Answer to Question #638 Submitted to "Ask the Experts"

Q

Does radiation from x rays or gamma rays stay in the body or pass through? If it stays in the body, how long does it stay? Thanks for your help.

A

Gamma rays and x rays can pass right through the body. They can also "stop" in the body. On an upcoming trip to the dentist, I expect to "receive" several x rays. The images my dentist will produce on the x-ray film are shadow pictures created when some x rays stop in the teeth and others travel through the soft tissue of my mouth to strike the film. Like alpha particles, beta particles, and neutrons, x rays and gamma rays are ionizing radiation, the type of radiation that is emitted by radioactive substances when they decay. But unlike alphas, betas, and neutrons, which are particulate matter (i.e., they possess mass), x rays and gamma rays are electromagnetic radiation. In this sense, they are more akin to visible light. And like light, they are always moving at the speed of light. It is best to think of an x ray or gamma ray as a "packet" of pure energy (called photons). What x rays and gamma rays do when they "stop" in the body, is transfer all their energy to the electrons associated with the atoms that make up the body. When an x ray or gamma ray gives up all its energy, it ceases to exist. As such, we should not think of an x ray or gamma ray as remaining in the body. On the other hand, radioactive materials which emit ionizing radiation can remain in the body for long periods of time. Each minute, over 200,000 atoms of the naturally occurring radioactive ⁴⁰K atoms in your body decay. In ten percent of these decays, gamma rays are emitted. In other words, over 20,000 gamma rays from ⁴⁰K are produced in your body each minute. The bottom line is that your body is more of a source of x rays and gamma rays than it is a "container" of them. Paul Frame, CHP, Ph.D.