Uses & Dangers of RadiationEdexcel GCSE Physics: Revision notes

Background radiation is the low-level ionising radiation present in the environment at all times. Its main origins are:

• From the Earth: radioactive rocks and soil (e.g. radon gas), building materials, and medical procedures
• From space: cosmic rays

Background radiation must be measured and subtracted from readings in experiments to find the activity due to a source alone.

Two methods are commonly used:

• Photographic film: darkens on exposure to ionising radiation; the amount of darkening indicates the dose received (used in film badges worn by radiation workers)
• Geiger–Müller (GM) tube: connected to a counter, it detects individual ionising particles/rays passing through it, giving a count rate that indicates activity

• Household smoke alarms — a weak alpha source ionises air between two plates; smoke disrupts the current, triggering the alarm
• Irradiating food and sterilising equipment — gamma radiation kills bacteria/microorganisms without making the item radioactive
• Tracing and gauging thicknesses — radioactive tracers follow flow (e.g. in pipes); beta sources monitor material thickness by measuring transmitted radiation
• Diagnosis and treatment of cancer — radioactive tracers and targeted radiotherapy

PET scanners use short-lived radioactive tracers that emit positrons; these annihilate with electrons in the body, producing gamma rays that are detected to build an image of internal processes. Because these isotopes have very short half-lives, they must be produced near to where the scan takes place, as they would decay away before reaching a patient from a distant facility.

Ionising radiation can damage living tissue, causing burns, and can cause mutations in DNA which may lead to cancer. Precautions depend on the type and half-life of the radiation:

• Sources with a long half-life remain dangerous for a long time, so need long-term safe storage/shielding
• Sources with a short half-life are intensely active for a short period, so need care handling immediately but decay away quickly

Safety precautions include: minimising exposure time, maximising distance from sources, using shielding (lead/concrete), and limiting the radiation dose given to patients. Medical personnel are protected using lead aprons, shielding, and by standing behind screens or leaving the room during exposure.

• Contamination: unwanted radioactive material (particles) getting onto or into an object/person (e.g. on skin, or ingested/inhaled) — the source stays with the person, continuing to expose them even after the original exposure event
• Irradiation: exposure to radiation from a source outside the body, without the source itself remaining in contact — once removed from the source, exposure stops

Contamination is generally more hazardous long-term because the radioactive material remains in/on the body. Irradiation risk stops as soon as the person leaves the radiation field.

Treating tumours: radiation can be applied externally (a beam aimed at the tumour from outside the body, like irradiation) or internally (a radioactive source placed inside/near the tumour, like localised contamination) — internal treatment can deliver a more concentrated dose to the tumour with less damage to surrounding tissue, but carries handling/removal risks.