Concrete also has natural background radiation from thorium and uranium oxides in the original crushed limestone (I have measured these materials in limestone using XRD). Fly ash (from burning coal) has a lot more of these materials as an earlier post indicated. Similar natural sources of radiation include potassium (both from food and granitic rock) and from outer space during solar minimums such as at present. It's probably a good source of genomic mutations, some good, some not so good.
- Jill


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