Radioactivity

5. The number of nuclear decays per unit time, measured in Becquerel (Bq).
8. The unwanted presence of radioactive atoms on or in an object or person.
10. Using known half-lives (e.g., Carbon-14) to determine the age of ancient organic materials.
14. The spontaneous and random process by which unstable nuclei lose energy by emitting ionising radiation (alpha, beta, or gamma) to become more stable.
16. Exposure to radiation from an external source.
17. Constant, low-level radiation present in the environment from natural sources (radon gas, cosmic rays) and artificial sources (medical, nuclear testing).
18. Fast-moving electrons or positrons emitted from the nucleus. Moderately ionising, stopped by a few millimetres of aluminium.

1. The new, more stable nucleus produced after decay.
2. Radiation with enough energy to remove electrons from atoms, leaving behind positive ions (alpha, beta, or gamma).
3. Decay is not affected by external factors like temperature, pressure, or chemical bonding.
4. The time taken for the number of radioactive nuclei (or the activity) to decrease to half of its initial value.
6. A common gamma-emitting radioisotope used in medical tracers due to its appropriate half-life and ability to be detected externally.
7. High-energy, short-wavelength electromagnetic photons. Lowly ionising, high penetration (stopped by thick lead).
9. Nuclei with the same number of protons but different numbers of neutrons.
11. A device that detects ionising radiation, often used to measure count rate.
12. It is impossible to predict which specific nucleus in a sample will decay next, or when a specific nucleus will decay.
13. A helium nucleus. Highly ionising but low penetration (stopped by paper/skin).
15. The original, unstable nucleus before decay.