Your Body Makes Antimatter Right Now

Your body is a source of antimatter, and it has been since before you were born. Not a metaphor: more than a hundred real antimatter particles leave the atoms inside you every hour.

The reason is potassium. Your nerves cannot work without it, and every bit of potassium on Earth contains the same tiny fraction of potassium-40, a radioactive isotope. A 70 kg adult carries about 17 mg of it, and thousands of those nuclei decay every second. Almost every time, the decay throws out an electron. About once in a hundred thousand decays it throws out a positron instead: the electron's antimatter twin.

At that rate a 50-second video is long enough. About two are expected while you watch, so the odds that one appears before the end are close to nine in ten.

A positron does not get far. Within about a millimeter it meets an ordinary electron, both are annihilated, and two gamma rays leave the spot in opposite directions. Catching that back-to-back pair is what a PET scanner is built to do. It could not image you from your own potassium, though: a scan relies on an injected tracer that is vastly stronger.

Sources, in the order the video uses them:
Share of potassium that is potassium-40 (0.0117 %), the positron branch (0.00103 % of decays, about one in a hundred thousand), and the positron's energy (482 keV maximum, 252 keV average) - DDEP decay-data table for K-40, LNHB, updated 2025: http://www.lnhb.fr/nuclides/K-40_tables.pdf
About 140 g of potassium and 17 mg of potassium-40 in a 70 kg adult, 266,000 decays per minute (about 4,400 per second) - Harvard Natural Sciences Lecture Demonstrations, quoting Shapiro, Radiation Protection: https://sciencedemonstrations.fas.harvard.edu/presentations/radioactive-human-body
"More than 4000 positrons per day, about 180 per hour" - Symmetry magazine, "The particle physics of you" (Nov 2015): https://www.symmetrymagazine.org/article/the-particle-physics-of-you
"About a millimeter" is our inference from the DDEP positron energies, which are close to those of fluorine-18, the standard PET isotope; it is not a range measured for potassium-40. The two opposite gamma rays are standard annihilation physics and carry no separate source here.
Background only, not a number in the video: the 2023 KDK measurement of potassium-40's rarest decay branch, already included in the DDEP table (abstract read) - Physical Review Letters 131, 052503: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.131.052503