Questions about Antimatter

[petrushkagoogol]

Do free positrons exist in nature ? 

[petrushkagoogol]

As matter is composed of atoms, what is antimatter composed of ? 

[A-wal]

Atoms of the opposite charge.

[CraigD]

Do free positrons exist in nature ?

Yes.

 

Positrons are produced by nearly everything in nature – for example, the decay of naturally occurring ⁴⁰K isotope found in a single human’s body, produces about 4000 positrons each day. However, because they annihilate upon contact with their antiparticle, the electron, most positrons exist only briefly in nature.

 

I know of no natural phenomena that allows positron or other subparticles of antimatter to survive for long periods. There’s simply too much ordinary matter everywhere in the universe for it to annihilate with. Tiny amount of antihydrogen - each atom consisting of a positron and an antiproton – have been made and stored for periods of many days in manmade systems like the various “antimatter factories” such as CERN’s ATHENA and ALPHA.

 

(sources: Wikipedia article “positron”, CERN antimatter webpage)

[CraigD]

As matter is composed of atoms, what is antimatter composed of ?

Atoms of the opposite charge.

Since most atoms – those that aren’t ions – have zero net charge, I think A-wal’s answer, while on the right track, is a little inaccurate.

 

The particles in atoms of antimatter that have opposite charge compared to their normal atomic matter counterparts are the elementary charged particles that make up the atoms/anti-atoms – electron/positrons and quarks/antiquarks.

 

It’s interesting to note that electron/positrons and quark/anti-quarks make up only a small fraction, about 2% of the mass/energy of an atom or anti-atom. Most of the mass of atoms come from the gluons that bind the quarks into the protons/anti-protons and neutrons/anti-neutrons in the atoms/anti-atom’s nucleus. The gluon is its own antiparticle, which is a way of saying it has no antiparticle, so most of the mass in both ordinary atoms and anti-atoms comes from the same particle, the gluon.

 

It’s also worth noting that while artificially produced anti-hydrogen (1 positron + 1 anti-proton) is common place enough to be an everyday experimental commodity used in physics experiments, anti-helium (2 positrons + 2 anti-protons + 2 anti-neutrons) is exceedingly rare, and has never been stored for more than fractions of a second. For example, a 2011 experiment using the RHIC’s STAR detector detected a total of 18 anti-helium nuclei resulting from 1,000,000,000 high-speed collisions of gold nuclei (see “Observation of the antimatter helium-4 nucleus” 2011 STAR collaboration). To the best of my knowledge, an anti-helium nucleus has never been artificially mated with 2 positrons to make a neutral anti-helium atom.

[A-wal]

As matter is composed of atoms, what is antimatter composed of ? 

Atoms whose charged bits have the opposite charge.