type: comparison_note | subtopic: Radioactive Decay Types
| Property | Alpha (α) Decay | Beta-minus (β^{-}) Decay | Beta-plus (β^{+}) Decay | Gamma (γ) Decay |
|---|---|---|---|---|
| Particle emitted | He-4 nucleus (^{4}_{2}He) | Electron () + antineutrino | Positron () + neutrino | High-energy photon |
| Change in A | Decreases by 4 | Unchanged | Unchanged | Unchanged |
| Change in Z | Decreases by 2 | Increases by 1 | Decreases by 1 | Unchanged |
| Nuclear process | Emission of alpha particle | n → p + + ν̄ | p → n + + ν | Nuclear de-excitation |
| Typical energy | 4–9 MeV | 0–several MeV (spectrum) | 0–several MeV (spectrum) | 0.1–10 MeV (discrete) |
| Penetrating power | Low (stopped by paper/skin) | Medium (stopped by aluminium) | Medium | High (needs Pb/concrete) |
| Ionizing power | High | Medium | Medium | Low |
| Occurs when | A/Z ratio: excess protons or heavy nuclei | N/Z too high (excess neutrons) | N/Z too low (excess protons) | After α or β decay (excited state) |
| Example | ^{238}{92}U → ^{234}{90}Th + ^{4}_{2}He | ^{14}{6}C → ^{14}{7}N + + ν̄ | ^{22}{11}Na → ^{22}{10}Ne + + ν | Excited nucleus* → ground state + γ |
| Balancing equations | =−4, =−2 | =0, =+1 | =0, =−1 | =0, =0 |
NEET Trap: Gamma decay does NOT change A or Z. Beta-plus decreases Z by 1 (not increases). Always check by conservation of A and Z.