaons, as they are mesons, not only via the electromagnetic, but also on the attractive or repulsive strong interaction with the nucleons of the nucleus. So be measured against pionic and kaonic atoms parameters for this interaction.
  • Protonium of a proton and an antiproton. Protonium has an extremely small radius, and has been demonstrated experimentally. Also other light atoms (helium, lithium) with an anti- proton instead of an electron ( " antiprotonisch " ) are possible in principle.
  • Positronium and muonium with a positron or a antimuon. Positronium and muonium consist exclusively of leptons. Because these are structureless present state of knowledge, so to speak, " point-like " to positronium and muonium are particularly suitable for high-precision investigation of the electromagnetic interaction and the measurement of fundamental constants of nature.
  • Antimatter, in which each atom component is replaced by its oppositely charged antiparticles, eg Antihydrogen, consisting of antiprotons and positrons in the core in the shell.
  • Muonic, pionic, kaonische and protonic antimatter, in a case positron is replaced by a positively charged anti - muon, pion, kaon, or by a proton.
  • Atoms of two mesons, in particular of two pions or a pion and a kaon


Except for the anti- atoms such as antihydrogen atom all of these exotic atoms are unstable and short-lived. Even anti- atoms are stable only as long as they do not come into contact with ordinary matter, since they annihilate else ( annihilation).


In nature, positronium, muonium and muonic atoms occur as secondary products of cosmic rays in very small amounts, as well as pionic or kaonische atoms, but still live much shorter. On Earth, the exotic atoms, also antihydrogen atoms are produced by particle accelerators sufficiently high beam energy.


The study of antihydrogen atoms in the European research center CERN to prepare a precise test of the symmetry between matter and antimatter. Are planned such experiments with higher accuracy at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt.


Template: Internet resource / maintenance / access date not in ISO format template: Internet resource / Maintenance / date not in ISO format Rudolf Gross:. Physics IV, Lecture Notes SS 2003 March 2003 accessed on 13 December 2009 (PDF 1.52 MB).