Why There's Nuclear Material on Your Ceiling: The Physics Inside Smoke Detectors
Most people don’t realize that a small radioactive source sits quietly in their hallway, emitting alpha particles 37,000 times per second. It’s been there for years, possibly decades, and it’s one of the most successful life-saving devices ever invented. The humble smoke detector contains about 0.3 micrograms of americium-241—a byproduct of nuclear reactors—and understanding how it works reveals a fascinating intersection of nuclear physics, electrical engineering, and fire science. The Accidental Discovery In the late 1930s, Swiss physicist Walter Jaeger was attempting to build a sensor for poison gas. His approach used an ionization chamber: air molecules between two charged plates would be ionized by a radiation source, creating a small electrical current. When poison gas entered, he expected it to bind to the ions and change the current. ...