Positronium

Positronium is an exotic atom, which consists of an electron and its antiparticle, the positron. Clearly it is a hydrogen atom, in which the proton of the nucleus has been replaced by a positron.

Properties

A distinction is made between ortho-and parapositronium. While the spins of the electron and positron ( each 1/2) are rectified when orthopositronium, the total spin of the system ie 1 is, they are oriented in opposite directions parapositronium, whereby the total spin is 0 here.

Electron and positron annihilate, so that the positronium has only a finite life. Parapositronium decays with a mean lifetime of 0.125 ns into two photons. Orthopositronium can decay for reasons of invariance under charge conjugation only in an odd number of photons on the grounds of Lorentz invariance (energy - momentum conservation ) that is at least three. Since this process is less likely it is 142 ns, the considerably longer life.

To calculate the radius in the ground state Bohr's atomic model is sufficient:

This corresponds to twice the radius of the electron shell of the ground state of the hydrogen atom (the mass of the electron and the mass of the positron ).

Prediction and discovery

Was theoretically predicted the positronium atom in 1932 by Carl David Anderson and eg Stjepan Mohorovičić. The first evidence succeeded in 1951 the physicist Martin German at the Massachusetts Institute of Technology.

Compounds

Di - positronium

Di - positronium, or dipositronium, is a molecule of two positronium atoms and thus an analogy to the hydrogen molecule from two normal hydrogen atoms. The existence was predicted by John Archibald Wheeler in 1946 and described theoretically, but the molecule could be produced experimentally only in 2007 by David Cassidy and Allen Mills and proven.

Positronic water

Positronic water is a hypothetical water-like molecule consisting of one oxygen and two Positroniumatomen. Compared to the normal water so the hydrogen atoms are replaced by positronium.

The possibility of the existence of positronischem water was released by the American physicists Marquette University for the first time in 1998. On the basis of Monte Carlo simulations, they predicted that positronic water can exist quite true, but it is chemically not as stable as normal water, because the binding energy is only about 30% as large. In addition, a Annihilationsrate 4.6 ns -1 is predicted.

In practice positronic water has not yet been established.