Imagine a busy train station where some trains (atoms) are unstable and decide to change their form. They do this by throwing off particles or energy to become more stable. This process is called radioactive decay and is written with nuclide notation:
Nuclide notation shows the element, its mass number (A), and its atomic number (Z). For example, \$^{226}\text{Ra}\$ means radium with 226 nucleons (protons + neutrons) and 88 protons.
Think of an alpha particle as a tiny, heavy “ball” that the nucleus throws out. It’s actually a helium nucleus: 2 protons + 2 neutrons.
Decay equation example:
\$^{226}\text{Ra} \;\xrightarrow{\;\alpha\;}\; ^{222}\text{Rn} + \alpha\$
Beta decay is like a “switch” inside the nucleus: a neutron turns into a proton, emitting an electron (β⁻) or a positron (β⁺).
Two common types:
Example (β⁻):
\$^{14}\text{C} \;\xrightarrow{\;\beta^-\;}\; ^{14}\text{N} + \beta^- + \bar{\nu}_e\$
Example (β⁺):
\$^{11}\text{C} \;\xrightarrow{\;\beta^+\;}\; ^{11}\text{B} + \beta^+ + \nu_e\$
Notice how the mass number stays the same but the atomic number changes by ±1.
Gamma rays are like the “after‑party” of the nucleus: a highly excited nucleus releases excess energy as a high‑energy photon.
Decay equation (no change in A or Z):
\$^{60}\text{Co}^* \;\xrightarrow{\;\gamma\;}\; ^{60}\text{Co}\$
Because it’s just energy, gamma decay is often accompanied by α or β decay.
| Parent Nuclide | Decay Mode | Daughter Nuclide |
|---|---|---|
| \$^{238}\text{U}\$ | α | \$^{234}\text{Th}\$ |
| \$^{234}\text{Th}\$ | α | \$^{230}\text{Pa}\$ |
| \$^{230}\text{Pa}\$ | β⁻ | \$^{230}\text{U}\$ |
Each step follows the same rules: A changes by 4 for α, stays same for β, and stays same for γ. Z changes by ±2 for α, ±1 for β, and stays same for γ.