Positron
Definition and meaning of Positron in chemistry.
A positron is the antimatter twin of an electron. It has the exact same mass as an electron but carries a positive charge instead of a negative one. Positrons are created during a type of radioactive decay called beta plus decay.
In more detail
During beta plus decay, a proton inside an unstable nucleus converts into a neutron. This releases a positron and a neutrino at the same time. Because a positron is antimatter, it cannot exist near ordinary matter for long.
The instant a positron collides with a regular electron, both particles annihilate each other completely. Their entire combined mass converts into pure energy, following Einstein's famous equation, energy equals mass times the speed of light squared. This burst of energy comes out as two gamma ray photons flying off in opposite directions.
Doctors put this reaction to practical use in a medical scan called PET, short for positron emission tomography. Patients receive a small amount of a radioactive tracer that emits positrons. As those positrons annihilate with electrons inside the body, the resulting gamma rays are detected and used to build a picture of metabolic activity.
This makes PET scans especially useful for spotting cancer, since fast-growing tumor cells often use far more sugar than normal, healthy tissue does. Physicist Paul Dirac first predicted the positron mathematically in 1928. Carl Anderson then confirmed it experimentally in 1932, giving scientists their first real proof that antimatter exists.
Outside of a lab or a PET scanner, positrons rarely last long in the everyday world, since ordinary matter is everywhere.
Key facts
| Field | Physical Chemistry |
|---|---|
| Charge | +1 elementary charge |
| Antiparticle of | Electron |
| Formed by | Beta plus decay |
| Annihilation product | Two gamma ray photons |
| Medical use | PET scans (positron emission tomography) |
The radioactive isotope carbon-11 undergoes beta plus decay and turns into boron-11. In the process, it releases a positron and a neutrino, both flying away from the decaying nucleus.
Frequently asked questions
What happens when a positron meets an electron?
They annihilate each other instantly, converting their entire combined mass into pure energy, released as two gamma ray photons.
How are positrons used in medicine?
In PET scans, patients receive a tracer that emits positrons. These positrons annihilate with nearby electrons in the body, and detectors track the resulting gamma rays to map metabolic activity, often to find tumors.
Is a positron the same size as a proton?
No. A positron has the same mass as an electron, which is nearly 2,000 times lighter than a proton. Only its charge, positive instead of negative, resembles a proton.