Some uses of radioactivity: in the home
Smoke detectors
One type of smoke detector uses Americium-241, an alpha particle source, to detect smoke.
The alpha particles pass between the two charged metal plates, causing air particles to ionise (split into positive and negative ions).
The Electrically charged particle, formed when an atom or molecule gains or loses an electron/electrons. are attracted to the oppositely charged metal plates causing a current to flow.
When smoke enters between the plates, some of the alpha particles are absorbed causing less ionisation to take place.
This means a smaller than normal current flows so the alarm sounds.
An alpha source is used because alpha radiation does not penetrate very far.
It is absorbed by a few cm of air.
This means that as long as the detector is high up on a wall, or the ceiling, it is safe for humans to be in the same room.
The source should have a long The half-life of a radioactive source is the time taken for its activity to fall to half of the original activity. Half-life is measured in seconds. so that the smoke detector does not have to be replaced too frequently, and so that the count rate remains almost constant each day.