1 alpha emissions (how a smoke alarm works). 2 radioactive emissions (radiation) penetrating power...
TRANSCRIPT
1
Alpha Emissions
(How a Smoke Alarm Works)
2
Radioactive Emissions (Radiation)
Penetrating Power
SymbolEquivalent
Description
Type
He Stopped by thick paper ()
Helium nucleus
Dense (+) charged particle
42
-1
-1
Stopped by 6mm of Al
High speed electron
(-) charged particle
e0
0
Alpha
Beta
Gamma
Stopped by several cm of Pb
High energy photons
Type of energy 00
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