“How many of you who moved to Colorado from Texas or Florida took into account that you were nearly tripling your annual dose of natural radiation by studying here?” That is the first question I ask students in my radiation biology class at Colorado State University, and of course none of the students considered that they were increasing their exposure to radiation by a large factor simply by moving here to live. And none of them would have used that as a reason to not study here. In contrast, if they were moving near a nuclear power plant in their state, they might have had second thoughts, even though they would be exposed to far less radiation than by coming to Fort Collins, Colorado.

There is no place on earth where you are not exposed to radiation. As I said in the previous chapter, life evolved in a radiation environment. But where does the radiation come from, and why is it higher in Colorado than elsewhere in the United States? Are there other areas in the world where it is even higher? Do we get a lot more cancer in Colorado than in other lower radiation states because we are exposed to more radiation? These are important questions—they help us to understand the risk from a particular dose of radiation and put into perspective the exposure to radiation from the nuclear fuel cycle.

We are exposed to radiation that comes from the skies, from the earth, and from our food. These are all natural sources, and there is not much we can do about it except decide where we want to live. But our decisions as to where we want to live almost certainly do not take into account the exposure to background levels of radiation from natural sources. The other main not-so-natural source of radiation exposure comes from medical procedures, a source that is increasing rapidly.

The National Council on Radiation Protection and Measurements (NCRP) publishes scientific information on radiation and its hazards, as well as protec­tion guidelines to assure that workers in radiation environments and the general public are safe. One of the NCRP reports details the exposure of the average US citizen to background radiation. In 1987, 83% of the exposure came from natu­ral sources of radiation, with only 15% coming from medical treatments (NCRP

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Report 93). By 2006, however, medical exposures were 48% of the average dose to an individual in the United States (Figure 8.1) (1). The average US citizen gets 6.2 mSv (620 mrem) of radiation every year, but of course the dose any individual gets varies from that because of where the person lives and the number and kind of medical radiation procedures the person has.