A LIVING RADON REFERENCE MANUAL Robert K. Lewis Pennsylvania Department of Environmental Protection Bureau of Radiation Protection, Radon Division and Paul N. Houle, PhD University Educational Services, Inc. Abstract This “living” manual is a compilation of facts, figures, tables and other information pertinent and useful to the radon practitioner, some of which can be otherwise difficult to find. It is envisioned as a useful addition to one’s desk and radon library. This reference manual is also intended to be a “living” document, where its users may supply additional information to the editors for incorporation in revisions as well as updates to this document on-line. Topics contained within the current version include radon chemistry and physics, radon units, radon fans, epidemiology, ambient radon, diagnostics, dosimetry, history, lung cancer, radon in workplace and radon statistics. In some cases motivations and explanations to the information are given. References are included. Introduction This reference manual is a compilation of facts, figures, tables and information on various aspects of radon science. It is hoped that this manual may prove useful to federal and state employees, groups such as AARST and CRCPD, and industry. There are numerous other reference manuals that have been produced on the various aspects of radon science; however, we hope that this manual will have a more “applied” use to all of the various radon practitioners who may use it. Many of the snippets on the various pages are highlights from referenced sources. The snippet will obviously only provide one with the briefest of information. To learn more about that item go to the reference and read the whole paper. It is our intent to continually update this manual with the help of all those mentioned above. Especially helpful would be remarks, comments and additions to the manual from anyone inclined to help. Please forward any contributions to Table of Contents Introduction............................................................................................................... 1-1 Chemistry.................................................................................................................. 2-1 Physics...................................................................................................................... 3-1 Units ......................................................................................................................... 4-1 Derivation of Rn/Tn working level............................................................................ 5-1 Radon-222 Dose Calculation..................................................................................... 6-1 Dosimetry ................................................................................................................. 7-1 Effective Whole Body Dose Equivalent (EDE) ......................................................... 8-1 Risks From Indoor Radon-US EPA........................................................................... 9-1 Radon-222 and Lung Cancer Risk Estimates ........................................................... 10-1 Epidemiology.......................................................................................................... 11-1 Lung Cancer............................................................................................................ 12-1 Lung Cancer Rate by State ...................................................................................... 13-1 NCRP Pie Chart ...................................................................................................... 14-1 History of Radon-222 Occupational Limits ............................................................. 15-1 Radon Geology ...................................................................................................... 16-1 Radon Decay Products ........................................................................................... 17-1 Radon Variability.................................................................................................... 18-1 Radon in the Workplace .......................................................................................... 19-1 Diagnostics ............................................................................................................. 20-1 Fan Selection .......................................................................................................... 21-1 Fan Comparison ...................................................................................................... 22-1 Post-mitigation Radon Data..................................................................................... 23-1 Ambient Radon ....................................................................................................... 24-1 Radon Statistics....................................................................................................... 25-1 State Radon Data..................................................................................................... 26-1 State Radon Rankings ............................................................................................. 27-1 EPA State Rankings ................................................................................................ 28-1 PA Radon Analyzer Data vs. UK Data .................................................................... 29-1 International Radon Section .................................................................................... 30-1 10 CFR 20 Table..................................................................................................... 31-1 Other Radon Reference Manuals ............................................................................. 32-1 Radon in Water .............................................................................................In Progress Radon and Granite/Building Materials ..........................................................In Progress Radon Testing Equipment/Devices................................................................In Progress Mitigation Equipment ...................................................................................In Progress Thoron ..........................................................................................................In Progress Pertinent Web Sites .......................................................................................In Progress September 14, 2009 98 Chemistry of Radon Atomic Number: 86 Symbol: Rn Atomic Weight: 222.0176 Discovery: Fredrich Ernst Dorn 1898 or 1900 (Germany) discovered the element and called it radium emanation. Ramsay and Gray isolated the element in 1908 and named it niton. Word Origin: from radium. Radon was once called niton, from the Latin word nitens, which means “shining.” Isotopes: At least 20 isotopes of radon are known. Radon-220 is commonly called “thoron” and emanates naturally from radium-224, one of the decay products of thorium-232. Thoron is an alpha-emitter with a half-life of 55.6 sec. Radon-219 is commonly called “actinon” and emanates from radium-223, a decay product of actinium-227. It is an alpha-emitter with a half-life of 3.96 sec. Properties: Radon has a melting point of -71° C, boiling point of -61.8 °C, gas density of 9.73 g/l, specific gravity of the liquid state of 4.4 at -62°C, specific gravity of the solid state of 4 and usually a valence of 0 (it does form some compounds, however, such as radon fluoride). Radon is a colorless gas at normal temperatures. It is also the heaviest of the noble gases. When it is cooled below its freezing point it displays brilliant phosphorescence. The phosphorescence is yellow as the temperature is lowered, becoming orange-red at the temperature of liquid air. Inhalation of radon decay products presents a health risk. Radon build-up is a health consideration when working with radium, thorium or actinium. It is also an issue in uranium mines. September 14, 2009 99 Sources: It is estimated that each square mile of soil to a depth of 6 inches contains approximately 1 g of radium, which releases radon to the atmosphere. The average concentration of 21 radon is about one in sextillion parts of air (1 radon atom in 10 air atoms.). Radon naturally occurs in some spring waters. Element Classification: Inert Gas Density (g/cc): 4.4 (@ -62°C) Melting Point (°K): 202 Boiling Point (°K): 211.4 Appearance: heavy radioactive gas Specific Heat (@20°C J/g mol): 0.094 Evaporation Heat (kJ/mol): 18.1 First Ionizing Energy (kJ/mol): 1036.5 Lattice Structure: Face-Centered Cubic References: Los Alamos National Laboratory (2001), Crescent Chemical Company (2001), Lange's Handbook of Chemistry (1952), CRC Handbook of Chemistry & Physics (18th Ed.) and http://chemistry.about.com/od/elementfacts/a/radon.htm September 14, 2009 100 Physics of Radon Atomic and Nuclear Structure Let’s first recognize that atoms consist primarily of electrons, protons and neutrons. Interestingly, the protons and neutrons exist in a very small central region called the nucleus, while the electrons orbit outside this region at quite a distance comparatively as seen in this drawing. The number of protons in the nucleus uniquely defines the element of which the atom is a part. For example, if there is only one proton in the nucleus of an atom, that atom is a hydrogen atom, no matter how many neutrons or electrons are also part of that atom. If there are 86 protons in the nucleus of an atom, that atom is a radon atom, again regardless of how many protons or neutrons are in that atom. Radioactive decay is defined to be the spontaneous breakup of an atom. Not all atoms are radioactive and those that are not are called “stable.” If we have a group of radioactive atoms, such as radon, or uranium or plutonium, if we just wait a while, some of them will break up or explode spontaneously. Moreover, it is interesting to note that this “break up” or decay is relatively easy to model. An analysis of this decay points out that every radioactive element has a unique half-life. Half-life being defined as the time it takes for half of a sample’s atoms to decay to the next nuclide in the decay chain. For example, U-238 is radioactive with a half-life of 4.47 billion years. This means if you have 1000 U-238 atoms in your hand today and wait 4.47 billion years you will have only 500 U-238 atoms in your hand, and in another 4.47 billion years, you will then have only 250 U-238 atoms in your hand. All right, so there’s a slight problem here in having you live that long, but you get the point. If we take Radon as an example, its half-life is 3.82 days. Therefore, if you have 1000 radon atoms in your hand today, in 3.82 days you will have just 500 radon atoms and in September 21, 2009 101 another 3.82 days, or a total of 7.64 days, you will have 250 atoms. The graph below depicts this decay rate. This is also sometimes called exponential decay, simply because the number of radon atoms N(t) existing at the time t is given by the equation: ��t Where Ni is the number of radon atoms existing initially at t = 0, λ is the decay constant, or the probability of decay per unit of time (e.g. 2 per second, or in this case 0.181 per day) and t is the time as measured from when the initial number Ni exist. Notice from the graph and the equation above that the number of radon atoms is predicted to go to zero only after a very long time. Actually, after the number of atoms decreases to a small number, the statistical assumptions leading to the concept of half-life fail. Fortunately, one very rarely comes upon situations where the number of atoms is that small. Distribution of the Heavy Elements Uranium is a common element found almost everywhere within both the earth’s crust and seawater in varying concentrations. N (t) = N � exp # of radon atoms vs. time In nature, uranium atoms exist as uranium-238 (99.284%), uranium-235 (0.711%) and a 1000 very small amount of uranium-234 (0.0058%). Uranium decays slowly by emitting an alpha particle. The half-life of uranium-238 is about 4.47 billion years and that of 800 uranium-235 is 704 million years, making them useful in dating the age of the Earth. 600 There are four decay chains of importance when considering naturaly ocuring i radioactive materials, each defined by its heaviest natural (not man-made) element. 400 These are the U-235 series (also called the Actinium Series), the thorium-232 series (the Thorium Series), the U-238 series (the Uranium Series) and the Np-237 series (the 200 0 September 21, 2009 0 1 2 3 4 5 6 7 8 9 10 102 time (days) # of radon atoms Neptunium Series); graphical depictions of each are shown below. The one of most interest to us is the decay chain that includes radon-222, namely the U-238 series. -6 -3 6 9 1µs = 10 s, 1 ms = 10 s,1 My = 10 y, 1 Gy = 10 y September 21, 2009 103 -6 -3 6 9 1µs = 10 s, 1 ms = 10 s,1 My = 10 y, 1 Gy = 10 y September 21, 2009 104 -6 -3 6 9 1µs = 10 s, 1 ms = 10 s,1 My = 10 y, 1 Gy = 10 y September 21, 2009 105 -6 -3 6 9 1µs = 10 s, 1 ms = 10 s,1 My = 10 y, 1 Gy = 10 y The members of this series are not presently found in nature because the half- life of the longest-lived radionuclide in the series is short compared to the age of the earth. Further, this chain does not include an isotope of radon. Reference: http://hyperphysics.phy-astr.gsu.edu/HBASE/hframe.html September 21, 2009 106