AP Chemistry II Smoke Detector Experiment

Inexpensive ionization-type smoke detectors contain americium-241, which undergoes alpha-decay with a half-life of 432.2 years. As the ²⁴¹Am decays, the positive alpha particles ionize the nitrogen and oxygen molecules in the air. These ions produce a small electric current, which is detected in an ionization chamber in the smoke detector.

When smoke is present, the smoke particles in the air neutralize the ions, which lowers the current at the detector. When the smoke detector senses a reduction in current, it sounds the alarm.

The objective of this lab is to measure the number of counts per minute produced by the ²⁴¹Am, and use this measurement to estimate the quantity of ²⁴¹Am in the dector.