Hazards and Uses of RadioactivityAQA GCSE Physics: Revision notes

Ionising radiation can remove electrons from atoms, creating ions that damage living tissue. The three main types of radiation have different ionising abilities:

Alpha particles are slow-moving helium nuclei with a +2 charge. They are stopped by paper or skin but cause severe damage if the source enters the body (inhalation or ingestion).

Beta particles are fast-moving electrons. They penetrate further than alpha and can penetrate thin metal, but are stopped by several millimetres of aluminium. They cause skin damage and internal harm.

Gamma rays are electromagnetic waves with no mass or charge. They penetrate deeply through most materials and require thick lead or concrete shielding. They pose the greatest hazard during external exposure to distant sources.

The ionising property is the ability to knock electrons from atoms. Alpha has the highest charge density (most ionising per unit distance), but gamma's penetration means it delivers dose over a larger area of tissue.

Safety procedures minimise exposure to ionising radiation. The key principles are based on time, distance, and shielding:

Time: Limit the duration of exposure. Workers should spend the minimum necessary time handling radioactive sources.

Distance: Increase distance from the source. Radiation intensity decreases with distance (inverse square law), so even small increases in distance significantly reduce dose.

Shielding: Use appropriate barriers:

• Alpha sources: Paper, plastic, or gloves (minimal shielding needed)
• Beta sources: A few millimetres of aluminium or plastic
• Gamma sources: Several centimetres of lead or concrete (most demanding)

Practical safety measures in the laboratory:

1. Never touch radioactive sources directly; use tongs or forceps
2. Wear protective clothing (lab coat, gloves) to prevent contamination
3. Use lead-lined boxes or containers for storage
4. Keep sources in shielded containers when not in use
5. Wash hands thoroughly after handling
6. Never eat, drink, or apply cosmetics in areas with radioactive sources
7. Use fume hoods or designated areas with controlled ventilation
8. Follow strict protocols for disposal of radioactive waste
9. Monitor exposure using film badges or dosimeters to track accumulated dose
10. Train all personnel and maintain clear warning labels and signs

Personal protective equipment (PPE) includes lead aprons (especially for gamma work), lead gloves, and eye protection. Different radiation types require different approaches: alpha is primarily an inhalation/ingestion risk (control via equipment and technique), while gamma requires heavy shielding.

Radioactive isotopes have valuable practical uses because their radiation can be detected, tracked, or used to kill cells:

Medical Uses:

Medical tracers (diagnostic imaging): Radioactive isotopes are injected, ingested, or inhaled, then tracked using detectors as they move through the body. Doctors map blood flow, organ function, and locate disease. Example: Technetium-99m (half-life ~6 hours) is used to image the heart, lungs, and bones. The short half-life means the patient receives a defined dose that decays quickly.

Cancer treatment (radiotherapy): Gamma radiation from Cobalt-60 is directed at tumours to kill cancer cells. The radiation damages DNA, preventing cell division. Alternatively, radioactive isotopes like Iodine-131 are given internally to patients with thyroid cancer; the thyroid selectively absorbs iodine, concentrating the radiation at the tumour site.

Industrial and domestic uses:

Sterilisation: Gamma rays (from Cobalt-60 or Caesium-137) kill bacteria and viruses on medical equipment, food, and pharmaceuticals without leaving radioactive residue. The high-energy gamma passes through sealed packages, sterilising contents.

Smoke detectors: Contain Americium-241 (alpha emitter). Alpha particles ionise air between two electrodes, allowing current to flow. Smoke absorbs alpha particles, breaking the circuit and triggering the alarm.

Thickness gauges (industrial): Beta or gamma sources measure material thickness (paper, plastic, metal). As material thickness increases, less radiation reaches the detector, allowing calculation of thickness. Continuous non-contact monitoring without damaging the product.

The choice of radioactive isotope depends on balancing emission type (alpha, beta, or gamma), half-life, and the application requirements:

Emission type selection:

• Gamma: Used when penetration is needed (radiotherapy, sterilisation, medical imaging). Penetrates tissue and materials; can be directed or detected externally.
• Beta: Used in industrial gauges where moderate penetration is needed; also suitable if internal damage is desired (cancer treatment with Iodine-131).
• Alpha: Used only in sealed applications (smoke detectors) where the source cannot be inhaled or ingested; high ionising power damages cells but doesn't penetrate packaging.

Half-life selection:

Key principle: Isotopes must be long-lived enough to be useful but short-lived enough to minimise risk.

Examples of selection logic:

1. Technetium-99m for heart imaging: Gamma emission allows external detection; 6-hour half-life means it decays within one day, limiting patient dose.
2. Cobalt-60 for sterilisation: Very penetrating gamma; 5-year half-life means one source sterilises millions of packages over years.
3. Iodine-131 for thyroid cancer: Beta emitter concentrates naturally in thyroid tissue; 8-day half-life allows treatment then decay without long-term body burden.
4. Americium-241 in smoke detectors: Alpha particle ionises air but cannot escape sealed casing; 432-year half-life acceptable because source is sealed and never in contact with user.

Irradiation and contamination are distinct hazards that require different safety approaches:

Irradiation:

• Exposure to radiation from an external source (or an internal source where the radiation itself enters the body, not the source).
• The radioactive material remains outside the body or is not present in the body at all.
• Example: standing near a gamma source, or a patient receiving a dose of X-rays.
• Effect: Ionising radiation passes through tissue, removing electrons and damaging cells (burns, mutations, cancer risk).
• Time-dependent: Once the source is removed, irradiation stops immediately (no continuing dose).
• Duration: Dose depends on exposure time and distance from source.

Contamination:

• Presence of unwanted radioactive material on the skin, clothing, equipment, or inside the body (ingestion, inhalation, or absorption through a wound).
• The radioactive source itself is in contact with or inside the body.
• Example: radioactive dust on a surface, or swallowing a radioactive particle.
• Effect: The source continuously emits radiation from within or on the body. Additionally, the material may be concentrated in specific organs (e.g., iodine in thyroid), causing very high local doses.
• Persistent: The contamination continues to irradiate the body until the radioactive material is removed or decays away (depends on half-life).
• Hazard: Much more serious because the source remains in place, delivering continuous dose, and chemical/biological uptake concentrates radiation in specific tissues.

Effects on living tissue:

Immediate effects (acute radiation syndrome):

• High doses (>1 Gy) cause nausea, vomiting, diarrhoea, hair loss, and damage to bone marrow (immune system collapse).
• Skin burns from high-dose external exposure.

Delayed effects:

• Cancer: Ionising radiation damages DNA. If damage is not repaired, mutations can cause malignant growth (leukaemia, solid tumours) appearing months or years later.
• Genetic damage: Damage to reproductive cells can cause hereditary conditions in offspring.
• Cataracts: Radiation damage to eye lens proteins causes clouding.

Prevention of contamination:

1. Use tongs or forceps (never touch directly).
2. Prevent ingestion (no eating/drinking in lab) and inhalation (use fume hoods).
3. Wash hands and decontaminate equipment.
4. Isolate and contain spills.
5. Wear protective clothing to prevent material reaching skin.