7.10 - Why Radiation Is Harmful

How ionising radiation damages living cells

• Ionising radiation enters living cells and ionises the atoms and molecules inside them.
• Removing electrons damages or destroys these molecules, which damages the cell.
• The amount of harm depends on the radiation dose.

Lower dose - Mutation and cancer

• A lower dose tends to cause minor damage without killing the cell.
• This damage can mutate the cell's DNA.
• A mutated cell may divide uncontrollably, leading to cancer.

Higher dose - Radiation sickness

• A higher dose kills cells outright.
• Killing a large number of cells at once causes radiation sickness, with symptoms such as vomiting, tiredness and hair loss.
• Very high doses can be fatal.

Ionising power

• The more ionising the radiation, the more damage it causes to cells.
• Most to least ionising: alpha → beta → gamma.

Radiation hazards inside and outside the body

How dangerous a radioactive source is depends on the type of radiation and whether the source is outside the body (irradiation) or inside it (contamination).

Outside the body (irradiation)

• Beta and gamma are the most dangerous because they can penetrate the skin and reach internal organs.
• Alpha is the least dangerous because it can't penetrate the outer layer of skin and is stopped by a few centimetres of air.

Inside the body (contamination)

• Alpha is the most dangerous because it is the most strongly ionising and all of its energy is absorbed in a small, concentrated area of tissue.
• Beta is less dangerous because its energy is spread over a wider area, and some passes out of the body.
• Gamma is the least dangerous because it is weakly ionising and most of it passes straight out of the body without being absorbed.