Radiation in Boulder County
By Richard Hollos and Stefan Hollos

June 23, 2006

You may have heard that being at higher altitudes increases your radiation exposure. Here in Boulder County, we live at a higher altitude than much of the nation. How does this affect you? You may have also heard about radon, a source of radiation indoors. Do you know what every Boulder County resident should know about radon?

What is Radiation?

The Merriam-Webster dictionary defines radiation as "the process of emitting radiant energy in the form of waves or particles". When we talk about radiation here, we will use a more restrictive definition: particles or waves with enough energy to remove electrons from matter.

Electrons are particles that surround the core of each atom, the nucleus. Practically everything you are familiar with is made out of electrons - from the phone you used to make hotel reservations to the mouse you're holding while you navigate this site. When something has enough energy to remove electrons, it is said to be capable of ionizing. The waves in our definition of radiation are electromagnetic waves, the same type of waves as visible light, but higher in energy. These higher energy electromagnetic waves have a number of names depending on how high their energy is. The waves we will be talking about here, in order of increasing energy are: ultraviolet, x-ray, and gamma ray. The particles in our definition of radiation are primarily high energy electrons called beta radiation, and high energy helium nuclei called alpha radiation. From a practical standpoint, when a particle or wave has enough energy to ionize, it can cause damage to your body.

Radiation from Space

A significant portion of radiation that we are exposed to on the surface of the Earth originates from space. Most of this radiation comes from the Sun, which is continuously bathing the outer edge of our atmosphere with an energy of 127 Watts per square foot. This energy from the Sun includes visible light, ultraviolet light, x-rays, gamma rays, and protons (a proton is the nucleus of a hydrogen atom). But thanks to our protective atmosphere, the most harmful forms of this energy are filtered out, leaving only 28% of the original energy to fall on the surface of the Earth, in the form of visible and some ultraviolet light. The ultraviolet portion has sufficient energy to be considered ionizing radiation.

The Sun's output can suddenly change, during what are called "solar storms", blasting the top of our atmosphere with shock waves of intense radiation which can be fatal to astronauts, but thankfully here on the surface of the Earth this variability is mostly damped out, resulting in an insignificant increase in our radiation exposure. For more information about solar storms see the Boulder Colorado based Space Environment Center's website. The Sun's output also varies long term over its approximately 11 year cycle, during which time its output reaches a maximum when the number of sunspots reach a maximum, and its output reaches a minimum when the number of sunspots reach a minimum. The total variability in the solar output, though, is never greater than 0.2%, making the sun actually a remarkably stable source of radiation.

Another source of radiation from space originates from outside our solar system. This consists primarily of the nuclei of light atoms such as hydrogen and helium, and less frequent heavier nuclei and gamma rays. This radiation tends to be much higher in energy than that coming from the sun, and is therefore more destructive. Luckily, it is not as frequent as that coming from the sun. When this high energy radiation reaches the outer edge of our atmosphere, it soon collides with an atom, breaking it apart, whose pieces in turn break more atoms apart. The result is that in a fraction of a second, a shower of millions of particles, mostly electrons, reaches the surface of the Earth. This is yet another source of radiation that you are exposed to.

Radiation from the Ground

Radiation from the ground is due to certain radioactive elements found there. Radioactive elements are unique in that they behave as though each atom has a clock inside that is winding down to zero. When its time runs out, the atom explodes or decays, breaking into pieces. Some of these pieces such as electrons (beta radiation) and helium nuclei (alpha radiation) move at such high speeds that they can ionize things that they hit. There is usually also a heavier piece remaining that is a different element from the original, and which is often also radioactive. The amount of time on the "clock" of a radioactive element when it is born is related to a quantity called the halflife of the atom.

Here in Boulder County, the ground is the single biggest source of radiation. This is due to the high content of the radioactive elements uranium and thorium in the soil originating from eroded granite. Parts of the northwest quadrant of Boulder County in particular contain high amounts of thorium, and there is a uranium mine, the Schwarzwalder mine, in nearby Jefferson County, 8 miles northwest of Golden.

As the uranium and thorium in the ground decay into other elements they eventually become element number 86, radon. Radon is more dangerous than the other elements in the decay process because it is the only one that is a gas. The radon therefore tends to leak out of the ground, and can build up into dangerous concentrations in your home, especially in underground areas such as basements. Mixed in with normal air, this radon, with a halflife of only 3.8 days, breaks down into polonium-214 and polonium-218. Radon itself is chemically unreactive, but its decay product polonium is chemically similar to oxygen and can accumulate in the lungs when inhaled. When the radioactive polonium breaks down, alpha radiation is emitted and damages your lungs. This lung damage can eventually lead to lung cancer. According to John Barbour of the Boulder County Health Department, 42% of Boulder County homes have radon concentrations above the level that the EPA considers safe.

How are Boulder County residents affected?

You can get an estimate for how much radiation you are exposed to over the course of a year from the online radiation dose calculator at Los Alamos National Lab. For example, a nonsmoking Boulder/Longmont area resident living at an elevation of about 5,300 feet will have an estimate something like this:

Radiation Dose Breakdown for Boulder/Longmont
Cause of RadiationAmount of Radiation [mrem]
Air (radon, average U.S.)200
Food & Water (average U.S.)40
Wood house2
TV & Computer monitor2
Weapons test fallout1

Therefore the total radiation exposure estimate for a Boulder/Longmont resident is 390 mrem. The unit of mrem is a thousandth of a rem, which is an abbreviation of roentgen equivalent man, being a measure of the amount of ionizing radiation absorbed by biological tissue. Comparing this estimate to a Florida resident living near sea level, a Boulder/Longmont resident gets about twice as much radiation due to elevation, and three times as much radiation due to the ground.

Does this higher radiation from both elevation and the ground lead to higher cancer rates for Boulder County residents compared to the national average?

How does the cancer rate in Boulder County compare to the national average? The increased radiation due to our higher than average elevation would probably show up as a higher incidence of skin cancer, since ultraviolet radiation increases with altitude. Melanomas of the skin incidence rates per 100,000 for the entire U.S.A. over the years 1993 to 1997 are 14.4 for males and 9.4 for females. For Boulder County residents the incidence rates over the years 1995 to 1998 are 19.8 for males and 18.0 for females. Therefore Boulder County residents do have significantly higher skin cancer rates than the national average which agrees with the expectation.

Higher radon concentrations, than much of the nation should show up as a higher incidence of lung cancer. Lung cancer incidence rates per 100,000 for the nation is 78.8 for males and 44.4 for females over the years 1993 to 1997. For Boulder County residents it is 52.9 for males and 37.1 for females over the years 1995 to 1998. Therefore, Boulder County residents have lower lung cancer rates than the national average. This contradicts the expectation of higher lung cancer rates due to higher radon levels. It may be possible that other factors are involved in this contradiction, like Boulder County residents being more physically active, or smoking less than the average American.

What can you do?

Considering the high incidence of melanomas of the skin in Boulder County, it is very important to protect yourself from ultraviolet radiation. Be sure to follow the advise of dermatologists in minimizing ultraviolet exposure.

How can you find out if radon is a problem in your home? Test kits which you can send in for laboratory evaluation are available for about $15. Home inspectors can test for radon for about $75. Electronic radon detectors can be purchased for about $100.

About the Authors: Richard Hollos and Stefan Hollos are Physicists at Exstrom Laboratories LLC in Longmont. They design scientific instruments and do physics research there.

For further information

Online radiation dose calculator at Los Alamos National Lab

Boulder County Radon Program website

EPA Radon Homepage

Report: Cancer in Colorado, 1993-1998: Incidence and Mortality by County, Colorado Department of Public Health and Environment

Space Environment Center website

Radioactivity in Nature website at Idaho State University

Nearest star : the surprising science of our sun by Leon Golub and Jay M. Pasachoff Publisher: Harvard University Press Date: 2001., 267 pages

The sun-earth system by John Streete Publisher: University Science Bks Date: 1996, 34 pages

Sun, earth, and sky by Kenneth R. Lang Publisher: Springer-Verlag Date: 1995, 282 pages

Living with radiation: the risk, the promise Henry N. Wagner, Linda E. Ketchum Publisher: Johns Hopkins University Press Date: 1989, 193 pages

Nine Crazy Ideas in Science: A Few Might Even Be True by Robert Ehrlich Chapter 5: Low Doses of Nuclear Radiation Are Beneficial Publisher: Princeton University Press Date: 2001, 288 pages

Environmental radioactivity : from natural, industrial, and military sources by Merril Eisenbud and Thomas Gesell, 4th ed Publisher: San Diego : Academic Press Date: 1997, 656 pages

Fundamentals of atmospheric physics by Murry L. Salby Publisher: San Diego : Academic Press Date: 1996, 627 pages

Atmospheric processes and systems by Russell D. Thompson Publisher: London ; New York : Routledge Date: 1998, 194 pages

A thin cosmic rain : particles from outer space by Michael W. Friedlander Pubisher: Harvard University Press Date: 2000, 241 pages

For more information contact:
Richard Hollos
richard[AT]exstrom DOT com
(303) 678-1487

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