Electron capture

Electron capture (K-electron capture, also K-capture, or L-electron capture, L-capture) is a process in which the proton-rich nucleus of an electrically neutral <a href="/facts/Atom/FoQ4kGN5">atom</a> absorbs an inner atomic <a href="/facts/Electron/L0KBo5cW">electron</a>, usually from the K or L <a href="/facts/Electron_shell/QxI30eh9">electron shells</a>. This process thereby changes a nuclear <a href="/facts/Charged_current_interaction/uJAQqxoj">proton to a neutron</a> and simultaneously causes the emission of an <a href="/facts/Electron_neutrino/e5hQPWIQ">electron neutrino</a>.

 <a href="/facts/Proton/clCjepXP">p</a>   +   <a href="/facts/Electron/L0KBo5cW">e−</a>     →    <a href="/facts/Neutron/oRCM1geb">n</a>   +  <a href="/facts/Electron_neutrino/e5hQPWIQ">νe</a> 
or when written as a <a href="/facts/Nuclear_reaction/202yClUr">nuclear reaction equation</a>, 
 
 
 
 
 
 e
 
 
 
 
 −
 1
 
 0
 
 +
 
 p
 
 
 
 1
 1
 
 ⟶
 
 n
 
 
 
 0
 1
 
 
 +
 
 0
 
 
 0
 
 
 
 
 
 {\displaystyle {\ce {^{0}_{-1}e + ^{1}_{1}p -> ^{1}_{0}n + ^{0}_{0}}}}
 
ν
 
 
 
 
 
 
 e
 
 
 
 
 {\displaystyle _{e}}

Since this single emitted neutrino carries the entire <a href="/facts/Decay_energy/g4wDGC8r">decay energy</a>, it has this single characteristic energy. Similarly, the momentum of the neutrino emission causes the daughter atom to recoil with a single characteristic momentum.
The resulting <a href="/facts/Daughter_nuclide/hT0obfLv">daughter nuclide</a>, if it is in an <a href="/facts/Excited_state/czcLYNnr">excited state</a>, then transitions to its <a href="/facts/Ground_state/ML7cfCug">ground state</a>. Usually, a <a href="/facts/Gamma_ray/5Drf913J">gamma ray</a> is emitted during this transition, but nuclear de-excitation may also take place by <a href="/facts/Internal_conversion/mVkoudEe">internal conversion</a>.
Following capture of an inner electron from the atom, an outer electron replaces the electron that was captured and one or more <a href="/facts/Characteristic_X-ray/Qw75UEha">characteristic X-ray</a> photons is emitted in this process. Electron capture sometimes also results in the <a href="/facts/Auger_effect/a0SVoK1r">Auger effect</a>, where an electron is ejected from the atom's electron shell due to interactions between the atom's electrons in the process of seeking a lower energy electron state.
Following electron capture, the <a href="/facts/Atomic_number/bgAr581S">atomic number</a> is reduced by one, the neutron number is increased by one, and there is no change in <a href="/facts/Mass_number/VyBbJ1oI">mass number</a>. Simple electron capture by itself results in a neutral atom, since the loss of the electron in the <a href="/facts/Electron_shell/QxI30eh9">electron shell</a> is balanced by a loss of positive nuclear charge. However, a positive atomic ion may result from further Auger electron emission.
Electron capture is an example of <a href="/facts/Weak_interaction/f6upmKMs">weak interaction</a>, one of the four fundamental forces.
Electron capture is the primary <a href="/facts/Decay_mode/Ya6FVjt4">decay mode</a> for <a href="/facts/Isotope/KD9B1y6o">isotopes</a> with a relative superabundance of <a href="/facts/Proton/clCjepXP">protons</a> in the <a href="/facts/Atomic_nucleus/orpIm5Xl">nucleus</a>, but with insufficient energy difference between the isotope and its prospective daughter (the <a href="/facts/Isobar_(nuclide)/25ezJVsq">isobar</a> with one less <a href="/facts/Atomic_number/bgAr581S">positive charge</a>) for the nuclide to decay by emitting a <a href="/facts/Positron/HgV4zBzA">positron</a>. Electron capture is always an alternative decay mode for <a href="/facts/Radioactive/Ya6FVjt4">radioactive</a> isotopes that do have sufficient energy to decay by <a href="/facts/Positron_emission/psWp4bJT">positron emission</a>. Electron capture is sometimes included as a type of <a href="/facts/Beta_decay/vxTBlckp">beta decay</a>, because the basic nuclear process, mediated by the weak force, is the same. In <a href="/facts/Nuclear_physics/fzQbt1aF">nuclear physics</a>, beta decay is a type of <a href="/facts/Radioactive_decay/Ya6FVjt4">radioactive decay</a> in which a <a href="/facts/Beta_particle/x8b3ttLn">beta ray</a> (fast energetic electron or positron) and a neutrino are emitted from an atomic nucleus. Electron capture is sometimes called <a href="/facts/Inverse_beta_decay/haVxNSFA">inverse beta decay</a>, though this term usually refers to the interaction of an <a href="/facts/Neutrino/yGWVfSg2">electron antineutrino</a> with a proton.
If the energy difference between the parent atom and the daughter atom is less than 1.022 <a href="/facts/MeV/YMT1fqX9">MeV</a>, positron emission is forbidden as not enough <a href="/facts/Decay_energy/g4wDGC8r">decay energy</a> is available to allow it, and thus electron capture is the sole decay mode. For example, <a href="/facts/Rubidium-83/9jc8FbaB">rubidium-83</a> (37 protons, 46 neutrons) will decay to <a href="/facts/Krypton-83/8hRKYepJ">krypton-83</a> (36 protons, 47 neutrons) solely by electron capture (the energy difference, or decay energy, is about 0.9 MeV).

Electron capture open-in-new

Electron capture