Explain safety precautions for all ionising radiation in terms of reducing exposure time, increasing distance between source and living tissue and using shielding to absorb radiation
IGCSE Physics 0625 – Safety Precautions for Ionising Radiation
5.2.5 Safety Precautions for Ionising Radiation
Ionising radiation (alpha, beta, gamma, X‑rays and neutrons) can damage living tissue.
The three fundamental ways to reduce the dose received are:
Reduce the time of exposure.
Increase the distance between the source and the tissue.
Use appropriate shielding to absorb or attenuate the radiation.
1. Reducing Exposure Time
The dose \$D\$ received is the product of the dose‑rate \$\dot{D}\$ and the exposure time \$t\$:
\$D = \dot{D}\,t\$
Therefore, halving the time of exposure halves the dose. Practical measures include:
Plan experiments so that the source is only uncovered for the minimum necessary period.
Use remote handling tools (tongs, manipulators) to keep the operator away from the source.
Record the exact time a source is open and close it promptly.
2. Increasing Distance (Inverse Square Law)
For point sources, the intensity \$I\$ of radiation follows the inverse square law:
\$I \propto \frac{1}{r^{2}}\$
Doubling the distance \$r\$ reduces the intensity to one‑quarter. Practical steps:
Work from the greatest feasible distance; use view‑ports or cameras when possible.
Place shielding material between the source and the user rather than behind the user.
Mark safe zones around high‑activity sources.
3. Shielding
Shielding works by absorbing or scattering radiation. The effectiveness depends on the type of radiation and the material’s atomic number (Z) and density.
Radiation Type
Effective Shielding Material
Typical Thickness for 90 % Attenuation
Alpha (\$\alpha\$)
Paper, thin plastic, skin
\overline{0}.01 mm (a sheet of paper)
Beta (\$\beta\$)
Plastic (acrylic), aluminium
\overline{1} mm plastic or 2 mm aluminium
Gamma / X‑ray (\$\gamma\$, \$X\$)
Lead, concrete, steel
\overline{5} mm lead or 10 cm concrete
Neutron
Water, polyethylene, borated rubber
\overline{5} cm polyethylene (with boron additive)
Key points when selecting shielding:
Use low‑Z material (plastic) for beta particles to avoid bremsstrahlung X‑rays.
High‑Z material (lead) is best for gamma rays but must be thick enough.
Combine materials (e.g., plastic + lead) for mixed radiation fields.
Practical Laboratory Checklist
Verify that all sources are stored in lead‑lined containers when not in use.
Wear personal protective equipment (lab coat, gloves, eye protection).
Use a radiation survey meter to confirm that area dose rates are within safe limits before starting work.
Post clear signage indicating radiation hazards and required safety distances.
Ensure emergency procedures (spill kits, first‑aid, evacuation routes) are known to all personnel.
Suggested diagram: A cross‑section showing a radiation source, the three safety measures (time, distance, shielding) and a worker using a remote manipulator.