Some products you own and use regularly might contain radioactivity or emit radiation. They are an example of the many ways radiation use benefits our modern society. When they are used according to their instructions for use, you are not exposed to radiation.
Products in your home that contain radioactivity, but are not hazardous to anyone’s health, include smoke detectors, some foods, and fertilizers.
Smoke detectors sometimes contain a small amount of a radioactive source (americium-241) within a metal chamber. In a smoke detector, the radioactivity in the source emits a constant stream of alpha particles that are sensed by a small radiation detector, causing a small current. If smoke comes between the source and the detector, the current is decreased, leaving nothing for the detector to sense, and the alarm goes off.
Some foods become radioactive by absorbing naturally occurring radionuclides from surrounding soils as they grow or some of the ingredients used to make them may be naturally radioactive. Fertilizers that you use for your gardens, lawns, etc., might contain radioactive potassium or uranium in small amounts.
Other items that contain radiation but are no longer manufactured—and are of interest to collectors and those who acquire antiques—are watches and clocks; glassware (canary or Vaseline glass), tile, and ceramics; gas lantern mantles; and camera lenses. Some old watches and clocks have dials that were painted with a radiation-emitting compound to make them visible in the dark. Old glassware, tile, and ceramics that contain radioactivity generally have enhanced naturally occurring radionuclides (such as uranium, thorium, or potassium) incorporated right into the glass or into the glaze. An older-style gas lantern mantle with thorium in its silk threads is often used by radiation safety offices as a source to check the operation of their radiation-detection instruments. Old camera lenses also might contain some thorium, which was believed to create a better image on the film.
It is important not to assume that all types of a certain item contain radioactivity or emit radiation; for example, some smoke detectors and old watches contain radioactivity, but not all do. And these radioactivity-containing items don’t pose a radiation hazard to you unless you were to eat them—and eat a lot of them!