MYP frequently asks you to compare the three types of radiation in a table. Know:

| Radiation | Nature | Charge | Penetration | Ionising ability |

|-----------|--------|--------|-------------|------------------|

| Alpha ($\alpha$) | Helium nucleus $^4_2He$ | +2 | Stopped by paper/skin | Highly ionising |

| Beta ($\beta^-$) | Fast electron $^0_{-1}e$ | -1 | Stopped by ~3 mm aluminium | Medium |

| Gamma ($\gamma$) | EM wave | 0 | Reduced by thick lead/concrete | Low |

Nuclear equations must balance mass number (top) and atomic number (bottom). e.g., $^{238}_{92}U \rightarrow ^{234}_{90}Th + ^4_2He$.

Half‑life appears in both graphical and numerical form. From a graph showing activity (or count rate) vs time:

Step‑by‑step half‑life problems:

- After 1 half‑life: amount = initial / 2

- After 2 half‑lives: amount = initial / 4, etc.

- Number of half‑lives = total time / half‑life.

Typical question: “A sample has a half‑life of 5 years. How much of a 100 g sample remains after 15 years?” → 15/5 = 3 half‑lives, remaining mass = 100 / 2³ = 12.5 g.