Radioactivity inside our home
American essayist Ralph Waldo Emerson wrote, “As soon as there is life, there is danger.†Every day of our lives we face many dangers, some obvious, some hidden. One such hidden danger pervasive in every nook and cranny of our home is the carcinogenic radiation from radon. We live on a planet that is literally bathed in radiation - from high energy gamma rays to low energy radio waves. Some of it comes from outer space in the form of cosmic rays, others from diagnostic X-rays, mammograms, CAT scans, radiation therapies, rocks, soil, smoke detectors, etc. These are known as background radiation. Apart from background radiation (~160 millirem/year), largest dose of radiation we receive (~200 millirem/year) comes from exposure to the ubiquitous radon gas. To put this in perspective, the average dose from a chest X-ray is 10 millirem. Radon is a radioactive nucleus. The process by which an unstable nucleus spontaneously decays by emitting one or more particles with an accompanying radiation is called radioactivity. The time taken for half of the nuclei in a sample to decay into a more stable nucleus is called the half-life. It takes ten half-lives to reduce the intensity of radiation to approximately one-thousandth (1/2 raised to the power 10) of the original intensity, at which point the nucleus is considered safe. Radon is everywhere - in the rocks, soil, water, and air. It is continuously produced in a chain of radioactive decay of uranium-238, thorium-232, and radium-226 atoms that are found abundantly in the Earth's crust. Radon has several radioactive isotopes. An isotope is the same nucleus with different number of neutrons. For example, radon-220 with 86 protons and 134 neutrons is an isotope of radon-222 with 136 neutrons. Of greater concern to us is radon-222 with a half-life of 3.8 days. It has sufficient time (380 days) to diffuse through permeable soil and enter homes through cracks and crevices in the foundation and other openings. Radon dissolves easily in water. Hence, traces can be found in drinking water as well. The radioactive decay chain of radon-222 is rather long. It starts with polonium-218 followed by isotopes of lead, bismuth, polonium, and ends with stable lead-206. At every step of the decay process, alpha (helium nucleus) or beta (electron) particles are emitted. One of the decay products, polonium-210, is so lethal it was used by KGB in 2006 to kill Alexander Litvinenko, a Russian political émigré in the U.K. Radon is colorless, tasteless, odorless, and chemically inert. Because of its inertness the radon we breathe is not dangerous. However, it is the decay products that are dangerous. The various nuclei produced in the decay process of the inhaled radon lodge in the lining of the lungs and cause somatic effects, such as damage of the cells. The alpha particles and lead, in particular, strike sensitive lung tissue causing damage that can lead to lung cancer. For smokers, the effect is synergistic and will cause death in the extreme. Other effects may include cataracts, leukemia, gastrointestinal problems, and stomach cancer. It is estimated that life expectancy of a person exposed to at least 300 millirem of radiation a year decreases by about 15 days per exposure. Radon is an ionizing radiation capable of ejecting one or more bound electrons from an atom or molecule. If the positively ionized atom or molecule is part of a biological system, severe consequences can result, such as changing of normal cells into cells that can in the end become cancerous. Cell mutations are of greatest long-term worry, because they may affect future generations by way of disrupting normal development of the fetus. What is considered a safe level of radon gas? There is no safe level. Zero is perhaps the safest level. The concentration of radon reaches an uncomfortably high level in well-insulated homes during winter months. Furthermore, intensity of radiation from radon progeny is highest during the first few hours of radioactivity, when bismuth and polonium quickly decay into radioactive lead-210. What can we do to mitigate the health related effects of radon? Honestly, not much except sealing cracks in the walls, floors or the concrete slab. A well-ventilated house will have lower level of radon concentration, but never zero level. Just like the risk of an accident while driving a car, radiation from radon is another daily risk that we have to face. We have no choice but to breathe the air in our home; we have to live with radiation. So, why be fearful? When predictable, avoid radioactivity; when inevitable, accept and tame it.
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