Positron

Positron ( e )

The positron ( portmanteau of positive charge and electron), symbols, is an elementary particle from the group of leptons. It is the antiparticle of the electron, with which it coincides up to the sign of the electric charge and the magnetic moment in all its properties.

Meeting a positron and an electron each other can occur a pair annihilation ( annihilation). In an ideal vacuum, in which there are no electrons, positrons, however, are stable.

The positron was the first known antiparticle. Its existence was predicted in 1928 by Paul AM Dirac. Carl David Anderson discovered experimentally on August 2, 1932 in cosmic rays and gave him his name. Since the quantum mechanical properties of all the electrons apart from charge and helicity same pair of concepts positron Negatron for the two variants of the electron has been proposed. The term Negatron has however not enforced and is used only occasionally in the literature today.

Formation

Positrons arise

• The β -decay ( one of the two types of beta decay ),
• The decay of positive muons (eg from cosmic rays )
• And pair production in high-energy collision processes, namely: Interaction of hard gamma radiation with matter,
• Experiments at particle accelerators,
• Interaction of cosmic rays with the Earth's atmosphere,
• Terrestrial gamma-ray bursts.

In a normal environment "disappear" positrons within a short time by mutual annihilation with electrons. Only in a very good vacuum positrons can be stored by magnetic fields.

Applications

Applications outside of positrons basic physics research is based on the special, easily identifiable radiation of the pair annihilation. In particular, positron emission tomography (PET ) is an important imaging technique in modern medical technology. In this case the patient is a positron-emitting radiopharmaceutical administered, namely, a substance found in human metabolism (eg glucose). In the molecule of that substance, a β - radioactive atom is either in addition to or in place of a coupled non-radioactive atom. Note, in nuclear medicine is that the radioactive isotope is a hand durable enough so that it mounted in a biomolecule and the production laboratory (usually a cyclotron facility ) can be brought to the patient, on the other hand, however, short-lived enough to allow imaging during measurement, but after this the patient no longer unnecessarily burdening with radiation. Mainly used in the tracer is FDG- PET 18, wherein a 19F atom by a radioactive atom substituted 18F (half-life 109,77 min). The glucose is metabolized increased from tissues with high energy requirements, such as tumors or brain, so there is a higher concentration than in other regions. This concentration is visually made ​​visible.