this form of beta decay, a proton is transformed into a neutron and a positron,
(the electron’s antiparticle), plus another particle, the electron-neutrino, ve,
which are then both ejected from the nucleus. An example of a positron emitter is
fluorine-17.
Electron Capture Another way in which a nucleus can increase its neutron-to-
proton ratio is to capture an orbiting electron and then cause the transformation of a
proton into a neutron. Beryllium-7 undergoes this process.
In each of the decay processes defined above, the daughter was a different element
than the parent. Radon becomes polonium as a result of α decay, carbon becomes
nitrogen as a result of β− decay, fluorine becomes oxygen from β+ decay, and
beryllium becomes lithium from electron capture. By contrast, gamma decay does
not alter the identity of the nucleus; it just allows the nucleus to relax and shed
energy. Imagine that potassium-42 undergoes β− decay to form calcium-42.
The asterisk indicates that the daughter calcium nucleus is left in a high-energy,
excited state. For this excited nucleus to drop to its ground state, it must emit a
photon of energy, a gamma ray, symbolized by γ.
Let’s sum up the three types of radiation: