Classify alpha, beta and gamma properties without treating penetration as the only risk.
Method and worked examples
Ionising radiation can remove electrons from atoms and damage living tissue. Alpha particles are strongly ionising over a short range and have low external penetration. Beta particles usually penetrate farther but less than gamma rays. Gamma photons are less densely ionising along a path and more penetrating; shielding attenuates them rather than providing a universally perfect stop. Actual ranges depend on energy and material.
External exposure can be reduced by minimising time, increasing distance and choosing suitable shielding. Contamination means radioactive material is present on or inside an object or person; irradiation means exposure to radiation. A weakly penetrating alpha emitter can be hazardous inside the body. Use the stated geometry and radiation type when applying these rules; a closed-answer classification does not authorise handling sources.
Example 1
Which is usually most penetrating: alpha, beta or gamma radiation of common educational examples?
Gamma is generally most penetrating. This ordering describes typical examples, not identical energies or a universal ranking of biological risk.
Example 2
A source is used for 10s instead of 40s at unchanged dose rate. What is the exposure fraction?
Dose is proportional to time at constant rate. The fraction is 4010=41, or 25%.
Watch out:Low external penetration does not imply low internal risk. Inhaled or ingested emitters can irradiate nearby tissue intensely.
29. Ionisation, penetration and protection rules | Year 11 Physics | Ascent Arcade