Smoke detectors use a small amount of americium-241 (an alpha emitter). The alpha particles ionise the air between two electrodes, creating a tiny current. When smoke enters the detector, it absorbs the alpha particles and reduces the current — this triggers the alarm. Alpha is used because it is strongly ionising (good for creating the current) and is blocked by even a small amount of smoke or air. Crucially, alpha cannot escape the detector casing, making the device safe to have in homes.
Paper thickness control uses beta radiation. A beta source on one side and a detector on the other measure how much beta passes through the paper. If the paper is too thick, less beta gets through; if too thin, more gets through. The detector feeds back to rollers that adjust the paper thickness automatically.
Checking welds uses gamma radiation — it penetrates the metal and reveals cracks or flaws on a detector or photographic film placed on the other side. Alpha and beta cannot penetrate thick metal, so only gamma is suitable here.
This deep dive covers Industrial Uses of Radiation within Uses & Hazards of Radiation for GCSE Physics. Revise Uses & Hazards of Radiation in Atomic Structure for GCSE Physics with 18 exam-style questions and 5 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 4 of 17 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Uses & Hazards of Radiation
Which type of radiation is used in smoke detectors?
Explain how a smoke detector uses an alpha source to detect smoke.