Answer to Question #8457 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 would like to know if I was exposed to any radiation and approximately how much in dose numbers, because recently I went on a road trip and I went through New Mexico and Utah. I heard that in the past, New Mexico had tested nuclear bombs and from what I understand about radiation, the Trinity Site is still radioactive, and we came within around 64 km north of that area. I was worried about any nuclear fallout from the testing. If we walked outdoors, would we have been exposed from the dust or atmosphere to anything radioactive, and could anything radioactive have clung to our skin or clothes or gotten into our lungs? If so what would be the approximate dose exposure in mrem to an individual? Where in New Mexico is it highly radioactive besides the Trinity Site, and what would be the dose from exposure? Also, where in Utah are there high levels of radiation due to nuclear fallout, and what is the exposure level in Utah?


You've packed several questions into a brief paragraph, so let me try to answer your main concerns. During your visit to New Mexico and Utah, you were not in any danger from exposure to radioactivity from nuclear fallout. The Environmental Protection Agency (EPA) has monitored radiation levels across the United States since the 1950s, when above-ground nuclear testing was in progress. Historical data show the rise of environmental radiation during nuclear weapons testing and the fall of radiation as the fallout decayed away. The EPA's website states that "since the end of above-ground nuclear weapons testing [in 1963 in the United States], the day-to-day readings from monitoring sites have fallen. Now, and for many years, analysis of typical samples shows risk levels far below regulatory limits. In fact, results are now generally below levels that instruments can detect." If our instruments can't detect elevated radioactivity from fallout, it is very unlikely that enough remains to be dangerous to your health. You can read more about the EPA's monitoring program on its website. The EPA website also discusses weapons testing fallout.

In general, radiation exposure levels from the soil in New Mexico and Utah are the same as levels throughout the Rocky Mountain region of the West. If you are interested in seeing a map of terrestrial radioactivity levels across the United States, look at the US Geological Survey's website.

But you asked specifically about the Trinity Site near Alamogordo, New Mexico, and it is true that the soil at the center of the Trinity Site is still slightly more radioactive than the surrounding soil—about 10 times greater than the region's natural background radiation. Still, that extra radioactivity results in a very small dose: if you were to stand at the center of the site for an hour, you would get a dose of about 0.01 mSv. You were not at the center of the site, but about 64 km away. Every time you double your distance from a source of radioactivity, the dose you receive from that source decreases by a factor of four. So at a distance of 64 km and assuming that the fenced-in area at the center of the site is 1.6 km across, your dose from the site was decreased by nearly 10,000! At this distance, our instruments could not measure the radiation from the Trinity Site, and any radioactive dust from the Trinity Site would have been diluted beyond detection (again, by a factor of about 10,000); it is very unlikely that these tiny amounts would present any danger to you.

Linnea Wahl, 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 21 August 2009. 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.