1 Alpha Emissions (How a Smoke Alarm Works)

2 Radioactive Emissions (Radiation) Penetrating Power SymbolEquivalentDescriptionType He Stopped by thick paper (  ) Helium nucleus Dense (+) charged particle 4 2 Stopped by 6mm of Al High speed electron (-) charged particle e 0  0 Alpha Beta Gamma Stopped by several cm of Pb High energy photons Type of energy  0 0

3 Penetrating Power of Radioactive Emissions

4 How Smoke Alarms Work An example of an every day device that uses alpha decay is a standard home smoke alarm. The smoke alarm contains a small amount of Americium-241 a radioactive isotope of Americium-243. Americium-241 undergoes alpha decay. A smoke alarm uses the emitted alpha particles and an ionization chamber to detect smoke particles in the air.

5

6 How Smoke Alarms Work Click here for a short video of how smoke alarms work.

7 The smoke alarm contains an ionization chamber containing two charged metal plates, one with a positive charge and one with a negative charge. The emitted alpha particles are directed to travel between these two plates. How Smoke Alarms Work Americium source charged metal plates

8 When air (diatomic nitrogen and diatomic oxygen) molecules pass between the charged plates, they may be struck by the alpha particles. The nitrogen and oxygen molecules lose electrons and become ionized. The lost electrons travel towards the positive plate and the ionized oxygen and nitrogen travel to the negative plate. This produces a small but steady flow of electrical current in the smoke detector circuitry. How Smoke Alarms Work oxygen molecules nitrogen molecules electron charged plates Americium source

9 When smoke enters the ionization chamber with the air, it reduces the number of ions that flow to the plates and the electrical current drops. How Smoke Alarms Work oxygen molecules nitrogen molecules smoke particle charged plates Americium source current meter battery

10 When the smoke particles cause the electrical current to drop below a lower limit, the alarm circuit is triggered and the smoke alarm sounds off. How Smoke Alarms Work