The Neon Warning

Fiddling with elaborate detectors, Lieut. Walter Johnson, 29, of the Navy's medical corps, was measuring the power density of microwave radiation from radar beams aboard the guided-missile cruiser Galveston. All at once he felt a slight burning sensation in his backside. Dr. Johnson happened to have a couple of neon lamps (the size of flashbulbs) in his hip pocket. With no wires or other connections, the lamps had glowed and heated up when he got in the way of radar waves.

As a result of Dr. Johnson's experience, crewmen of Galveston (and ships being similarly equipped) are now protected against overexposure to high-energy radar beams by a simple device: on his uniform, each man has a little neon lamp, which glows when he is exposed to danger. At the warning glow, all he has to do is step aside, out of the beam's path.

Soon after Galveston was commissioned last year, it became clear that her electronic batteries confronted crewmen with new hazards that had not shown up in earlier missile cruisers (Boston and Canberra) with lower-powered transmitters. Also, the danger of intense microwaves (TIME, April 6) had not been plotted in detail. From animal experiments and sketchy data on humans, the Navy medics set a level of 10 milliwatts per square centimeter of body surface as conservatively safe for personnel aboard missile ships. Dr. Johnson's findings on Galveston proved that this level was sometimes exceeded.

By happy chance, it turned out that the neon lamps light up when exposed to radar waves with a power density of only 5 or 6 mw. sq. cm.--about half the permissible dose for man. So they are perfect for the purpose, and last indefinitely, Dr. Johnson and two Navy medical colleagues report in the United States Armed Forces Medical Journal. Photo flashbulbs can also be used for a one-shot warning: they go off when exposed to still smaller doses of microwave radiation.

Galveston's huge radar domes, one for scanning the sky to detect enemy targets, the other for locking onto them and tracking them, at first presented another hazard: a spillover of X rays. Several men were found to have been overexposed before this fact was detected, but none have shown any ill effects. The danger was eliminated by installing extra lead shielding for the klystron tubes in the transmitters. Future tubes will be made with the shielding built in.

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