Answer to Question #1617 Submitted to "Ask the Experts"

Q

How much radiation is emitted from a human being? People who receive medical radiation procedures would obviously emit a great deal of radiation, but what about an average member of the public? Is this emitted radiaton primarily caused by internal radioactive isotopes, ⁴⁰K and radon, or is there another source?

A

Potassium-40 (⁴⁰K) is the primary source of radiation from the human body for two reasons. First, the ⁴⁰K concentration in the body is fairly high (about 2 pCi per gram of soft tissue). As a ballpark estimate, there are 200,000 disintegrations of ⁴⁰K per minute in a typical human. Second, ⁴⁰K emits gamma rays in a little over 10% of its decays and most of these gamma rays escape the body. In other words, the body emits close to 20,000 gamma rays per minute from ⁴⁰K. The vast majority of the beta particles that ⁴⁰K emits do not escape the body. There are many other radionuclides in the human body but these are either present at lower levels than ⁴⁰K (for example, ²³⁸U, ²²⁶Ra, ²¹⁰Pb, ²¹⁰Bi, ²¹⁰Po, etc.) and/or they do not emit gamma rays (for example, ³H and ¹⁴C). Radon (and its decay products) is not a significant source of radiation because it is present at very low levels in the body. There is one other (very minor) mechanism by which the human body acts as a source of radiation: some of the gamma rays emitted by the radionuclides in the environment interact with the atoms in our bodies by what is known as the photoelectric effect. The result is the emission of x rays by these atoms. Paul Frame, CHP, PhD