Radon is a radioactive gas that is colorless, odorless, and tasteless, and is formed by the natural radioactive decay of uranium in soil, rock, and water. More particularly, Uranium 234 decays into Radium, which then decays into Radon gas, which then decays into daughter particles of Polonium 218, Lead 214, Bismuth 214, Polonium 214, and Lead 210. Upon decay of Radon gas, an alpha particle is produced that has an energy level of about 4.5 MeV to 5.5 MeV (million electron volts). Alpha particles can travel in air up to approximately 3.8 centimeters and can be easily stopped by as little as a piece of paper. When alpha particles contact a surface, they transfer their energy into the surface.
Radon gas is prevalent in buildings having basements or other portions of buildings on and below the surface of the ground. Studies have shown that exposure to radon gas at sufficient concentrations can cause heath problems, including among other things, lung cancer. Radon daughter particles can plate onto dust or smoke, which, when inhaled into the lungs, can stick to a surface of the lungs. When radon and its daughter particles are in intimate contact with the lung cells, the alpha, beta, and gamma particles emitted by radon and the daughter particles can cause mutation of the lung cells and initiate cancer. Accordingly, having the capability to monitor and determine radon gas levels in buildings is important for the health of its occupants.
The Environmental Protection Agency (“EPA”) has established an action level threshold of radon gas which is 4 picocuries (pCi) per hour per liter of air. Countries other than the United States may have hazard thresholds different than the threshold established by the EPA. A picocurie is a unit of radiation that indicates the number of radioactive decays. A picocurie is one million millionth, or a trillionth, of a curie, and represents about 2.2 radioactive particle disintegrations (decays) per minute per liter of air. Therefore, 4 picocuries would be 8.8 disintegrations (decays) per minute per liter of air.
Radon gas monitoring has become an integral component of real estate transactions in some states. Prior to closure of a real estate transaction in certain states, an inspector conducts a radon gas test on the premises to determine radon gas levels. This radon gas test can be conducted in a few manners. A first manner for testing radon gas levels includes using kits purchasable by consumers. Such kits include a short-term radon gas charcoal test kit and a long-term radon alpha track test kit. The short-term radon gas charcoal test kit uses a container that contains a quantity of granular activated charcoal, which absorbs the radon gas entering the canister from the surrounding air. At the end of the radon gas test period, the canister is sealed and sent to a laboratory for analysis. The long-term radon alpha track test kit includes a vessel with an internal piece of film that records the impacts of alpha particles produced by the decay of radon and its decay by-product, polonium. At the end of the radon gas test period (approximately 90 days), the radon testing kit is sent to a laboratory where the alpha tracks on the film are counted, radon concentration is computed, and analysis is reported. Such kits are relatively inexpensive, but are often times extremely inaccurate and inconsistent.
A second manner of detecting radon gas levels includes an AC powered electronic device such as that disclosed in U.S. Pat. No. 4,871,914. These types of radon monitors are relatively expensive and are generally only economical to purchase by professional radon gas inspectors who continually utilize the monitors to generate a steady flow of revenue. Such radon gas monitors are generally not economical for purchase by a typical home owner. AC power is necessary for such radon detectors because they include a powered sampling unit, in which samples are taken, that requires constant and significant quantities of power. Such a powered sampling unit is energized and draws, attracts, or otherwise influences radon gas or alpha particles into the sampling unit for sampling. Typical powered sampling units require greater than 250 volts of electrical power, which can present a shock hazard if the testing unit housing is broken. Because monitors with powered sampling units require AC power provided by a household outlet, it is often difficult to position such monitors in crawl-spaces or similar spaces that are rarely wired for AC power.
Accordingly, a need exists for an accurate, inexpensive radon gas monitor that can be powered for extended periods of time without a direct connection to an AC power source.