Antimatter is treated like an exotic substance, fraught with danger, which can only be harnessed in the future to send star ships to warp speed. However, this isn't true. We use antimatter right now, and we use it in hospitals. Learn how PET scans use positrons to help you.

Antimatter Ideas and Antimatter Reality

Antimatter is a simple concept. An antimatter particle is any particle that has the same mass as a regular particle, but with an opposite charge. If a particle of antimatter meets its corresponding particle of matter, the two take each other out, giving off massive amounts of energy. The idea was first seriously put forward by physicist Paul Dirac, in 1928, while he was tinkering with wave equations for electrons.


The idea sounds both insane and cool, and has been incorporated into all kinds of science fiction. Matter-antimatter matrices power star ships; alternate universes are made up of antimatter; conglomerations of antimatter threaten any world they get too near.

In the real world, antimatter is what seems to be threatened. Get it too close to anything in our world and it pops out of existence. It wasn't until 1995 that CERN was able to cobble together so much as an atom of antihydrogen.

Naturally Occurring Antimatter

Antimatter isn't something that needs to be created by humans, nor is it particularly exotic. Positrons — antielectrons which annihilate when they hit regular electrons — are being created all the time. To harvest them, all we need to do is get some of the material capable of giving them off.


One such material is fluorine-18. Fluorine-18 comprises nine protons and nine neutrons, but not for long; soon it slides down the periodic table of elements, one of its protons turning into a neutron via radioactive decay. The type of decay is called beta plus decay, or positron emission. When a proton turns into a neutron, it spits out a positron, which has the mass of an electron and a positive charge, and an electron neutrino, which also has a little mass but has no charge.

The positron isn't long for this world. When it encounters an electron, the two annihilate each other. In doing so, they give off a gamma ray, high energy rays that travel through many things... including human flesh.


A Positron Emission Tomography Scan

Gamma rays are not wonderful things to be exposed to, but they're safer than a scalpel, and under the right circumstances they can provide more information. When doctors want to see how organs in a body function, they break out a PET (positron emission tomography) scan. A person getting a PET scan gets a dose of fluorine-18 in a special form. Fludeoxyglucose harnesses fluorine-18 to glucose, the molecule the body uses to provide itself with energy, so the fludeoxyglucose will go to whatever organ is using energy. Sometimes that's a functioning brain. Sometimes it's a tumor.

Wherever it goes, the fluorine-18 will be decaying and emitting positrons. The positrons will meet electrons, and send out gamma rays. By detecting the origin of the gamma rays, the PET scan shows which organs are functioning in which ways. Granted, it's a lot less exciting than going to warp 9, but it is useful.


Top image: Liz West.

[Via Positron Emission Tomography, PET Scan, Positron Emission Tomography, PET Scan]