Chapter 17 · Radioactivity and Nuclear Chemistry
17.4Detecting Radioactivity
8 min · two checks
Predict
What does a Geiger counter actually count?
The idea
- Describe detection as ionization or exposure of film.
- Distinguish activity from a mere presence of an element.
You cannot see a nuclear emission, but you can see what it does to matter. Film darkens. A Geiger–Müller tube registers a current pulse when radiation ionizes the gas inside. Scintillators flash when struck, and the flashes are counted. Dosimeters accumulate a dose for a person wearing them. All of these measure events, not chemical amounts.
Background radiation is always there: cosmic rays, radon, potassium-40 in your body and in granite. A reading means something only compared with background and with the distance and shielding around the source. Detection is easy to misread as danger by itself. The type of radiation, the energy, the time, and whether the source is inside or outside the body all decide the dose.
Keep these
- Detectors count ionization, flashes, or film exposure.
- Background is never zero.
- A count rate is not yet a medical dose.