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Edexcel GCSE Physics · 1PH0
Edexcel 1PH0 · 6.29 Check the specification (PDF) (opens in a new tab)
Ionising radiation transfers energy to matter. When it passes through living tissue, it can remove electrons from atoms and molecules, turning the atoms into ions. These chemical changes can disrupt important molecules and damage cells.
A damaged cell may repair itself, function incorrectly or die. If many cells are harmed, the tissue itself can be damaged. A sufficiently large dose over a short time can therefore cause serious tissue damage.
DNA carries the instructions that control a cell. Ionisation can damage DNA, and an alteration that remains in the DNA is a mutation. Some mutations have little effect, while others alter the way a cell functions.
A mutation in genes controlling cell division can allow a cell to grow and divide uncontrollably. This may eventually produce a cancerous tumour. Cancer is therefore a possible delayed effect of exposure, not a certain outcome: receiving a dose increases risk rather than guaranteeing harm.
Ionisation can lead to tissue damage or DNA mutations, while less time, greater distance and suitable shielding reduce exposure.
Radiation precautions aim to keep exposure as low as reasonably achievable. Three central precautions are time, distance and shielding.
Radioactive sources should consequently be kept behind suitable shielding when not in use, rather than left exposed. A worker may also wear a dosimeter so that their accumulated dose can be checked. The dosimeter monitors exposure; it does not stop the radiation.
A radioactive material that gets onto the skin or inside the body can continue irradiating tissue while it remains there. Sources should therefore be kept contained, and suitable protective clothing can help prevent radioactive particles reaching the skin or clothing. These controls complement time, distance and shielding by preventing the source itself from being carried with the person.
The precautions all follow from the same idea: ionising radiation can damage cells and cause mutations, so unnecessary exposure and contamination must be avoided.
Ionising radiation removes electrons from atoms. In living tissue this can:
A harmful effect is possible, not inevitable: greater exposure means greater risk.
Recall time, distance, shielding:
Keep sources contained and shielded when not in use, use handling equipment to increase distance, and prevent radioactive material reaching the body. A dosimeter monitors dose but provides no protection.
Build the causal chain explicitly: ionising radiation ionises atoms, this damages cells or DNA, DNA damage can cause mutations, and some mutations may lead to cancer.
When asked for precautions, explain how each one reduces exposure: spend less time near the source, increase distance, or place suitable shielding between the source and the person.
Do not say that exposure will definitely cause cancer. It increases the risk because mutations are possible.
A dosimeter measures accumulated dose; it does not shield its wearer from radiation.
Do not claim that all protective clothing stops gamma radiation. The shielding must suit the radiation involved.
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Last updated
Ionising radiation
Radiation energetic enough to remove electrons from atoms, producing ions.
Tissue damage
Harm to cells which can impair or destroy them and, if sufficiently widespread, damage tissue.
Mutation
A change in the genetic material of a cell.
Radiation dose
The amount of ionising radiation received, considered in relation to its potential to cause harm.
Shielding
Material placed between a radiation source and a person to reduce the radiation reaching the person.
Radioactive contamination
The unwanted presence of radioactive material on or inside an object or organism.
Dosimeter
A device worn to monitor the radiation dose received by a person.
Put your knowledge into practice — try past paper questions for Physics
Ionising radiation
Radiation energetic enough to remove electrons from atoms, producing ions.
Tissue damage
Harm to cells which can impair or destroy them and, if sufficiently widespread, damage tissue.
Mutation
A change in the genetic material of a cell.
Radiation dose
The amount of ionising radiation received, considered in relation to its potential to cause harm.
Shielding
Material placed between a radiation source and a person to reduce the radiation reaching the person.
Radioactive contamination
The unwanted presence of radioactive material on or inside an object or organism.
Dosimeter
A device worn to monitor the radiation dose received by a person.