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CIE iGCSE Co-ordinated Sciences-P5.2.5 Applications and safety precautions- Study Notes- New Syllabus

CIE iGCSE Co-ordinated Sciences-P5.2.5 Applications and safety precautions – Study Notes

CIE iGCSE Co-ordinated Sciences-P5.2.5 Applications and safety precautions – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.

Key Concepts:

Core

1. Know the following applications of radioactivity:
(a) household fire (smoke) alarms
(b) irradiating food to kill bacteria
(c) sterilisation of equipment using gamma rays
(d) measuring and controlling thicknesses of materials with the choice of radiations used linked to penetration and absorption
(e) diagnosis and treatment of cancer using gamma rays
2. State the effects of ionising nuclear radiation on living things, including cell death, mutations and cancer
3. Describe how radioactive materials are moved, used and stored in a safe way in terms of time, distance and shielding

CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics

Applications of Radioactivity

(a) Household Fire (Smoke) Alarms:

  • Contain a small source of α-particles (e.g., Americium-241).
  • α-particles ionise the air, allowing a tiny electric current to flow between electrodes.
  • When smoke enters, it absorbs α-particles → ionisation decreases → current drops → alarm sounds.
  • α-particles are chosen because they are highly ionising but weakly penetrating (safe to use inside the device).
  • The amount of radioactive material used is extremely small and does not pose a health risk.

(b) Irradiating Food to Kill Bacteria:

  • γ-rays from Cobalt-60 are commonly used.
  • Kills bacteria, mould, and insects, helping preserve food longer.
  • Prevents food-borne diseases without making the food radioactive.
  • Maintains nutritional value and appearance of food (safe method).
  • Used especially for spices, dried fruits, and packaged foods for export.

(c) Sterilisation of Equipment:

  • γ-rays used to sterilise surgical tools, bandages, and medical disposables.
  • Destroys bacteria, viruses, and fungi without heating the material.
  • Allows sterilisation after packaging, ensuring equipment stays sterile until opened.
  • Safer than chemical sterilisation (no toxic residues).
  • Essential in hospitals and pharmaceutical industries.

(d) Measuring and Controlling Thickness of Materials:

  • Used in industries making paper, plastics, or metal foils.
  • A radioactive source is placed on one side of the material and a detector on the other side.
  • As thickness changes, the amount of radiation reaching the detector also changes.
  • Automatic machines adjust the rollers to maintain correct thickness.
  • Choice of radiation: β for thin materials, γ for thick metals, α unsuitable (blocked by paper/air).

(e) Diagnosis and Treatment of Cancer:

  • γ-rays used in radiotherapy to kill cancer cells deep inside the body.
  • Beams are rotated around the patient to focus on tumour and reduce damage to healthy tissues.
  • Radioactive tracers (β or γ emitters) are used in medical imaging (e.g., PET scans) to diagnose diseases.
  • Tracer isotopes are chosen for their short half-life → minimise patient exposure.
  • Radiotherapy is often combined with chemotherapy or surgery for better results.

Example

Why are γ-rays used in radiotherapy instead of α or β particles?

▶️Answer/Explanation

Step (1): α-particles are too ionising and cannot penetrate deep enough into the body.

Step (2): β-particles can penetrate further than α, but still do not reach deep-seated tumours effectively.

Step (3): γ-rays have a very high penetration, allowing them to reach tumours deep inside the body.

Step (4): Their intensity and direction can be controlled, reducing harm to healthy tissues.

Final Answer: γ-rays are chosen for radiotherapy because they penetrate deeply and can be targeted precisely, while α and β cannot.

Effects of Ionising Nuclear Radiation on Living Things

Cell Death:

  • High doses of radiation can kill cells instantly.
  • Can lead to tissue damage or organ failure if exposure is widespread.
  • Radiation burns on skin are caused by rapid cell death in exposed areas.
  • Excessive exposure can be fatal (radiation poisoning).

Mutations:

  • Radiation can damage DNA inside living cells.
  • Incorrect repair of DNA may lead to permanent genetic changes.
  • Mutations can be passed to offspring if reproductive cells are affected.
  • Can cause genetic disorders in future generations.

Cancer:

  • Damaged DNA in body cells may lead to uncontrolled cell division.
  • This can result in tumours and cancers developing over time.
  • Leukaemia (blood cancer) is strongly linked with prolonged radiation exposure.
  • The risk increases with both dose and duration of exposure.

Other Health Effects:

  • Can weaken the immune system by destroying white blood cells.
  • May cause radiation sickness (nausea, hair loss, fatigue).
  • High levels of exposure can damage the eyes (cataracts).
  • Long-term low exposure increases the probability of chronic diseases.

Example

A scientist is accidentally exposed to a large dose of γ-radiation. Explain the possible short-term and long-term biological effects.

▶️Answer/Explanation

Step (1): Short-term effects:
High doses can kill many cells → radiation sickness (nausea, skin burns, hair loss).

Step (2): Long-term effects:
Surviving cells may suffer DNA damage → mutations that can develop into cancers (e.g., leukaemia) years later.

Step (3): In severe cases:
Organ failure due to widespread cell death, and possibly death of the individual.

Safe Handling of Radioactive Materials

Minimising Time:

  • Limit the amount of time spent near radioactive sources.
  • Work quickly and efficiently when handling sources.
  • Use remote handling tools to speed up tasks.
  • Regular rotation of workers reduces individual exposure.

Maximising Distance:

  • The further a person is from the source, the lower the radiation dose (inverse square law).
  • Use tongs, robotic arms, or remote controls to increase distance from the source.
  • Keep sources in restricted, well-controlled areas away from the public.
  • Transport in shielded containers to avoid unnecessary exposure.

Shielding:

  • Use protective barriers to absorb radiation before it reaches workers.
  • Common shields:
    • Paper / clothing – blocks α-particles.
    • Aluminium – blocks β-particles.
    • Lead or thick concrete – blocks γ-rays and neutrons.
  • Workers may wear protective clothing (lead aprons, gloves).
  • Shielded storage rooms and lead-lined containers used for long-term storage.

Safe Storage and Movement:

  • Radioactive sources kept in lead-lined, locked containers when not in use.
  • Clearly labelled with hazard symbols.
  • Transported in approved shielded packages with proper documentation.
  • Handled only by trained and authorised personnel.

Example

A hospital technician must handle a γ-ray source for cancer treatment. Explain how the principles of time, distance, and shielding are applied to keep exposure safe.

▶️Answer/Explanation

Step (1): Time – The technician works quickly and efficiently, reducing time near the source.

Step (2): Distance – The source is moved into place using a remote-controlled arm, increasing distance.

Step (3): Shielding – The source is stored in a thick lead container when not in use, and the treatment room has lead-lined walls.

Final Answer: Exposure is minimised by limiting time, maximising distance, and using strong shielding.

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