Messages by Muons

In the realm of high-energy physics, muons can be an outright nuisance. These tiny atomic fragments, somewhat heavier than the electrons they resemble, are produced when protons collide inside the bowels of large atom smashers. They live for only a fraction of a second, but are able to pass unscathed through heavy barriers or shields. Thus, unless carefully controlled, they often show up where they are not wanted, and can play havoc with experiments. Now a scientist at the AEC's Argonne National Laboratory outside Chicago plans to put the troublesome particles to work. In an effort to take some of the burden off the increasingly crowded air waves, Theoretical Physicist Richard C. Arnold proposes using beams of muons as the core of a radical new communications technology that could supplement and even replace some standard radio signals.

What would make muons so useful as messengers is the very characteristic that sometimes annoys experimental physicists: their ability to penetrate barriers. Radio waves--especially the increasingly popular microwaves, which require line-of-sight transmission between relay towers--are essentially blocked by buildings, hills and other obstructions. Thus the ghostly muons could be highly useful in heavily built-up metropolitan areas, where they would easily reach into the interior of metal skyscrapers and even deep into subway tunnels. What is more, since muons travel in a relatively narrow beam, they could be aimed with precision. Says Arnold: "You wouldn't have to worry about sending signals where you didn't want them."

Arnold is convinced that his scheme is entirely feasible. As a demonstration, he reports in Science, he recently set up two detectors near Argonne's 12 billion-electron-volt proton synchrotron. Then he periodically inserted a small block of brass in the path of a beam of particles from the accelerator. The effect was predictable: whenever the metal was in the way, it slightly weakened but did not block the flow of muons to the detectors 160 yds. away. Arnold had in effect devised a simple Morse telegraph system. By appropriately timing the intervals during which the metal was in the beam, he could, for instance, send the letter V (dot-dot-dot-dash). With a more complex system, Arnold explains, a muon beam could be sufficiently modulated to carry complete Teletype messages, voice conversations and perhaps even television images.

Radiation. At present the only method man has for producing muon beams of message-carrying strength is to use expensive atom smashers. But Arnold contends that less costly machines designed specifically to make muons could be built in the near future. According to his estimate, a 100 billion-volt synchrotron, capable of producing a muon beam with a range of up to 600 miles, would cost about $10 million. That is roughly the price of a system of microwave towers covering a comparable distance. Furthermore, Arnold says, there might actually be a savings if muon beams were used to take some of the load off communications satellites. Aimed beyond the earth's atmosphere, a muon beam would be bent down toward the surface again by the earth's magnetic field and could be detected hundreds of miles from its point of origin.

Arnold concedes that possibly harmful radiation from such beams might be a cause for concern, but it need not be an insurmountable problem. The beams could be somewhat spread to reduce their intensity to a safe level, yet still retain enough strength to carry messages.

Muon transmissions may point the way to a more dazzling form of communication. The large "zoo" of subatomic particles, as physicists call it, includes an even stranger will-o'-the-wisp called the neutrino: a virtually massless and chargeless bundle of energy. That tiny particle can pass through matter of any thickness, including the entire earth. Furthermore, regardless of how many neutrinos there might be in a beam, they would present no radiation hazard. Thus if a neutrino transmission and detection system could be developed, the elusive particle might prove to be an even better answer to man's growing communications needs.

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