K Capture
Definition and meaning of K Capture in chemistry.
K capture is a type of radioactive decay in which an atomic nucleus captures an inner-shell electron (typically from the K shell), and the electron combines with a proton to produce a neutron and emit an electron neutrino.
In more detail
K capture occurs when a proton-rich nucleus achieves greater stability by absorbing an orbital electron from the atom, usually from the K shell (the innermost electron orbital). The captured electron merges with a proton in the nucleus to form a neutron, while an electron neutrino (νₑ) is simultaneously emitted to conserve lepton number and energy. This process decreases the nucleus's atomic number by one while keeping the mass number constant, since a proton (charge +1, mass ~1) is converted into a neutron (charge 0, mass ~1). K capture is named after the K shell because electrons are most frequently captured from this innermost shell, though capture from higher shells can occur less commonly.
Key facts
| Field | Physical Chemistry |
|---|---|
| Also called | Electron capture (EC), orbital electron capture |
| Nuclear change | Atomic number decreases by 1; mass number unchanged |
| Emitted particle | Electron neutrino (νₑ) |
Beryllium-7 undergoes K capture to form stable lithium-7: ⁷Be + e⁻ → ⁷Li + νₑ. This decay has a half-life of 53 days and is commonly observed in solar fusion processes.
Frequently asked questions
Why is it called K capture?
The K shell is the innermost electron orbital around the nucleus. Although electrons from higher shells can sometimes be captured, the process is named after the K shell because capture from this shell is most probable.
How does K capture differ from beta-minus decay?
In K capture, an orbital electron is absorbed into the nucleus where it combines with a proton. In beta-minus decay, a neutron in the nucleus decays into a proton, emitting an electron and antineutrino. Both decrease atomic number by one, but they involve opposite processes.