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Electron capture happens most often in the heavier neutron-deficient elements where the mass change is smallest and positron emission is not always possible. When the loss of mass in a nuclear reaction is greater than zero but less than 2m e c 2 the process cannot occur by positron emission, but occurs spontaneously for electron capture.
The two types of beta decay are known as beta minus and beta plus.In beta minus (β −) decay, a neutron is converted to a proton, and the process creates an electron and an electron antineutrino; while in beta plus (β +) decay, a proton is converted to a neutron and the process creates a positron and an electron neutrino. β + decay is also known as positron emission.
If the mass difference between the parent and daughter atoms is more than 1.022 MeV/c 2 (two electron masses), another decay is accessible, capture of one orbital electron and emission of one positron. When the mass difference is more than 2.044 MeV/c 2 (four electron masses), emission of two positrons is possible. These theoretical decay ...
If the mass difference between the mother and daughter atoms is more than two masses of an electron (1.022 MeV), the energy released in the process is enough to allow another mode of decay, called electron capture with positron emission. It occurs along with double electron capture, their branching ratio depending on nuclear properties.
Potassium-40 undergoes four different types of radioactive decay, including all three main types of beta decay: electron emission (β −) to 40 Ca with a decay energy of 1.31 MeV at 89.6% probability, positron emission (β + to 40 Ar at 0.001% probability [1], electron capture (EC) to 40 Ar * followed by a gamma decay emitting a photon [Note 1 ...
Nuclei which decay by positron emission may also decay by electron capture. For low-energy decays, electron capture is energetically favored by 2m e c 2 = 1.022 MeV, since the final state has an electron removed rather than a positron added. As the energy of the decay goes up, so does the branching fraction of positron emission.
In physics, electron emission is the ejection of an electron from the surface of matter, [1] or, in beta decay (β− decay), where a beta particle (a fast energetic electron or positron) is emitted from an atomic nucleus transforming the original nuclide to an isobar.
Ar by either electron capture or positron emission. This latter decay branch has produced an isotopic abundance of argon on Earth which differs greatly from that seen in gas giants and stellar spectra. 40 K has the longest known half-life for any positron-emitter nuclide.