Electromagnetic radiation can damage tissue
Definition
Ionising radiation
Radiation with enough energy per photon to remove electrons from atoms or molecules, producing ions.
- The risk from electromagnetic radiation depends on frequency, intensity, exposure time and which tissue absorbs the energy.
- Higher-frequency ultraviolet, X-rays and gamma rays can damage cells because their photons carry more energy.
- Microwaves and infrared are non-ionising, but intense exposure can transfer enough energy to heat tissue.
Different regions cause different harm
- Microwaves penetrate into body tissue and can cause internal heating when their energy is absorbed by water molecules.
- Infrared radiation is absorbed mainly near the skin surface and can cause skin burns and eye damage at high intensity.
- Ultraviolet radiation can damage surface cells and DNA, causing sunburn, premature skin ageing, eye damage and an increased risk of skin cancer.
- X-rays and gamma rays can ionise molecules inside cells, damage DNA, cause mutations, kill cells or increase cancer risk.
- Gamma radiation is very penetrating, so an external source can expose tissue deep inside the body.
Protection reduces dose
Definition
Radiation dose
A measure of the energy deposited by radiation in body tissue, adjusted where necessary for the radiation's biological effect.
- Reduce exposure time, increase distance from a source and use suitable shielding.
- Use sunscreen, covering clothing and shade to reduce ultraviolet exposure.
- Use lead or thick concrete around X-ray and gamma sources, with remote handling and monitoring badges where appropriate.
- Keep microwave ovens and other sources properly shielded and never bypass safety interlocks.
Example
Comparing two hazards
- Infrared from a heater is absorbed mainly at the skin and can cause surface burns.
- Microwaves can penetrate farther before absorption and may heat tissue below the surface.
- Neither is ionising, so the harm in these examples comes from energy transfer and heating rather than direct ionisation.
Common Mistake
Do not call microwaves ionising radiation; explain microwave harm through internal heating and explain ultraviolet, X-ray and gamma harm through cell or DNA damage.
Exam technique
Name the radiation and mechanism
- State the region of the electromagnetic spectrum.
- Describe what the radiation does to tissue, such as heating or ionising molecules.
- Link the tissue change to the harm, such as burns, mutation or cancer.
Self review
- How can microwaves harm body tissue?
- Why can infrared cause burns?
- How can ultraviolet increase skin-cancer risk?
- Why are X-rays and gamma rays ionising?
- What three general methods reduce exposure?
