The Basic Process of Annihilation
Matter-antimatter annihilation is a fundamental physical process that occurs when a particle collides with its corresponding antiparticle. For instance, an electron colliding with a positron (its antiparticle) results in both particles disappearing. This event is governed by Einstein's mass-energy equivalence, E=mc², where the entire mass of the colliding particles is converted directly into energy.
Energy Release and Products
The energy released during annihilation is typically in the form of high-energy photons, most commonly gamma rays. The number and type of photons produced depend on the specific particles involved and their kinetic energy before the collision. For an electron-positron annihilation, usually two gamma-ray photons are produced, traveling in opposite directions to conserve momentum.
A Practical Example: PET Scans
A common practical application of matter-antimatter annihilation is found in Positron Emission Tomography (PET) scans, used in medical imaging. In a PET scan, a patient is injected with a radioactive tracer that emits positrons. When these positrons encounter electrons in the body, they annihilate, producing gamma rays. These gamma rays are then detected by the scanner, allowing for the creation of detailed images of metabolic activity within the body.
Significance in Physics and the Universe
Annihilation is crucial to our understanding of fundamental particle physics and the early universe. It is hypothesized that a slight imbalance of matter over antimatter in the early universe, where most antimatter annihilated with matter, is why the universe today is predominantly composed of matter. Scientists also study annihilation to understand fundamental particle properties and in theoretical concepts for future energy or propulsion systems.