Mr. Hardin stated that "X-rays, like radio waves and visible light ... do not involve neutrons at all, and are therefore called non-ionizing radiation" ("A Scream," Mailbox, March 31). While it is true that X-rays, (like radio waves and visible light), are different frequencies of electromagnetic radiation, X-rays and gamma rays will pass through our flesh and may do damage in the process. By contrast, visible light and radio waves have very little effect or interaction with our flesh.

Both X-rays and gamma rays are powerful enough to ionize air or biological cells. For example, the "Kearny Fallout Meter" (KFM) is a highly reliable (and homemade!) radiation detector that measures the rate of discharge between two charged plates using ionized air. In a radioactive environment, gamma rays and X-rays ionize the air, and these ions cause current flow in the air between charged plates of a KFM, which cause the charged plates to move toward each other.

Anyone who wants visual proof that X-rays produce ionizing radiation should persuade a dentist to place a charged KFM about 20 inches directly below a typical dental X-ray machine. When a typical 90 kvp machine is set at 15 milliamps for a 1/20th second pulse, its columnated X-ray beam partially discharges the Kearny Fallout Meter's separated aluminum-foil leaves, promptly reducing the distance between the plates by a large fraction of their total scale.

The point is that sufficiently high-frequency electromagnetic radiation will ionize air, water and flesh. There is no beneficent ionizing radiation, nor is there any "safe level" of gamma rays or X-rays. There is a simple linear relationship between ionizing radiation exposure and cancer likelihood, which has been established over the past 70 years' experience with nuclear energy. The risks posed by X-rays are, presumably, justified by the information they provide doctors, but their use has been greatly reduced as the health effects of ionizing radiation has been better understood.

John Bergamini, Eureka


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