I thought proof of anti-matter was rare, if any proof at all. Yet, Googling about PET scans, many articles casually say the imaging is produced by positrons, like it’s no big deal. Nonetheless, I cannot readily accept PET scans create a stream of positrons? If true as claimed, how is this possible? And, even more puzzling, why aren’t these positrons instantly destroyed by their counterparts, the electron, in a violent explosion? I thought matter and anti-matter were to instantly eliminate each other in quite a violent manner. So, what gives? :dubious:
A PET scanner detects the matter antimatter annihalation event by looking for a pair of gamma rays that arrive at close to the same time but in opposite directions from a point inside the scanner. Conservation of momentum requires that an electron positron pair emit two such photons. So the scanner detects the place a positron was. It doesn’t make them itself. To get the positrons into the subject you inject a radiotracer that contains a suitable radioactive substance. In this case usually fluorine-18.
No, not rare at all. Many radioactive isotopes produce positrons when they decay. Antiprotons are produced in large numbers in particle accelerators. Wikipedia page on antimatter has a lot of information on it.
PET scans work by injecting radioactive isotopes which are bound to certain molecules. Those isotopes produced positrons when they decay.
They are. Each positron is almost instantly destroyed by annihilating with an electron and releasing a lot of energy. This energy goes into creating a pair of high-energy gamma ray photons. That’s what the PET scanner detects.
It doesn’t produce an explosion because there’s not enough of the radioactive material.
Or if you prefer, it does produce a bunch of explosions, just really, really tiny ones.