X Rays in the Living Room

Most people know that they can get a severe electric shock if they recklessly poke into the back of an operating TV set, where high-voltage components are placed out of harm's way. But until recently, few were aware that the same high voltages may pose a more subtle threat: they can produce X rays that, if improperly shielded, endanger viewers sitting unusually close to the set.

The X ray-producing potential of TV sets first came to public attention in May, when the General Electric Co. announced that it had discovered excessive X-ray emissions from some of its large-screen color TV sets. To eliminate any danger, G.E. said that it was replacing an improperly shielded voltage regulator tube in more than 100,000 color TV sets (18-, 20-, 22-and 23-in.) that were sold between Sept. 1, 1966 and May 31, 1967. But 9,000 of the G.E. sets have not yet been located. The U.S. Public Health Service has now urged anyone who owns one to disconnect it until the faulty tubes have been replaced.*

Lethal Leak. Any vacuum tube operating at several thousand volts or more produces detectable X rays. Boiling off the incandescent cathode of the tube, electrons are attracted and accelerated by the high positive voltage on the tube's anode and smash into it at great speed. Struck by the electrons, the atoms of the metallic anode vibrate violently and emit energy in the form of X rays, which can burn the skin, injure the eyes and cause genetic damage.

To reduce X-ray emissions of high voltage tubes to safe levels, manufacturers equip the tubes with metallic shields that absorb most of the radiation. But because of a manufacturing error, the shields inside many of the 24,500-volt G.E. tubes were misaligned. As a result, part of the X rays emitted by the anode could leak through the bottom of the tube. The radiation from the tube, according to the Public Health Service, ranged from ten to 100,000 times more than the rate considered safe.

Danger in 60 Minutes. Because the radiation was directed downward, P.H.S. officials noted that most viewers would probably not be harmed. But they worried about children sitting on the floor near TV sets placed on tables or shelves. X rays shooting through vents in the bottom of such sets could produce serious eye damage within an hour. Because the effects of X rays are cumulative, many hours of exposure at greater distances from an elevated set could also be dangerous.

G.E. has long since corrected its voltage regulator tubes by extending their internal shielding and enveloping them in leaded glass. According to a G.E. study, X rays emitted by the faulty tubes were sufficiently absorbed by other components and the cabinet to reduce the outside radiation to harmless levels. But G.E. and the Public Health Service will breathe easier when the last of the 9,000 missing sets has been located and its menacing tubes replaced.

* Says G.E.: "The color sets to be modified have a blue 'fine tune' gauge above the control knob and, on the back of the set, either a serial number beginning with OA or OD or no serial-number sticker at all. Receivers that have already been modified have a red and white label pasted on the back."

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