GCSE Physics resources
AQA GCSE Atomic structure
A sealed source outside the body and radioactive material inside the body require different controls. Both can cause irradiation, but only one involves contamination.
Subsection scope: Contamination and irradiation: both courses, both tiers. Background/dose, lifetime hazards and medical uses: Physics only, both tiers.
Start here
A sealed source outside the body and radioactive material inside the body require different controls. Both can cause irradiation, but only one involves contamination.
Before you revise
Choose an answer from memory. Your result tells you what to watch for in the guide.
Core revision guide
A sealed source outside the body and radioactive material inside the body require different controls. Both can cause irradiation, but only one involves contamination.
Scope: 8463 and 8464 · Foundation and Higher
Irradiation means radiation reaches an object. Contamination means radioactive material is on or inside it; the material keeps emitting until removed or decayed. A normal medical X-ray exposure irradiates tissue without leaving radioactive material behind. Removing an external source stops that irradiation; contaminated material may continue exposing tissue from nearby.
Scope: 8463 and 8464 · Foundation and Higher
Ionisation removes electrons from atoms and can damage biological molecules/DNA, causing cell death or mutations. External dose can be reduced by shorter exposure, greater distance and suitable shielding. Unsealed material also needs containment, gloves, contamination monitoring and measures preventing ingestion/inhalation. Alpha outside intact skin is readily absorbed; internal alpha contamination is hazardous because it strongly ionises nearby tissue.
Scope: 8463 and 8464 · Foundation and Higher
Risk depends on radiation type, dose, source location and duration. A useful medical procedure may justify controlled exposure when the benefit outweighs risk; it is not automatically risk-free. School demonstrations use approved sealed sources under trained staff procedures, with remote handling and secure storage.
Scope: 8463 Physics only · Foundation and Higher
Background radiation is present continually. Natural sources include radioactive rocks and radon from the ground, and cosmic rays from space. Man-made contributions include fallout from nuclear testing or accidents. Occupation and location change exposure: a flight crew may receive more cosmic radiation, and local geology can change radon levels. Dose data use sieverts, with 1000 mSv = 1 Sv; the unit will be supplied rather than required from recall. Compare like time intervals and add supplied contributions. For example, an annual 1.8 mSv natural contribution plus 0.2 mSv man-made contribution gives 2.0 mSv = 0.0020 Sv. A dose value alone does not identify the source or prove that no risk exists.
Scope: 8463 Physics only · Foundation and Higher
State what is being held equal. For the same initial number of nuclei of the same radiation type, a shorter half-life gives a higher initial activity: more decays occur per second. Its activity then falls sooner. A long-lived contaminant can remain a source for much longer, requiring long-term control. For sources adjusted to the same initial activity, the short-lived one falls sooner without necessarily starting at a larger activity. Hazard also depends on emitted radiation, dose, location and whether material enters the body. Neither “shorter is always safer” nor “longer is always safer” is a valid rule.
Scope: 8463 Physics only · Foundation and Higher
A tracer introduced into the body can emit penetrating gamma radiation detected outside it, showing the function or location of an organ. Choose a lifetime long enough for the investigation but short enough to limit continuing exposure; a lifetime much shorter than the procedure may leave an unusable signal. Radiotherapy uses ionising radiation to damage or destroy unwanted tissue. Exposure is planned to give the required effect while limiting healthy-tissue dose. Compare the expected benefit with supplied dose and consequence data; both methods carry risks. Do not treat a tracer choice as a universal clinical protocol or assume that a lower dose always gives enough diagnostic information.
Misconception clinic
Read each belief, say what is wrong with it, then compare your correction.
Tempting idea: Irradiation only; the glove contains no source.
Use instead: The powder itself is present. The glove can now carry a source and spread it.
Tempting idea: Alpha passes freely through the whole body.
Use instead: Its range is short. Short range concentrates damage near an internal source.
Retrieval practice
Worked examples
Apply distinguish exposure from material transfer in the worked reasoning, then try the changed-context questions below.
Scope: 8463 and 8464 · Foundation and Higher
This is contamination because radioactive material is on the gloves and could be transferred or taken into the body.
Scope: 8463 and 8464 · Foundation and Higher
Minimise time near the source and maximise distance; thick shielding can also reduce the gamma radiation reaching the person.
Scope: 8463 and 8464 · Foundation and Higher
X-rays irradiate an object but do not leave radioactive material behind, so the object does not become radioactive in normal use.
Exam precision
Do this: Name the exposure route and a control that interrupts it. For supplied medical data, weigh signal duration, dose and benefit before making a qualified choice.
Independent practice
Write an answer before opening the marking guidance. Then edit the exact phrase or step that would gain the next mark.
Scope: 8463 and 8464 · Foundation and Higher
Original PhysicsUK mark scheme: Point 1 (1 mark): Irradiation is exposure to radiation; contamination is radioactive material on/in an object. Point 2 (1 mark): A suitable irradiation control: reduce time, increase distance or use appropriate shielding. Point 3 (1 mark): A suitable contamination control: contain unsealed material/prevent inhalation, ingestion or spread. Award each distinct point once. Accept equivalent scientifically correct wording. No half marks.
Model answer: Irradiation is exposure and can be reduced by distance or shielding. Contamination is the presence of radioactive material and needs containment and prevention of spread/entry to the body.
Scope: 8463 and 8464 · Foundation and Higher
Original PhysicsUK mark scheme: Point 1 (1 mark): The X-ray source was external and leaves no radioactive material in ordinary diagnostic use. Point 2 (1 mark): Contamination leaves an emitting source on/in the person, so it continues until removed or decayed. Award each distinct point once. Accept equivalent scientifically correct wording. No half marks.
Model answer: Normal X-rays leave no radioactive material behind. A contaminated person retains a source that continues irradiating nearby tissue.
Scope: 8463 Physics only · Foundation and Higher
Original PhysicsUK mark scheme: Point 1 (1 mark): Total = 1.4 + 0.4 + 0.2 = 2.0 mSv. Point 2 (1 mark): 2.0 mSv = 0.0020 Sv. Point 3 (1 mark): A pilot’s occupation can increase cosmic-ray exposure at altitude (accept another justified supplied-location/occupation change). Award each distinct point once. Accept equivalent scientifically correct wording. No half marks.
Model answer: The total is 2.0 mSv, or 2.0/1000 = 0.0020 Sv. A pilot may receive a greater cosmic contribution because of time at altitude, so occupation can change the total.
Scope: 8463 Physics only · Foundation and Higher
Original PhysicsUK mark scheme: Point 1 (1 mark): Recommend B because it gives detectable gamma radiation throughout the required hour. Point 2 (1 mark): Gamma can leave the body and be detected to explore organ function/location. Point 3 (1 mark): B persists longer and has the larger supplied dose, so its benefit must justify added exposure/healthy-tissue risk. Point 4 (1 mark): A’s lower dose is insufficient reason to choose it because the stated signal fails; neither half-life alone proves universal safety. Award each distinct point once. Accept equivalent scientifically correct wording. No half marks.
Model answer: Choose B: its gamma emission can be detected outside the body throughout the one-hour investigation. A has a lower supplied dose but loses usable signal before completion. B’s longer persistence and 0.3 mSv dose increase continuing exposure, so the diagnostic benefit must justify the risk to healthy tissue. A shorter half-life is not automatically the safer useful choice.
Questions pupils ask
Exposure alone does not mean radioactive material has been transferred. Contamination specifically means such material is on or inside the object.
Useful next steps