Where are positrons found?

Answer 1

Positrons are anti-electrons. They're antimatter. They don't generally "hang around" in our "regular matter" universe very long. They can be created in a type of radioactive decay called beta plus decay. That means that any radioisotope that decays by beta plus means will create some.

We also find positrons here and there where high energy gamma rays are present. That's because gamma rays of sufficient energy will create electron-positron pairs (in an even called -- no surprise -- pair production) if those gamma rays pass close to atomic nuclei.

During stellar nucleosynthesis, the process powering most stars, positrons are created in astronomical numbers. These positrons are "contained" within the star and add energy to the fusion process within the star.

Because positrons find an electron to "combine" with in mutual annihilation, we don't "find" positrons around much. In an antimatter universe, they'd be circling the nuclei of antimatter atoms just like the electrons form up around the nuclei of the "regular" atoms in our universe.

Answer 2

There are no positrons in an atom. A positron is an anti-electron - it's antimatter. It will combine with an electron when it can (pretty much as soon as it can) in mutual annihilation. Both it (the positron) and the electron will have their entire mass converted into energy. In translation, that means a positron (antimatter) will not survive in a "regular" matter universe. It won't exist here with us for very long. But the positron can appear here at any time. Let's look at that.

A positron can be created in a nuclear (radioactive) decay event. This is beta plus decay, and is addressed in the question about what beta decay is. In short, a proton is converted into a neutron in the nucleus of an atom and a positron is produced and kicked out of that nucleus. It did not exist in there before the event. Links to what beta decay is and other related posts can be found below.

A positron could also be created when a high energy gamma ray passes close to an atomic nucleus. This is called pair production. A question exists here that speaks to that and it is linked below.

In an antimatter universe, the positron would be in the positron cloud that forms about the nucleus of an antimatter atom. That nucleus would hold the anti-protons and the anti-neutrons.