Thus almost all of the uranium we ingest is never absorbed but is excreted in the feces.
Of the small fraction of ingested uranium that is absorbed through the gut, most is quickly excreted in the urine and only a tiny amount is excreted in the hair. The hair from different people—or even the same person—will contain varying amounts of uranium, depending on how much is in the water and food that people drink and eat.
This is about one-tenth (or 10 percent) of the 3.1-m Sv dose that the average U. man who weighs 70 kg receives each year from all sources of natural background radiation (not including medical sources).
All of us have a number of naturally occurring radionuclides within our bodies.
The major one that produces penetrating gamma radiation that can escape from the body is a radioactive isotope of potassium, called potassium-40.
For Uranium is a naturally occurring, heavy, metallic element that is found virtually everywhere in nature—in rocks, soil, plants, and our bodies.
The average person ingests about 2 µg (around 1/15,000 of an ounce) of uranium in food and water every day, but only a very small fraction—on the order of 1 or 2 percent—is absorbed into the body.
Other types of radioactive decay (beta and alpha) cannot be detected in this way, but fortunately, gamma rays often accompany them so most can be detected.