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Homeowners gulped after reading newspaper stories that conjured up frightening images of a Three-Mile Kitchen Island. The reports were about granite countertops that contain radium, which can emit radon, a radioactive gas that can cause lung cancer.
The U. Environmental Protection Agency has published guidelines regarding permissible concentrations of radon in air. The Health Physics Society, after testing several samples of commercial granite, concluded that the radon produced by a typical granite countertop would be about 30 times lower than the level laid out in the EPA guidelines. Granites can be black, gray, pink or red, depending on the colors of the constituent minerals.
A study published in the Journal of Radioanalytical and Nuclear Chemistry in found that the radium content of red and pink granites is about three-and-a-half times higher than that of black and gray granites.
Radium is the immediate precursor to radon in the uranium decay series; therefore, radon emission is directly proportional to radium content. It is likely that radiation damage caused by uranium imparts a pinkish or reddish color to certain minerals in the granite. The term texture refers to the size and shape of crystals in a rock.
A texture comprising very large crystals or veins could be an indicator of high uranium content. When a rock is polished, the veins may appear as striations. In this method, a standard room is considered 4. Radon is a major contributor to the ionizing radiation dose received by the general population [ 1 ]. Concentrations of U and Ra in some terrestrial materials such as alum shale and black shale are high.
Construction materials that used as building materials are sources of indoor airborne radioactivity and external radiation from the decay series of uranium in buildings [ 2 ].
It is important to estimate the impress and contribution of the different building materials that can deed as Rn sources or Rn absorber inside of buildings for residence and work. According some reports, the granite stones have a higher radon exhalation rate than other terrestrial materials on average [ 3 — 6 ].
The most abundant of plutonic rock in mountain belts and continental shield areas were made by granite stones. Types of batholith stones that may in dwell thousands of km 2 are usually intimately associated with granodiorite, quartz, gabbro and diorite.
They are scratch resistant and extremely durable; their hardness lends themselves for the stone to be mechanically polished to a high gloss finish. They mainly contain of large grains of potassium, sodium feldspars and quartz. Applying this definition requires the mineral identification and quantification abilities of a competent geologist. Other components of granites stones are hornblende and mica.
In general, it was widely believed that granite stones were formed mostly from magmatic differentiation of basaltic magma. The evidence of this exegesis was considered to indicate a metamorphic origin [ 7 ]. Figure 1 illustrates the generalized mineral composition of igneous rocks. Granites and rhyolites compositionally equivalent to granite but of a fine grain size are composed mainly of orthoclase feldspar, quartz, plagioclase feldspar, mica and amphibole.
Granite composition diagram. All glasses made by using silica even wine glasses, eye glasses, windows, mirrors, etc. Figure 2 shows the percentage of radon source in residential place. As seen in figure, only 2. It is quarried and processed to produce commercial products such as countertops. What advice does the EPA have about radon for consumers who have granite countertops? EPA believes the principal source of radon in homes is from the soil in contact with basement floors and walls.
To reduce the radon risk you should first test the air in your home to determine the radon level. There are many do-it-yourself radon test kits available through retail outlets and on-line, starting at about While natural rocks such as granite may emit radiation and radon gas, the levels attributable to such sources are not typically high.
Contact your state radon office www. Hire a qualified radon professional www. The key to reducing your risk of lung cancer from radon is to test your home and mitigate when necessary. A specially-trained and qualified radiation professional may be equipped to test for other radon sources such as granite or diffusion from drinking water when diagnosing the nature and source of your home's radon problem. Learn more about radon, visit www.
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