Each type of decay is characterized by changes within the decaying isotope's nucleus.
|
Decay
|
Change within the nucleus |
Net result |
|
Alpha
|
An alpha particle is ejected from the nucleus.
|
The mass of the isotope decreases by 4 amu and the atomic number decreases by 2 amu. |
| Gamma
|
An excited nucleus emits a high energy photon. |
Radio decay processes can create 'new' nuclei in which nucleons are in excited states (above ground states). When they relax toward the ground state, energy is emitted as photons. These photons are called gamma rays. |
|
Beta
|
An electron (negatron, usually referred to as a beta particle) is ejected from the nucleus when a neutron spontaneously decays into a proton. An antineutrino also is emitted.
|
The mass of the isotope decreases very slightly, but the atomic number increases by 1 unit. |
Beta
(positron)
|
A positron is ejected from the nucleus when a proton becomes a neutron. A neutrino also is emitted. |
The mass of the isotope decreases slightly, and the atomic number decreases by 1 unit. (Separated neutrons are more massive than protons. The point is that the nuclear entity, as a whole, experiences a mass decrease.) |
Beta
(Electron Capture)
EC
|
An electron is captured by a nucleus to convert a proton into a neutron. A neutrino is emitted. |
The mass of the isotope decreases slightly, and the atomic number decreases by 1 unit. (Separated neutrons are more massive than protons. The point is that the nuclear entity, as a whole, experiences a mass decrease.) |
Negatron emission, positron emission, and electron capture result from the weak interaction, illustrated [local] in terms of the standard model.
Imagine (an unstable, pulsating) nuclear broth of protons and neutrons moving incessantly. If, for an instant, two protons and two neutrons come together as a potential helium nucleus (very stable), then they may pull together and -- once slightly 'separated' from the broth, be pushed away due to the repulsions of the positive electric charges. Alpha decay results when the strong interaction forms a helium nucleus to an extent that the electrical force can then push the two residual pieces (alpha particle, daughter nucleus) apart. If the pulsating broth model is a bit clunky for your tastes, check out a well-illustrated quantum mecahanical tunneling [local] model.
The mechanism for gamma radiation follows more closely the mechanism for emitting photons from an atom or molecule to lower an electronic, vibrational, or rotation energy level.
