positron

Examples of positron in the following topics:

• Emission Topography

  • Positron emission tomography is a nuclear medical imaging technique that produces a three-dimensional image of processes in the body.
  • Positron emission tomography (PET) is a nuclear medical imaging technique that produces a three-dimensional image or picture of functional processes in the body.
  • PET acquisition process occurs as the radioisotope undergoes positron emission decay (also known as positive beta decay), it emits a positron, an antiparticle of the electron with opposite charge.
  • The encounter annihilates both electron and positron, producing a pair of annihilation (gamma) photons moving in approximately opposite directions.
  • Discuss possibility of uses of positron emission tomography with other diagnostic techniques.

• Photon Interactions and Pair Production

  • For example, an electron and its antiparticle, the positron, may be created.
  • The photon must have enough energy to create the mass of an electron plus a positron.
  • The mass of an electron is $9.11 \cdot 10^{-31}$ kg (equivalent to 0.511 MeV in energy), the same as a positron.
  • The electron and positron can annihilate and produce two 0.511 MeV gamma photons.
  • A photon decays into an electron-positron pair.

• Matter and Antimatter

  • Matter-antimatter reactions have practical applications in medical imaging, such as in positron emission tomography (PET).
  • The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide (tracer), which is introduced into the body on a biologically active molecule.
  • For example, a positron (the antiparticle of the electron, with symbol e+) and an antiproton (symbol p-) can form an antihydrogen atom .
  • Antihydrogen consists of an antiproton and a positron; hydrogen consists of a proton and an electron.

• Beta Decay

  • Beta decay is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted from an atomic nucleus.
  • Beta decay is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted from an atomic nucleus, as shown in .
  • Beta minus (β) leads to an electron emission (e−); beta plus (β+) leads to a positron emission (e+).
  • In electron emission an electron antineutrino is also emitted, while positron emission is accompanied by an electron neutrino.

• Conservation of Nucleon Number and Other Laws

  • In beta decay, a nucleus releases energy and either an electron or a positron.
  • In the case of a positron being released, atomic mass remains constant as a proton is converted to a neutron, lowering atomic number by 1:
  • Electron capture has the same effect on the number of protons and neutrons in a nucleus as positron emission.

• X-Rays and the Compton Effect

  • Higher energy photons (1.022 MeV and above, in the gamma ray range) may be able to bombard the nucleus and cause an electron and a positron to be formed, a process called pair production.