Background radiation, hazards and uses

We are constantly bathed in low-level background radiation from many sources. Some radioactive isotopes are also intentionally used in medicine and industry.

Sources of background radiation

• Natural — cosmic rays: high-energy particles from space.
• Natural — radon: radioactive gas from uranium in granite rocks. Higher levels in Cornwall.
• Natural — food and drink: bananas (potassium-40), Brazil nuts.
• Medical: X-rays, CT scans, radiotherapy.
• Nuclear accidents and weapons: small but globally distributed (e.g. Chernobyl).

A typical UK person receives ~2.7 mSv/year of background dose.

Risks

Ionising radiation can:

• Damage DNA → mutations → cancer.
• Kill cells (high doses) → tissue damage.
• Affect developing fetuses.

Risk depends on dose, dose rate, and the type of radiation. The dose unit is the sievert (Sv) — typical safe annual limit ~20 mSv for nuclear workers.

Medical uses

Diagnosis (low dose, often gamma)

• Tracers — drink or inject a short-half-life isotope (e.g. technetium-99m). A gamma camera tracks where it concentrates, showing organ function.
• PET scans — use positron-emitting isotopes.

Therapy (high dose, often gamma)

• Radiotherapy — focus high-dose gamma rays on tumours from outside, or implant beta-emitters near them. Aim: kill cancer cells while sparing healthy tissue.

Imaging

• X-rays — moderate-dose snapshots of bones and dense structures.

Industrial uses

• Sterilising medical instruments with γ — kills microbes without heat.
• Food preservation by γ irradiation.
• Smoke detectors — americium-241 emits α; smoke disrupts the ionised air, triggering alarm.
• Thickness gauges — β-source above moving paper; less β passes if paper is too thick.

Risk vs benefit

For diagnostic tests, the small risk from radiation is far outweighed by the benefit of detecting illness. For therapy, the alternative is often worse (untreated cancer). Doctors aim to keep doses as low as reasonably achievable (ALARA).