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Radioactivity is a topic that tends to get hyped-up coverage in the media. It is something that we cannot see, smell or hear. The same can be said for most forms of electricity and electromagnetic radiation. Tools such as volt/amp meters and oscilloscopes give us a view into the invisible world of electricity. A geiger counter allows radioactivity to be observed and measured in a similar fashion. There is a lot of folklore, information, and mis-information online concerning radioactivity. Some real-world experience can help to demystify the properties of natural and man-made radioactive materials.
A practical use for a geiger counter is to locate low level radioactive sources in and around the household, it can be a good idea to move stronger sources away from your living space. Examples of radioactive materials that can be found inside the house include rock and mineral colections, certain pottery glazes, gas lantern mantles, glow-in-the-dark watch and radio dials and certain welding rods. Radon gas can often be found in basements, depending on the local geography. Lime-green depression glass, yellow and orange Fiesta Ware plates and decorative tiles can contain uranium. Some larger transmitting-type vacuum tubes can contain uranium in the glass seals an thorium in the filaments, both are radioactive elements.
Common household smoke detectors manufactured between the early 1960s and the early 2000s typically contained a tiny piece of radioactive americium 241, which mainly emits alpha particles. Very little alpha radiation eminates from this ionization type of detector because it is blocked by a metal shield and the smoke detector's plastic case. The life-saving capabilities of these smoke detectors far outweighed any negative effects of their small amount of radioactive material. That said, newer smoke detector technologies have shifted to the use of optical detection methods due to its higher sensitivity. Certain types of industrial smoke detectors contain radium, which is much more radioactive than americium. These detectors are usually metallic cylinders with a screened section and are mounted hanging down from a ceiling. For more information, see the Wikipedia article on smoke detectors.
Keep in mind there is, and has always been, a fair amount of normal background radiation from naturally ocurring radioactive minerals in the ground and the radon gas produced by the decay of the same minerals. Above-ground atomic testing in past years has increased the background radiation levels somewhat, but this is mostly a concern for people living close to nuclear test sites.
Here are some projects that can improve and extend the capabilities of readily available surplus geiger counters such as the Victoreen CDV-700.
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