🔬 Damage inside a cell
Ionising radiation that is absorbed in a cell ionises the atoms and molecules there. If this damages the cell's DNA, the cell may work badly or stop working.
Radioactivity » Dangers of Ionising Radiation
What you'll learn this session
Study time: 30 minutes
Edexcel spec: 7.16
- How ionising radiation damages cells and can cause mutations
- What can happen to the body after a small dose and after a large dose
- Why radioactive waste is a problem to dispose of
- How the risks from waste are reduced
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Unlock This CourseWhy ionising radiation is dangerous
Alpha particles, beta particles and gamma rays are all ionising radiations. In Alpha, Beta and Gamma Radiation you saw that they can knock electrons off atoms and turn them into ions. That is useful in a Geiger-Müller tube. Inside a living thing it is a problem, because living things are made of cells, and cells are built from atoms and molecules that can be damaged.
Key terms:
- Radiation sickness: illness caused by a large dose of radiation.
- Radioactive waste: unwanted material that contains radioactive atoms.
💥 The damage varies
A cell may die, may repair itself, or may be changed in a way that is passed on when it divides. The more radiation that is absorbed, the more cells are harmed.
Mutations and cancer
DNA is the set of instructions inside each cell. If ionisation damages it, the instructions can change. Remember from Dangers of Electromagnetic Waves, this change is a mutation.
A mutated cell can go on to divide in an uncontrolled way. That makes a lump of cells that keep growing, which is a cancer. Radiation can therefore make cells cancerous as well as killing them.
Radiation can cause mutations in any living organism, not only in people. This is why ionising radiation is a risk to animals and plants too.
Damage to cells and tissue
The size of the dose matters. A small dose damages only a few cells, and the body may be able to cope. A larger dose harms many cells at once.
| Dose | What can happen |
|---|---|
| Small dose | A few cells are damaged. Some may die. Some may become cancerous, perhaps years later. |
| Large dose | Many cells in the tissue die. This can cause burns on the skin and radiation sickness. |
The everyday precautions for handling sources (shielding, distance and time) were covered in Contamination and Irradiation.
The problem with radioactive waste
Hospitals, industry and nuclear power stations all produce radioactive waste. It cannot just be thrown away, for two reasons.
- Some of it stays radioactive for thousands of years. From Activity and Half-Life, a long half-life means the activity falls very slowly.
- It must be kept away from people and water supplies. If radioactive atoms got into drinking water, people could be contaminated.
Reducing the risks from waste
There is no way to make radioactive atoms stop decaying. The risk is reduced by locking the waste away safely for as long as it is dangerous.
| What is done | Why it helps |
|---|---|
| Seal the waste in glass, steel and concrete | The radioactive atoms are trapped, so they cannot leak out or spread. |
| Store it deep underground in stable rock | It is far from people, and stable rock does not move or crack easily, so the waste stays put and away from water supplies. |
| Use shielded containers | The shielding absorbs radiation, so people nearby are not irradiated. |
| Use remote handling when it is moved | Workers are kept at a distance, so they receive a smaller dose. |
Worked example
A hospital has a used source that will be radioactive for thousands of years. Suggest two ways of making its storage safer.
The source is radioactive for a very long time, so the waste must be kept away from people and water supplies.
One way: seal it in glass, steel and concrete so the atoms cannot leak out.
Another way: store it deep underground in stable rock, far from people.
Moving it by remote handling in a shielded container would also reduce the dose to workers.
Common mistakes
- Burns from a large dose are tissue damage caused by ionisation, not heat. The damage to cells comes from ionisation, especially of DNA.
- Saying that waste stops being dangerous if it is buried. It is still radioactive. Burying it deep in stable rock only keeps it away from people and water.
- Writing that a mutation always causes cancer. A mutation can make a cell cancerous, but cells may also die or repair the damage.
- Forgetting the word DNA. A good answer links ionisation to damage to DNA.
- Saying that the waste can be made safe by making it decay faster. Nothing we do changes how fast it decays.
Exam-style question
A power station produces radioactive waste. Some of it will stay radioactive for thousands of years.
(a) Explain how ionising radiation can cause a cell to become cancerous. [3 marks]
(b) State two other effects on the body of a large dose of radiation. [2 marks]
(c) Describe two ways in which the risks from storing this waste are reduced. [2 marks]
Model answer
(a) The radiation ionises atoms in the cell (1). This damages the DNA in the cell, which is a mutation (1). The mutated cell may divide in an uncontrolled way and become cancerous (1)
(b) Any two from: cells and tissue die (1), burns (1), radiation sickness (1)
(c) Any two from: sealed in glass, steel and concrete (1), stored deep underground in stable rock (1), kept in shielded containers (1), moved by remote handling (1)
Exam tip
In a cancer question, write the chain in order: ionisation, damage to DNA, mutation, uncontrolled cell division. Each link can earn a mark.