1. Smoke Detectors Brief history
Jr. Lab II, sp’01
Brief history
1930s, Swiss scientist Walter Jaeger tried to invent poison gas detector thinking the particles would interact with an ion gas causing a detectable change in current. The idea failed. Frustrated, he lit a cigarette and voila, smoke detector. [1]

2. Two Types Photoelectric Ionization
Smoke particles encounter light beam
Beam scatters to a photocell creating a current
Better for larger particles (smoldering)
Ionization
Particles attach to ionized particles creating a detectable change in current
Better for smaller particles (flaming)

3. Ionization Smoke Meters

4. Ionization Source Americium-241,243?
Emits  particle which ionizes the air molecules
Isotope
Mass
Half-life (years)
Mode of decay
241Am
432.2
 to 237Np
243Am
7370
 to 239Np
[2]

5. References
[1] Bunker, Merton Jr., Scientific American, “Smoke Detectors,” Apr
[2]
chemistry.about.com/science/chemistry/library/weekly/aa020700a.htm
Geoffrey,