Uses and hazards — OCR GCSE Physics
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Uses and hazards explained
Contamination means radioactive material gets onto or into an object, a surface or a person, so the source itself is transferred and keeps emitting inside or on the body.
Read the full explanation
Irradiation means exposure to radiation passing through from a source that stays outside the body; the person does not become radioactive. A spilled dust that settles on skin contaminates it, whereas standing near a sealed source in a beam is irradiation. Hazards differ: contamination can be inhaled or swallowed and continue delivering dose until removed, and it can spread, so protective clothing, gloves, containment and careful disposal matter. Irradiation delivers dose only while exposure lasts, so distance, shielding and limiting time reduce it. Compare both by asking whether the source moves with the person and whether the hazard persists after leaving the area.
explain why the hazards associated with radioactive material differ according to the half-life involved (content found only in the physics separate science qualification)
This content is assessed only in the physics separate science qualification, so treat it as separate-science scope even though the row is listed for both tiers. Half-life is the time for the activity of a sample to halve. A short half-life means the material decays quickly, so its activity and hazard fall rapidly, but it emits intensely while fresh and may need handling soon after production. A long half-life means activity falls slowly, so the material remains hazardous for a long time and persists in the environment. Explain the hazard by linking half-life to how long the material stays active and how intense the emission is at a given moment, using a comparison such as a short-half-life tracer versus a long-lived waste source.
describe the different uses of nuclear radiations for exploration of internal organs, and for control or destruction of unwanted tissue (content found only in the physics separate science qualification)
Nuclear radiations are used in medicine in two broad ways. For exploration of internal organs, a small amount of a gamma-emitting tracer is taken into the body and its radiation passes out through tissue to a detector, so an image shows where the tracer has collected; gamma is chosen because it penetrates tissue and leaves the body, while alpha and beta are largely absorbed before reaching a detector. For control or destruction of unwanted tissue, a targeted dose of radiation is aimed at the tissue so that its cells are damaged and stop dividing; this is how radiotherapy treats tumours. The same penetrating property that makes gamma useful for imaging also makes it useful for treatment, but the dose and targeting differ: imaging needs a tiny amount, treatment needs a controlled, larger dose aimed at the unwanted tissue while sparing healthy tissue.
recall that some nuclei are unstable and may split, and relate such effects to radiation which might emerge, to transfer of energy to other particles and to the possibility of chain reactions (to include: knowledge of the term nuclear fission for fission to occur the unstable nucleus must usually first absorb a neutron) (content found only in the physics separate science qualification)
Some nuclei are unstable and may split in a process called nuclear fission. For fission to occur, the unstable nucleus usually first absorbs a neutron; the nucleus then splits into two smaller nuclei and releases further neutrons together with energy. The energy is transferred to the surrounding particles and material, raising their kinetic and thermal energy. The neutrons released can be absorbed by other unstable nuclei, causing them to split in turn, so a chain reaction becomes possible. Radiation such as gamma rays may also emerge from the fission products, which are often themselves unstable. In a controlled reactor the chain reaction is regulated; in an uncontrolled situation it can grow rapidly.
describe the process of nuclear fusion (to include: knowledge that mass may be converted into the energy of radiation) (content found only in the physics separate science qualification)
Nuclear fusion happens when two light nuclei, such as the hydrogen isotopes deuterium and tritium, are forced close enough together that the strong nuclear force binds them into one heavier nucleus, for example helium. Because the total mass of the product nucleus is slightly less than the combined mass of the original nuclei, the missing mass appears as energy of radiation, often carried away by a fast neutron and gamma rays. This is the process that powers stars, where very high temperature and pressure let nuclei overcome their electrostatic repulsion. Fusion differs from fission, which splits a heavy nucleus. In a multiple-choice question, identify the option that names light nuclei joining and states that mass is converted into radiation energy.
Your focus
- Distinguish contamination from irradiation in a given scenario
- Describe how contamination can enter and remain in the body
- Compare the hazards of contamination and irradiation using persistence and spread
Show all 15 objectives
- Define half-life and apply it to a described source
- Explain how half-life affects how long a hazard persists
- Compare the hazards of a short-half-life and a long-half-life material
- Describe how nuclear radiation is used to explore internal organs
- Describe how nuclear radiation is used to control or destroy unwanted tissue
- Justify the choice of radiation type for each medical use
- Recall that unstable nuclei may split by nuclear fission after absorbing a neutron
- Relate fission to the energy transferred to other particles and to radiation that may emerge
- Explain how released neutrons make a chain reaction possible
- Describe nuclear fusion as light nuclei joining to form a heavier nucleus.
- Explain that the mass difference is converted into the energy of radiation.
- Distinguish fusion from fission in a multiple-choice context.
Uses and hazards exam tips
Marking Points
- States that contamination transfers radioactive material onto or into an object or person, so the source is carried with them
- States that irradiation is exposure to radiation from a source that remains outside the body, so the person does not become radioactive
- Explains that contamination can be taken into the body by inhalation or ingestion and continues to deliver dose until removed
- Explains that irradiation delivers dose only during exposure, so increasing distance, adding shielding or reducing time lowers the hazard
- Compares the two hazards by noting that contamination can spread to other places and people whereas irradiation does not transfer the source
- Defines half-life as the time taken for the activity of a sample to halve
- Explains that a short half-life gives a rapid fall in activity, so the hazard decreases quickly
- Explains that a long half-life gives a slow fall in activity, so the material stays hazardous for a long period
- Links half-life to persistence in the environment or the length of time precautions are needed
- Compares two materials with different half-lives to show how the hazard differs
- Identifies gamma radiation as suitable for imaging internal organs because it penetrates tissue and can be detected outside the body
- Explains that a tracer emitting radiation is taken into the body and its distribution is detected to build an image of an internal organ
- States that radiation can be directed at unwanted tissue such as a tumour to damage its cells and control or destroy it
- Distinguishes the small tracer amount used for exploration from the larger targeted dose used for treatment
- Recognises that alpha and beta radiation are largely absorbed within the body and so are less useful for imaging from outside
- States that some nuclei are unstable and may split in a process called nuclear fission
- Recalls that for fission to occur the unstable nucleus must usually first absorb a neutron
- Describes that fission releases further neutrons and energy, which is transferred to other particles and surrounding material
- Explains that released neutrons can trigger further fissions, making a chain reaction possible
- Identifies that radiation such as gamma rays may emerge from the unstable fission products
- Selects the option in which two light nuclei join to form a single heavier nucleus.
- Recognises that the total mass after fusion is slightly less than the mass before.
- States that the lost mass is converted into the energy of radiation.
- Distinguishes fusion, which joins light nuclei, from fission, which splits a heavy nucleus.
- Identifies the very high temperature and pressure needed to bring nuclei close enough to fuse.
Examiner Tips
- 💡Decide first whether the radioactive material itself moves to the person; if it does, the situation is contamination
- 💡Use the words 'source stays outside the body' when describing irradiation to keep the distinction sharp
- 💡When comparing hazards, mention both persistence of dose and spread to other people or surfaces
- 💡Define half-life precisely before applying it to hazard
- 💡Use a paired example, one short and one long half-life, to make the comparison explicit
- 💡Separate the two ideas: intensity of emission now versus how long the hazard lasts
- 💡Link each use to a property of the radiation: penetration for imaging, cell damage for treatment
- 💡Name the type of radiation you choose and justify it in one clause rather than just naming it
- 💡Keep the two uses clearly separated in your answer so each clause of the question is addressed
- 💡Use the exact term nuclear fission and state the neutron-absorption step explicitly
- 💡Show the chain reaction as a sequence: neutron absorbed, nucleus splits, more neutrons released, further nuclei split
- 💡Mention both the energy transfer to other particles and the radiation that may emerge, since the statement asks for both
- 💡Read every option and reject any that describes splitting rather than joining.
- 💡Look for the option that mentions both light nuclei joining and mass becoming radiation energy.
- 💡Link the answer to stars, where fusion occurs naturally, to check your reasoning.
Common Mistakes
- Claims that an irradiated person becomes radioactive; correct this by stating that irradiation leaves no radioactive material on the person
- Treats contamination and irradiation as the same hazard; distinguish them by whether the radioactive material itself is transferred
- Assumes a contaminated object stops being a hazard once removed from the source; note that the transferred material keeps emitting until it is removed or decays
- States that a short half-life always means a lower hazard; explain that it emits intensely while fresh even though it decays quickly
- Confuses half-life with the time for all activity to stop; state that activity halves in each half-life and never reaches zero in this model
- Ignores the separate-science scope and treats the point as core content; keep the explanation within the physics separate science qualification
- Chooses alpha radiation for imaging because it is 'strong'; correct this by noting that alpha is absorbed within a few centimetres of tissue and cannot escape to a detector
- Assumes the same dose serves both imaging and treatment; correct this by separating a tiny tracer amount for exploration from a controlled larger dose for destroying tissue
- Treats radiation treatment as harmless to all cells; correct this by stating that the dose is aimed at unwanted tissue and healthy tissue is shielded as far as possible
- Says fission happens spontaneously without any trigger; correct this by stating that the unstable nucleus usually first absorbs a neutron
- Confuses fission with fusion; correct this by describing fission as a large nucleus splitting rather than small nuclei joining
- Omits the released neutrons when explaining chain reactions; correct this by stating that each fission can release neutrons that trigger further fissions
- Chooses the option that describes a heavy nucleus splitting; correct this by recalling that fusion joins light nuclei.
- Assumes that mass simply disappears with no energy released; correct this by stating that the mass difference becomes radiation energy.
- Confuses fusion with radioactive decay; correct this by noting that fusion combines nuclei rather than emitting particles from an unstable one.
- Believes fusion needs no energy input; correct this by noting that high temperature and pressure are needed to overcome repulsion.