Smoke Detectors : Uses of radioisotopes

Key Concepts

• a positive electrode

• a negative electrode

• a radiation source (eg, Americium-241)

• a current detector

• Americium-241 decays to produce Neptunium-237 and an alpha particle (⁴₂He).

  241			4			237
  	Am	→		He	+		Np
  95			2			93

• Alpha particles cause the oxygen and nitrogen molecules in air to ionize:
  O₂   →   O₂⁺ + e^-

• Positively charged particles, alpha particles and O₂⁺, move to the negative electrode.
      Negatively charged particles, electrons, move to the positive electrode.

• The flow of charged particles between the electrodes causes a current to flow.

• When smoke is present, alpha particles attach to the smoke particles so air
      molecules are no longer ionized, the current drops, causing an alarm to sound.
  

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