In this paper I will discuss the element called Radon. I will explain how and when this element was discovered, its’ physical characteristics, the natural environment of the element and the abundance in which it occurs. In addition, I will describe why Radon is important to humans, and other interesting facts related to this element.
Radon has the symbol Rn. Its atomic number is 86 and its atomic weight is 222. The shell configuration is 2,8,18,32,18,8. Radon’s most stable isotope is Rn 222 with a half-life of 3.82 days. An isotope is one of two or more atoms that have the same atomic number, but have different atomic weights and mass numbers (The America Heritage Dictionary of the English Language, Third Edition, 1992). The nuclei of isotopes of the same element have the same number of protons but they have different numbers of neutrons (The America Heritage Dictionary of the English Language, Third Edition, 1992). The isotopes of a given element have identical chemical properties but varying physical properties (The America Heritage Dictionary of the English Language, Third Edition, 1992).
A radioisotope is a radioactive isotope (The America Heritage Dictionary of the English Language, Third Edition, 1992). A radioisotope is a naturally or artificially created isotope having an unstable nucleus that decays, letting off alpha, beta, gamma rays until stability is reached (The America Heritage Dictionary of the English Language, Third Edition, 1992). Radon’s melting point is -71C. The boiling point is -61.8C. Radon is the densest gas known (Concise Columbia Encyclopedia, 1995).
Radon is a heavy, colorless, odorless, tasteless, non-flammable gas (therefore it cannot be detected with the human senses) produced by the radioactive decay of radium, which is itself a product of uranium. Radioactive means the emission or transmission of energy in the form of waves through space or through a material medium; the term also applies to the radiated energy itself. The term includes electromagnetic, acoustic, and particle radiation, and all forms of ionizing radiation. According to quantum mechanics, electromagnetic radiation may be viewed as made up of photons. Acoustic radiation is propagated as sound waves. Examples of particle radiation are alpha and beta rays in radioactive, and cosmic rays. (American Heritage Dictionary of the American Language, Third edition, 1992)
It is chemically inert and does not combine with other chemicals or elements. Traces of radon are normally found in the atmosphere near the ground as the result of seepage from rocks and soil. On a worldwide average, approximately 6 atoms of radon emerge from every square inch of soil each second (Dunford, 1991). Radon is also moderately soluble in water and, therefore, can be absorbed by water flowing through rock or sand. Its solubility depends on the water temperature; the colder the water, the greater radon’s solubility.
Ernest Rutherford discovered radon in 1899. Rutherford is considered the father of nuclear physics. Indeed, it could be said that Rutherford invented the very language to describe the theoretical concepts of the atom and the phenomenon of radioactivity. Particles named and characterized by him include the alpha particle, beta particle and proton. Even the neutron, discovered by James Chadwick, owes its name to Rutherford. The exponential equation used to calculate the decay of radioactive substances was first employed for that purpose by Rutherford and he was the first to elucidate the related concepts of the half-life and decay constant. With Frederick Soddy at McGill University, Rutherford showed that elements such as uranium and thorium became different elements (i.e. transmuted) through the process of radioactive decay. At the time, such an incredible idea was not to be mentioned in polite company: it belonged to the realm of alchemy, not science. For this work, Rutherford won the 1908 Nobel Prize in chemistry.
In 1909, now at the University of Manchester, Rutherford was bombarding a thin gold foil with alpha particles when he noticed that although almost all of them went through the gold, one in eight thousand would “bounce” (i.e. scatter) back. The amazed Rutherford commented that it was “as if you fired a 15-inch naval shell at a piece of tissue paper and the shell came right back and hit you.” From this simple observation, Rutherford concluded that the atom’s mass must be concentrated in a small positively charged nucleus while the electrons inhabit the farthest reaches of the atom. Although this planetary model of the atom has been greatly refined over the years, it remains as valid today as when it was originally formulated by Rutherford.
In 1919, Rutherford returned to Cambridge to become director of the Cavendish Laboratory where he had previously done his graduate work under J.J. Thomson. It was here that he made his final major achievement, the artificial alteration of nuclear and atomic structure. By bombarding nitrogen with alpha particles, Rutherford demonstrated the production of a different element, oxygen. “Playing with marbles” is what he called it; the newspapers reported that Rutherford had “split the atom.” After his death in 1937, Rutherford’s remains were buried in Westminster Abbey near those of Sir Isaac Newton. (Concise Columbia Encyclopedia, 1995)
The two natural sources of radon, thorium and uranium, are common, naturally occurring elements that are found in low concentrations in rock and soil. Through radioactive decay, both are constant sources of radon. Radon is produced from the radioactive decay of the element radium, which is itself a decay product of either uranium or thorium. Radioactive decay is a process in which an unstable atomic nucleus undergoes spontaneous transformation, by emission of particles or electromagnetic radiation, to form a new nucleus (decay product), which may or may not be radioactive (James Long-EPA, 1998). The level of radioactivity is measured in curies, where 1 curie equals 37 billion disintegrations per second. The time required for a given specific activity of an isotope to be reduced by a factor of two is called its half-life. A picocurie (pCi) is equal to one-trillionth of a curie. Specific activity concentrations are typically measured in picocuries per gram (in a solid) or picocuries per liter (in a gas, such as air).
Radon and radiation are often referred to in very negative terms. However, the element Radon is important to humans and the general welfare of all. When radon is used under controlled conditions it has benefits for human and animal health and the overall population. Radon is used in the medical community through x-rays for diagnosing serious illnesses and determining less serious conditions such as broken bones. Radon is used chiefly in the treatment of cancer by radiotherapy. It is also valuable to scientists in the fields of biology, chemistry and physics. Radon is also used for earthquake prediction.
Radon is severe enough to have been declared a national health hazard by the Environmental Protection Agency (EPA) (Dunford, 1991). The EPA estimates up to 20,000 cases of lung cancer occur each year due to household exposure to radioactive radon gas (Dunford, 1991). While the problem was first highlighted in 1984 along the Reading Prong, a geological formation sketching through Pennsylvania, New Jersey, and New York, a survey since conducted by EPA shows high household levels of radon across the country. Environmental authorities are continuing to pinpoint areas where radon present a danger (Kelly, 1983).
Radon gas itself is not particularly harmful, but rather the subatomic particles it rapidly decays into, namely: isotopes of polonium (the most hazardous), bismuth, and lead. These radon progeny, or “daughters,” as they are often called are not only radioactive, but chemically active, as well as electostatically charged (Dunford, 1991). Because of this charge, they easily attach themselves to dust, particles in cigarette smoke, and other objects. (Dunford, 1991)
The trouble occurs when these dust and smoke particles, or the unattached elements themselves, are breathed to a great enough and long enough extent. The gas itself is usually expelled, but the progeny, perhaps as much as one third of what enters in the way of attached particles and what is believed to be close to 100% of unattached matter, lodge in the bronchial tree and lungs where they decays to a farther extent. (Dunford, 1991)
The high-energy substances generated by this process are alpha and beta particles, and gamma rays (Dunford, 1991). An alpha particle is a positively charged particle, indistinguishable from a helium atom nucleus and consisting of two protons and two neutrons. A beta particle is a high-speed electron or positron, especially one emitted in radioactive decay. A gamma rays is electromagnetic radiation emitted by radioactive decay and having energies in a range from ten thousand (104) to ten million (107) electron volts. All three are potentially harmful to human tissue, but the beta particles and gamma rays, because the have a higher power of penetration, distribute their radiation over a wider area, and therefore deliver less damage per unit of energy. Alpha particles, however, move more slowly and are denser, concentrating their radioactive energy on a smaller area (Dunford, 1991). This disrupts the cells, causing tissue damage which, if allowed to continue, could ultimately result in cancer (Dunford, 1991).
These health effects are well established from studies involving uranium miners. Actually, as long ago as the 16th century, miners in Central Europe were suffering form what they called “mountain sickness”, only later to be recognized as lung cancer. It was not until the 20th century, however, that such mines were discovered to have high concentrations of radon. This prompted the tests in the 50’s and 60’s that ultimately established the correlation between radon and lung cancer. (Dunford, 1991) As long as the atmosphere dilutes radon, the cancer is insignificant.
Near ground level there is no more than about one radon atom for every 10,000,000,000,000,000,000 atoms of air. The problem is, it seeps into buildings and homes where it becomes trapped, and consequently accumulates. The EPA estimates that as many as 8 million homes may be harboring unacceptable quantities of radon. Other experts believe this figure to be much higher. One study concluded that radon exposure in the home could be linked to some 9,000 incidents of lung cancer annually. The EPA goes on to say that they believe 10% of all lung cancer fatalities in the United States are caused by this problem. (Dunford, 1991)
There are a number of ways radon gas can enter a house. It usually seeps in through foundation cracks, sumps, floor drains, floor/wall joints, basement windows, and sometimes it can penetrate a sound foundation and/or solid concrete walls, since even they are somewhat porous (Dunford, 1991). Radon may also occasionally enter in through the water supply. The EPA estimates that as much as 5% of the radon exposure in the average house originates from this source. In addition, as many as 1,000 Americans die annually because of it.
Those states who have been found to have unsafe radon levels are Maine, Illinois, California, Idaho, Montana, Oklahoma, Pennsylvania, Kansas, Maryland, New Jersey, New York, Missouri, Wisconsin, and Texas (Dunford, 1991). One town, Clinton, New Jersey contains a subdivision of homes built on a ridge next to a limestone formation that is radioactive. Also, an extensive deposit of uranium-laden granite called the Reading Prong, through parts of New Jersey, New York, and Pennsylvania, including about 100,000 homes, has proven to be one of the worst areas.
Also on an alert list are regions that were former mining areas where uranium tailings also exist such as Florida, Tennessee, and Colorado. Some of these tailings were once used not only for building materials, but for landfill as well. Grand Junction, Colorado has been particularly plagued with this problem. (Dunford, 1991)
The state of Iowa has been identified recently as having unsafe radon levels. The EPA was astounded to learn that as many as 71% of homes tested in early 1989, exceeded safe levels.
Tests completed by the EPA in the fall of 1989 have even turned up astonishingly high radon levels in other states, too- namely Georgia, Ohio, Vermont, New Mexico, West Virginia and Alaska. (Dunford, 1991)
There are a number of testing options. Some include the use of a variety of expensive laboratory instruments used by commercial businesses. Most give readings in working levels (WL), which is the unit of measurement for radon decay products. Fees vary when professionals take measurements using these machines. Readings may not always reflect an accurate average, though, because such mechanisms are not only intended for short term testing, but in some cases are sensitive to weather conditions or excessive dust (James Long-EPA, 1998).
Radon is an interesting but difficult element to study. Because it is impossible to detect using only the human senses, it often causes serious and devastating illnesses in many communities. Radon is also a difficult element for scientists to study because of it’s radioactivity. Radon is important to understand because of the risks it causes to your health. If you are familiar with this element you will know to test it and keep yourself and others safe. I would still like to know more information on the positive role that radon plays in science and medicine. This information was scarce and very difficult to locate.