3.8.1.3
Alpha decay reduces A by 4 and Z by 2
Nuclear Structure & Radiation — AQA A-Level Physics
- Occurs when the nucleus has too many nucleons (too heavy to be stable).
- The strong nuclear force cannot overcome the electrostatic repulsion between protons.
- An alpha particle (⁴₂He) is ejected.
$${}^{A}_{Z}X \rightarrow {}^{A-4}_{Z-2}Y + {}^{4}_{2}\alpha$$
- $A$: nucleon number of parent
- $Z$: proton number of parent
- $X$: parent nucleus
- $Y$: daughter nucleus
- Nucleon number (A) decreases by 4. Proton number (Z) decreases by 2. Neutron number (N) decreases by 2.
- On the N-Z graph: both N and Z decrease, so the point moves diagonally down-left.