The three types of beta emission are;
- Beta-minus () decay
- Beta-plus () decay – otherwise known as positron emission
- Orbital electron capture
and emission are discussed here. Orbital electron capture is a process that can occur when the ratio of neutrons to protons is low.
In this process, instead of a proton being converted into a neutron with the emission of a positron (and electron-neutrino), a proton rich nucleus of an electrically neutral atom absorbs an electron from one of the inner electron shells (or energy levels). This process there converts a proton into a neutron;
As shown on the page focusing on and , nuclear equations need to ensure charge, baryon number and lepton number are conserved, so first lets write a quark equation;
Charge is conserved. ✓
Baryon number is conserved. ✓
Lepton number is not conserved. ✓
So an additional particle must be emitted that does not affect the charge or the baryon number but does change the lepton number. What particle has no charge, no baryon number and a lepton number of -1?
It must be a lepton and for no charge to be present the particle must be one of neutrinos – an antielectron-neutrino.
And so, the full quark transformation for orbital electron capture must be:
- Charge: ✓
- Baryon number: ✓
- Lepton number: ✓
In addition to this the full process in which a proton transforms into a neutron is:
For more information watch this YouTube clip: