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Updated: Jun 27, 2020

By Oleksandr Koliakin

The positronium is an exotic atom, made out of an electron and an antielectron (positron) orbiting around each other. Unlike in 'normal' atoms, where leptons orbit a nucleus made out of baryons or mesons, in positronium atoms the electron and positron are sort of 'chasing each other in circles'.

This is an atom of positronium, made up of an electron and a positron. Positronium atoms are highly unstable, because the positron and the electron tend to annihilate each other.
An atom of positronium

The chemical representation of positronium is Ps.

Atoms (if we can call them that) of positronium can appear when a positron that is slowed down while traveling through matter is captured by an electron. However, positroniums are highly unstable, the particles that it is made out of usually annihilate each other. In fact, the mean half life of a positronium is about one-tenth of a nanosecond (and a nanosecond is one billionth of a second)


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