Particle shower
A particle showers or cascade shower is in the particle a cascade of secondary particles , which arise when a high energy particle collides with dense matter. The incoming particle creates new particles with lower energy during the interaction. The new particles interact in a similar way until several thousand, millions or even billions of low-energy particles have been generated in the process. These are slowed down and absorbed by the surrounding matter.
In astronomy, a particle shower also means a meteor shower .
Shower types
There are two basic types of particle showers. Electromagnetic showers are created by particles that interact mainly or exclusively through the electromagnetic forces . These are usually photons or electrons . Hadronic showers are created by hadrons . These are e.g. B. nucleons and other particles made up of quarks . They interact largely through the Strong Nuclear Force .
An electromagnetic shower begins when a high-energy electron or photon enters a material. At high energy, photons interact primarily through pair production ; d. In other words , they transform into electron- positron pairs while they transfer their momentum to atomic nuclei or electrons in the material. High-energy electrons and positrons mainly generate photons ( bremsstrahlung ). These two processes continue alternately until the remaining particles have sufficiently small energy. Electrons and photons then lose their remaining energy through scattering until they are absorbed by atoms.
A hadronic shower is generated by a high energy hadron, such as B. a nucleon , a pion or an atomic nucleus . Such particles have an electrical charge and therefore produce showers, some of which are electromagnetic. But they also interact with the atomic nuclei via the strong nuclear force. Usually several hadrons with lower energy are created. This is repeated as with an electromagnetic shower, until all particles are braked or absorbed in the material.
Examples
Cosmic rays are constantly hitting the earth's atmosphere . In doing so, they create showers within the atmosphere. The first muons and pions were experimentally detected through these air showers . They are still used in some experiments today as a means of observation to observe ultra-high-energy cosmic rays (see GZK cutoff ). Some experiments, such as the Pierre Auger Observatory , observe the visible atmospheric fluorescence that occurs at the highest intensity of the shower and / or the remains of a shower in scintillation detectors on the ground.
In particle detectors in high-energy particle accelerators, a device called a calorimeter determines the energy of particles by creating showers of particles and then measuring their energy. Many large detectors have both an electromagnetic calorimeter and a hadronic calorimeter . Each type has been specially designed to generate and measure the energy of the corresponding shower type.
Web links
- "Passage of particles through matter" (PDF; 361 kB), by S. Eidelman et al .: Review of Particle Physics . In: Physics Letters B . 592, 2004, p. 1. (English; PDF file; 361 kB)
Individual evidence
- ↑ Köhn, C., Ebert, U., The structure of ionization showers in air generated by electrons with 1 MeV energy or less, Plasma Sources Sci. Technol. (2014), vol. 23, no.045001