Radioactive decay annihilation radiation

Gamma rays are high-energy electromagnetic radiation, and gamma radiation is almost always emitted when other radioactive decay occurs. Gamma rays usually aren t written into equations because neither the mass number nor the atomic number is altered. One exception is the annihilation of an electron by a positron, an event that only produces gamma radiation ... 

The fifth type of radioactive emission, gamma radiation, does not result in a change in the properties of the atoms. As a result, they are usually omitted from nuclear equations. Gamma emissions often accompany other alpha or beta reactions—any decay that has an excess of energy that is released. For example, when a positron collides with an electron, two gamma rays are emitted, a phenomenon usually referred to as annihilation radiation. 

A gamma-ray line at 0.511 MeV results from the mutual annihilation of an electron and a positron, a particle-antiparticle pair. A number of radioactive decay chains (see Table I) result in the emission of a positron as a decay product, which will annihilate upon first encounter with an electron. Also of astrophysical importance is the production of electrons and positrons via the photon-photon pair-creation process. Such pair plasmas are found in the vicinity of compact objects, such as neutron stars and black holes, that are associated with heated accretion disks and relativistic flows and jets, within which particle acceleration is known to occur. Thus, relatively narrow lines of 0.511-MeV annihilation radiation are expected to arise in the interstellar medium through the decay of dispersed, nucleosynthetic radionuclides, while broadened, Doppler-shifted, and possibly time-variable lines may occur in the high-energy and dense environments associated with compact objects. 

As discussed previously, when an expl is irradiated with fast neutrons a N nucleus captures the incident fast neutron and ejects two slow neutrons. The resulting nucleus, N, is excited (radioactive) and decays with a io min half-life to stable C. In this last transition, a positron, 3<-, is emitted. Because of its opposite charge, the J3+ is strongly attracted by a nearby electron in the resulting collision, both the positron and electron are annihilated and in the process of annihilation, the masses of the colliding particles are converted into two 0.511 MeV quanta of electromagnetic radiation. These 7rays are what are detected to indicate the possible presence of an expl... 

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