Radon was discovered by German Physicist Friedrich Ernst Dorn in1900 and was originally called "radium emanation". Radon is a colorless, odorless, tasteless, and invisible gas. It does not combine or interact readily with other chemicals or elements. Radon-222 has 86 protons in the nucleus and is found in the periodic table under the noble gases xenon, krypton, argon, neon, and helium. It is about seven times as heavy as air, is always radioactive, and emits alpha particles plus associated gamma radiation at 510 KeV. The physical half life of Radon-222 is 3.82 days. The radiobiological effectiveness of alpha particles in the lung is twenty times as great as for gamma photons.
The progeny (daughter products) of Radon-222 are all heavy metals, most with very short half lives as follows in sequential order:
The asterisks* indicate there are two alternatives for decay, and one is listed here. The final decay product, Lead-206 is still the same. Another decay route would include Thallium-206, half life 3.76 minutes*-Beta and gamma. (Z81) [RaE"] Radon-220 (Thoron, or Tn) follows a similar pattern although the half life of each decay product is shorter and there are fewer steps in the sequence. The sequential order for Radon-220 is:
- Polonium-218, half life 3.1 minutes-Alpha and gamma emitter. (Z84) [RaA]
- Lead -214, half life 27 minutes-Beta and gamma emitter. (Z82) [RaB]
- Bismuth-214, half life 19.9 minutes-Beta and gamma emitter. (Z83) [RaC]
- Polonium-214, half life 164 micro-seconds-Alpha and gamma emitter. (Z84) [RaC']
- Lead-210, half life 22.6 years-Beta and gamma emitter. (Z82) [RaD]
- Bismuth-210, half life 5.01 days-(or 3E6 years)* -Beta and gamma emitter. (Z83) [RaE]
- Polonium-210, half life 138.4 days-alpha and gamma emitter. (Z84)[RaF]
- Lead-206, stable element. (Z82) This particular isotope of lead comprises about 24% of the abundance of lead in the earth.
- Polonium-216, half life 0.145 seconds-Alpha and gamma emitter. (Z84)
- Lead -212, half life 36.1 minutes-Beta and gamma emitter. (Z82)
- Bismuth-212, half life 7 minutes (or one hour)-Beta and gamma emitter. (Z83)
- Polonium-212, half life 45 seconds-Alpha and gamma emitter. (Z84)
- Lead-208, stable element. (Z82) This particular isotope of lead comprises about 52% of the abundance of lead in the earth.
A popular pie chart used to express relative exposures from all sources in government publications demonstrates that radon is responsible for about 55% of the total exposure to the average American. All natural sources combined make up 81% of the total exposure received. However, the average total of 360 millirems (3.6 milliSieverts) per year is significantly below the amount received during a single diagnostic x-ray examination. As an average, half the population receives less than the indicated amount. Alaska has a relatively low background level of radiation. If you view the national chart of radon in the U.S., Alaska has relatively little. Using a pancake probe type survey meter a typical background reading in Anchorage, Nome or Kotzebue is on the order of 10-15 counts-per-minute, or about 0.05 mR/hour.
Here are additional links to radon information at the U.S. Environmental Protection Agency.
Also, the actual exposures received by any particular individual will vary considerably depending on where that individual lives. Denver, Colorado, is considered to have higher then average levels of exposure, while many sea level communities such as Miami have less.
Exposure to radon is often expressed in terms of Working Levels, with one Working Level equal to 1.3E5 MEv of alpha energy. 100 pCi of radon-222 per liter of air in equilibrium with its daughters equals one Working Level. A Working Level Month is based on 170 working hours per month.
The specific activity of radon-222 is 153,982 Curies/gram in pure form, or 1.54E5 Ci/gm (5.697E15 Becquerels (Bq), or 5.7 Peta Bq)(This may also be expressed as 5.967x10^6 Giga-Bq).
Radon was first associated with lung cancer in the 1920's, but it was recognized as long ago as the 1400's that miners died in the Czech Republic from working in radon environments. At that time radon was not known or considered to be the cause of their deaths.
In U.S. homes the Environmental Protection Agency (EPA) has established a recommended residential limit of 4 pico-Curies per liter (4pCi/L). The EPA estimates that 1-3% of homes exceed twice that amount, or 8 pCi/L.
Radon in Alaska
Environmental Protection Agency
© Created 2/28/2000 By Clyde E. Pearce