Answer to Question #11287 Submitted to "Ask the Experts"

Category: Environmental and Background Radiation — Soil and Fallout

The following question was answered by an expert in the appropriate field:


I have read Question 8457 and the answer regarding residual radioactive elements in southern Utah. I have a closely related yet different question: Are there still long-half-life elements present in that general area or even around the United States in general that could be picked up on one's shoes or clothing and unintentionally carried away from the area?

We are considering a visit to Zion National Park and also to Bryce Canyon, and though it may sound a bit crazy, the possibility of such exposure worries me. What can you tell me about this possible hazard?


Your worries about radiation are normal. Most everyone today is afraid of radiation based on news stories promoting radiation as something to fear. We also tend to be more afraid of potential dangers that we don't know much about, and most people do not have good information about radiation.

In response to your concerns about visiting Zion National Park and Bryce Canyon, I note that you have already looked at the response to a similar question (Question 8457), and therefore you know where to find information from websites of the U.S. Environmental Protection Agency and the U.S. Geological Survey.

The two radionuclides of most interest from nuclear weapons fallout are strontium-90 (90Sr) and cesium-137 (137Cs). These radionuclides each have half-lives of about 30 years. Thus, from any original fallout only about one-quarter would remain today. In addition, over the past 60 years these radionuclides would have migrated into the soil and little, if any, would remain on the surface.

You may also understand that all soil contains radioactive elements of uranium, thorium, radium, and potassium. These elements are found in soil everywhere as naturally occurring radioactive materials (NORM). Thus any soil that you pick up on shoes or clothing will be radioactive from NORM, regardless of any residual fallout. Your exposure to radioactive materials due to NORM in soil is likely about the same in Utah as in most Rocky Mountain states, although some areas may have more or less uranium or radium depending on the geology of the soil.

Since you cannot avoid exposure to NORM no matter where you live, I encourage you to visit the parks and enjoy the wonders of nature.

Ray Johnson, MS, PE, PSE, FHPS, CHP

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
Answer posted on 24 August 2015. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.