State the effects of ionising nuclear radiations on living things, including cell death, mutations and cancer

5.2.5 Effects of Ionising Radiation on Living Things – Safety Precautions

Key Learning Objectives

• Explain how ionising radiation damages living tissue.
• State the three biological effects required by the syllabus:

  • Cell death – loss of cell viability.
  • Genetic mutation – permanent change in the DNA sequence.
  • Cancer – uncontrolled cell growth caused by mutations in oncogenes or tumour‑suppressor genes.

• Distinguish deterministic (tissue) effects from stochastic (probabilistic) effects and use the exact syllabus wording (“no threshold for stochastic effects”).
• Apply the four core safety‑precaution principles (time, distance, shielding, ALARA) to the safe handling, transport and storage of radioactive material.

Ionising Radiation – Types (for context only)

These types are often introduced earlier in the syllabus; they are not examined in 5.2.5 but help understand shielding requirements.

Biological Effects of Ionising Radiation

1. Cell Death

• Necrosis – uncontrolled rupture of a cell caused by severe damage.
• Apoptosis – programmed cell death that is triggered when DNA damage cannot be repaired.
• High doses (often described as a “large” dose) can kill cells immediately; lower doses may allow survival with damage that can later lead to other effects.

2. Genetic Mutations

• Radiation can break chemical bonds in DNA, producing:

  • Point mutations (single‑base changes)
  • Insertions or deletions of DNA segments
  • Chromosomal rearrangements (e.g., translocations)

• If the cell’s repair mechanisms copy the error incorrectly, the change becomes permanent and can be passed to daughter cells.

3. Cancer

• Cancer arises when mutations affect genes that control cell division (oncogenes, tumour‑suppressor genes).
• This is a stochastic effect – there is no threshold; the probability of cancer increases with the dose, but a specific dose does not guarantee cancer.
• Risk is greatest in rapidly dividing tissues (bone‑marrow, gastrointestinal lining, skin).
• Enrichment (optional): Roughly a 5 % increase in the chance of fatal cancer is estimated for every 1 Sv of whole‑body exposure. (Not required for the exam.)

Deterministic vs Stochastic Effects

1. Deterministic (tissue) effects – have a threshold dose; severity increases with dose above that threshold. Examples only (not exhaustive): skin reddening, cataracts, radiation burns.
2. Stochastic (probabilistic) effects – no threshold; only the chance of the effect rises with dose. Example: induction of cancer.

Core Safety‑Precaution Principles

These four principles must be stated explicitly in the exam.

• Time – Reduce the period spent near a source.
• Distance – Increase the distance from the source (inverse‑square law).
• Shielding – Use appropriate material for the type of radiation:

  • Alpha: paper or thin plastic
  • Beta: a few millimetres of aluminium
  • Gamma / X‑ray: lead or several centimetres of concrete
  • Neutron: water, concrete or specialised hydrogenous material

• ALARA – Keep exposures “As Low As Reasonably Achievable”.

Practical Application of the Principles

Safe Handling

• Label every source with radionuclide, activity and hazard symbols.
• Keep sources in sealed, lead‑lined containers when not in use.
• Wear appropriate PPE: lead aprons, gloves, eye protection and, where relevant, thyroid shields.

Transport

• Move sources in sturdy, clearly labelled containers.
• Use shielded carts or trolleys; never carry an open source by hand.
• Plan the route to minimise time and distance from other persons.

Storage

• Store in a locked, ventilated cupboard or radiation‑shielded room, away from public areas and high‑traffic zones.
• Post “Radioactive – Keep Away” signs on doors to rooms or cupboards containing sources.
• Maintain a written register showing:

  • Source identification (type, activity, date received)
  • Current location
  • Dates of use and any incidents

Emergency Preparedness

• Know the location of spill kits, emergency showers and eye‑wash stations.
• Follow the school’s emergency procedure: isolate the area, evacuate if necessary, and report the incident to the radiation safety officer.

Dosimetry (Enrichment Only)

Students may be told that workers wear personal dosimeters and must not exceed the occupational limit (e.g., 20 mSv per year). This information is useful background but is not examined.

Summary

Ionising radiation can cause immediate cell death, permanent genetic mutations, and a long‑term increase in the risk of cancer. Deterministic effects have a dose threshold, whereas stochastic effects have no threshold and only the probability rises with dose. By applying the four core safety principles – time, distance, shielding and ALARA – and following strict handling, transport and storage rules, we protect ourselves, other users and the public from these biological hazards.