Track the nucleus, not the atom.
Isotopes have the same proton number but different neutron numbers. Alpha emission removes two protons and two neutrons. Beta-minus decay converts a neutron to a proton and emits an electron and an antineutrino; gamma emission releases a photon without changing proton or mass number.
Ionising radiation can remove electrons from matter. Alpha particles are strongly ionising but have a short range; gamma radiation is more penetrating. Exposure risk depends on activity, energy, distance, shielding and whether the source is inside the body.
Alpha decay bookkeeping
Explore the relationship
Integer event counts only: each alpha emission reduces Z by 2 and A by 4. The line shows the arithmetic trend, not a decay probability.
Tap or focus a plotted point to read its values.
View plotted data as a table
| Series | Number of alpha decays | Proton number remaining |
|---|---|---|
| Proton number remaining | 0 | 88 |
| Proton number remaining | 0.0666667 | 87.8667 |
| Proton number remaining | 0.133333 | 87.7333 |
| Proton number remaining | 0.2 | 87.6 |
| Proton number remaining | 0.266667 | 87.4667 |
| Proton number remaining | 0.333333 | 87.3333 |
| Proton number remaining | 0.4 | 87.2 |
| Proton number remaining | 0.466667 | 87.0667 |
| Proton number remaining | 0.533333 | 86.9333 |
| Proton number remaining | 0.6 | 86.8 |
| Proton number remaining | 0.666667 | 86.6667 |
| Proton number remaining | 0.733333 | 86.5333 |
| Proton number remaining | 0.8 | 86.4 |
| Proton number remaining | 0.866667 | 86.2667 |
| Proton number remaining | 0.933333 | 86.1333 |
| Proton number remaining | 1 | 86 |
| Proton number remaining | 1.06667 | 85.8667 |
| Proton number remaining | 1.13333 | 85.7333 |
| Proton number remaining | 1.2 | 85.6 |
| Proton number remaining | 1.26667 | 85.4667 |
| Proton number remaining | 1.33333 | 85.3333 |
| Proton number remaining | 1.4 | 85.2 |
| Proton number remaining | 1.46667 | 85.0667 |
| Proton number remaining | 1.53333 | 84.9333 |
| Proton number remaining | 1.6 | 84.8 |
| Proton number remaining | 1.66667 | 84.6667 |
| Proton number remaining | 1.73333 | 84.5333 |
| Proton number remaining | 1.8 | 84.4 |
| Proton number remaining | 1.86667 | 84.2667 |
| Proton number remaining | 1.93333 | 84.1333 |
| Proton number remaining | 2 | 84 |
| Proton number remaining | 2.06667 | 83.8667 |
| Proton number remaining | 2.13333 | 83.7333 |
| Proton number remaining | 2.2 | 83.6 |
| Proton number remaining | 2.26667 | 83.4667 |
| Proton number remaining | 2.33333 | 83.3333 |
| Proton number remaining | 2.4 | 83.2 |
| Proton number remaining | 2.46667 | 83.0667 |
| Proton number remaining | 2.53333 | 82.9333 |
| Proton number remaining | 2.6 | 82.8 |
| Proton number remaining | 2.66667 | 82.6667 |
| Proton number remaining | 2.73333 | 82.5333 |
| Proton number remaining | 2.8 | 82.4 |
| Proton number remaining | 2.86667 | 82.2667 |
| Proton number remaining | 2.93333 | 82.1333 |
| Proton number remaining | 3 | 82 |
| Proton number remaining | 3.06667 | 81.8667 |
| Proton number remaining | 3.13333 | 81.7333 |
| Proton number remaining | 3.2 | 81.6 |
| Proton number remaining | 3.26667 | 81.4667 |
| Proton number remaining | 3.33333 | 81.3333 |
| Proton number remaining | 3.4 | 81.2 |
| Proton number remaining | 3.46667 | 81.0667 |
| Proton number remaining | 3.53333 | 80.9333 |
| Proton number remaining | 3.6 | 80.8 |
| Proton number remaining | 3.66667 | 80.6667 |
| Proton number remaining | 3.73333 | 80.5333 |
| Proton number remaining | 3.8 | 80.4 |
| Proton number remaining | 3.86667 | 80.2667 |
| Proton number remaining | 3.93333 | 80.1333 |
| Proton number remaining | 4 | 80 |
Explore: Change the initial proton number and track the two-proton decrease for each alpha decay.
Identify the daughter numbers after alpha decay of a nucleus with A = 226 and Z = 88.
- Subtract 4 from A and 2 from Z.
- The daughter has A = 222 and Z = 86.
Assumed knowledge
Atomic number and mass number.
Learning checkpoints & source
YOUR LEARNING CHECKPOINT- Balance alpha, beta and gamma changes.
- Distinguish penetration and ionisation.