Two Buckets of Rocks

Recent news articles claim that two buckets of rocks at the Grand Canyon Museum “overexposed” visitors to radiation. We have made radiation measurements in and around the Grand Canyon over the last two decades and routinely analyze water and soil samples from the area. We can say with assurance, that the exposure rates quoted in the article are preposterous. Natural sources, like uranium ores, don’t produce external dose rates anywhere near the values shown in the article. Even the background reading of 2 mR/hr outside of the building was impossibly high. Background in the area is 4 to 20 microR/hr. The person making the radiation measurements either chose an instrument that was not appropriate for measuring exposure rates from uranium ores, or simply read the meter incorrectly (e.g. reported mR/hr when the meter was a microR/hr meter). Most likely, he did both.