Putting it all together
All five decays side by side: how they compare, how far each kind of radiation gets, and the single set of rules behind every one of them.
How far each kind of radiation gets
Alpha is heavy, slow and has charge +2, so it pulls hard on every electron it passes and burns through its energy within a few cm of air. Beta particles are light, with charge −1, so they get farther (a meter or so of air, a few mm of metal). Gamma rays have no charge, so they only lose energy when they happen to hit something directly. They're never fully stopped, only thinned out: about 1 cm of lead halves a beam of 1 MeV gammas. One catch: an alpha source inside the body (inhaled or swallowed) is the most damaging of all, because it dumps all its energy into a few cells.
All five on one page
| Decay | Inside the nucleus | Quark change | Force | What comes out | Change in Z, N, A | Example |
|---|---|---|---|---|---|---|
| α | 2p + 2n leave as a bundle by tunneling | none | strong + electric | helium-4 nucleus | −2, −2, −4 | U-238 → Th-234 |
| β⁻ | n → p | d → u | weak | e⁻ + ν̄ (energy shared) | +1, −1, 0 | C-14 → N-14 |
| β⁺ | p → n | u → d | weak | e⁺ + ν, then 2 × 511 keV γ | −1, +1, 0 | F-18 → O-18 |
| EC | p + e⁻ → n | u + e⁻ → d | weak | ν (fixed energy) + X-rays | −1, +1, 0 | Fe-55 → Mn-55 |
| γ | excited nucleus settles down | none | electric | a photon (fixed energy) | 0, 0, 0 | Ni-60* → Ni-60 |
Z = protons, N = neutrons, A = Z + N (mass number).
The one recipe behind all five
- A lower-energy arrangement exists. The products weigh less than the parent.
- A force provides a route there. Strong + electric for α, weak for β⁻/β⁺/EC, electric for γ.
- It happens at a random moment with a fixed chance per second (the half-life). Nothing triggers it.
- The missing mass becomes energy (E = mc²): the speed of the emitted particles plus any photons.
- Conservation rules decide which particles must appear: charge, quark count, lepton count, energy and momentum all have to balance. That's why an electron always comes with an antineutrino, and a positron with a neutrino.