What is antimatter and how is it used?

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Schematic representation of gamma radiation being split into electron particle (matter) and positron particle (antimatter)

Jagoda Urban-Klaehn
Idaho American Nuclear Society (ANS) Board Member
Radiation & Positron Spectroscopy
Isotope Production & Co-Assay
Idaho National Laboratory

Antimatter might sound like something out of a sci-fi movie, but it’s more fact than fiction. Antimatter is a mirror reflection of matter that was originally created in the Big Bang, in the very beginning of the universe. Antimatter particles are used in the medical field as a diagnostic tool and in scientific research to learn more about materials Positrons are the most common particles of the anti-matter, they are usually harmless and they are all around us. In simple form, positrons are like electrons, but have reversed properties. While electrons have a negative charge, positrons have a positive charge. Historical documentation shows the Greeks understood how electrons worked via electric static charge, but positrons are a fairly new discovery that were first documented in the early 1930’s.

How does antimatter form?
Antimatter is formed when high energy radiation is transformed into positrons and electrons {Fig.1}. This process is reversible since when positron encounters an electron it converts back into pure energy as outlined by Albert Einstein’s famous formula, E= mc2. This collision (that forms antimatter) happened in big quantities in the very beginning when the universe was created and it also happens during the formation of stars in distant galaxies. In small amounts it is continuously happening around us because positrons are created in radioactive elements and when they interact with electrons, they “annihilate”. Positrons disappear by annihilation because there are more electrons than positrons, so we have enough electrons to annihilate all the positrons, but not the vice-versa. The energy and radiation released during annihilation is significant enough that scientists can detect it using special equipment and play, “catch the positron.”

The positron annihilation process leaves a signal. These signals are used in a wide array of applications. One of those applications, as mentioned above, is in medical diagnostic equipment. Positron emission tomography (PET) is a commonly used imaging technique that helps reveal how your tissues and organs are functioning. These scans can sometimes detect diseases well before other imaging tests.

So yes, antimatter is all around us, within us and is helping researchers find ways to make better materials and to help save lives.

Under specific conditions in materials with no conductive (free) electrons – positrons and electrons can form positronium atom which is similar to hydrogen atom except that instead of heavy proton being surrounded by electron (like the Earth orbiting around the Sun), we have a binary system, that means electron and positron orbit each other like binary stars [Fig.2]. Positronium can live 1000 times longer than a free positron, because it does not have a charge therefore it does not attract electrons, since the electron and positron in positronium cancel each other charges.

While you might be hesitant to permit medical equipment that uses antimatter, it’s important to note that your body contains a small number of positrons that are continuously being annihilated. A naturally occurring radioactive potassium (called potassium-40) produces about 4000 positrons per day in the average human body. The PET scan contains such trace levels of antimatter that the risk of bodily harm is low.

There are even more fundamental applications for positrons in nuclear and material spectroscopy. Researchers use them as sensors for a material’s micro-structure. Ephemeral positrons can play hide-and-seek with electrons and find themselves stuck in a materials’ defect. In these hiding places called “traps,” positrons can live longer before annihilation. Scientists can measure how long positrons survive in these traps, which then tells them how many of these traps exist in a material and what the traps look like (how large or small).

This process helps researchers to learn about the structure of a material too small to see, even using microscopic equipment. Once researchers identify the structure of the material, they can learn how to better use it.

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