Radioactivity Study Guide

Radioactivity involves the spontaneous emission of radiation (alpha, beta, or gamma) from unstable atomic nuclei. This property makes radioactive isotopes, or radioisotopes, useful in a variety of applications across different fields. In household smoke alarms, a small amount of an alpha-emitting radioisotope ionises the air, allowing a current to flow. Smoke disrupts this ionisation, triggering the alarm. For food irradiation, gamma rays are used to kill bacteria, parasites, and insects, extending shelf life and reducing the risk of foodborne illnesses without making the food radioactive. Sterilisation of medical equipment, particularly heat-sensitive items, also uses gamma radiation to destroy microorganisms. Industrial applications include tracing, where a radioisotope is added to a fluid to detect leaks in pipes or monitor flow, and gauging thickness, where the absorption of radiation varies with material thickness, allowing for precise measurement without contact. In medicine, targeted radioisotopes are used for diagnosing certain conditions by tracking their movement through the body, and for treating cancers by directing radiation to destroy malignant cells.

Ionising radiation carries significant risks due to its ability to disrupt atoms and molecules within living tissue. This disruption can directly damage cells, leading to symptoms like radiation sickness from high doses, or potentially causing more subtle, long-term effects. A key danger is the damage to DNA molecules, the body's genetic material. When DNA is damaged, it can result in mutations. These mutations might lead to the uncontrolled cell growth characteristic of cancer, which can develop years after exposure. To mitigate these dangers, strict precautions are necessary. These include minimising exposure time, increasing distance from the source, and using appropriate shielding materials. Limiting exposure time reduces the total amount of radiation absorbed. Maximising distance exploits the inverse square law, where radiation intensity decreases rapidly with distance. Shielding, such as lead or concrete, absorbs radiation, preventing it from reaching living tissue. Additionally, monitoring devices like dosimeters help track exposure levels for individuals working with radiation sources. These measures aim to keep radiation exposure as low as reasonably achievable (ALARA).