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Welcome to our Physics lesson on Definition of Elementary Particles. Antiparticles, this is the second lesson of our suite of physics lessons covering the topic of Elementary Particles, you can find links to the other lessons within this tutorial and access additional physics learning resources below this lesson.
Elementary particles represent the smallest known building blocks of the universe. They are thought to have no internal structure, meaning that they are considered as as zero-dimensional points that occupy no space. Electrons are probably the most familiar elementary particles, but the Standard Model of physics, which describes the interactions of particles and almost all forces, recognizes in total 10 elementary particles. Some of them originate from outside the Solar System, so we can identify a number of elementary particles only through the radiation coming from remote stars by means of cosmic rays, which provide one of our few direct samples of matter from outside the solar system.
Cosmic rays are fluxes of high-energy particles that move through space at high speeds, very close to the speed of light. Most cosmic rays are atomic nuclei stripped of their atoms with protons (hydrogen nuclei) being the most abundant type but nuclei of elements as heavy as lead have been identified as well. In cosmic rays however, we also find other subatomic particles like neutrons, electrons and neutrinos.
In 1931, Paul Dirac - a famous British scientist of 20th century - based on theoretical reasoning, introduced the revolutionary hypothesis that besides the negative electron, there must exist the positive electron as well. This new particle must have a positive charge of +e and a spin of 1/2. (It cannot be proton, as a proton has no spin). Later on (in 1934) the positive electron (in short positron) was identified experimentally in cosmic rays coming from remote sources and immediately after this event, positron was also detected in terrestrial conditions. This elementary particle was identified as a particle produced by radiation emitted by radioactive nuclei of Phosphorus-30.
The related but opposite elementary particles such as electron and positron are known as antiparticles. More precisely, an antiparticle is a subatomic particle having the same mass as a given particle but opposite electric or magnetic properties.
There are many other antiparticles besides the electron-positron pair. As seen in beta decay examples explained in tutorial 20.3 "Radioactivity and Half-Life", electron is symbolically denoted as (e-) or (0/-1e) while positron as (e+) or (0/+1e). In the following paragraph, we will explain more in detail the electron-positron relationship and the interaction between them.
You have reached the end of Physics lesson 21.1.2 Definition of Elementary Particles. Antiparticles. There are 4 lessons in this physics tutorial covering Elementary Particles, you can access all the lessons from this tutorial below.
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