Detecting Cosmic Rays by Radar

Around the end of January 2011, a new scientific instrument should be operating in Delta, detecting mysterious subatomic particles from space. It will be “the world’s first radar observatory for cosmic rays,” said John Belz, research associate professor in physics and astronomy at the University of Utah.

Belz spoke Wednesday evening during a “Science Night Live!” presentation at Keys on Main, 242 S. Main, sponsored by the U.’s College of Science. Scores of people were present. University officials said the talk drew more attendees than any other in the series.

[John Belz, U. of U. astrophysicist, discusses cosmic rays Wednesday night, pointing out information on a screen. The lecture is watched by Pierre Sokolsky, dean of the College of Science, and others. Photo by Cory Bauman]

Cosmic rays are not literally rays but atomic nuclei that dart through space at nearly the speed of light. They continually bombard Earth, several passing through everybody every minute. Some of these particles reach energy states never replicated in laboratories, although their minuscule size makes them relatively harmless.

Worldwide, a main thrust of cosmic ray research is to determine the source of the most energetic examples. Their origin has been controversial for decades, with theories ranging from a cyclotron effect around certain stars, to material spewed from the torus of matter and energy that shoots out from the vicinity of black holes in other galaxies.

The radar observatory would be part of a much larger cosmic ray experiment called the Telescope Array, based in Millard County. Collaborating institutions are in Japan, Korea, Russia, China, Taiwan and the United States.

For several years, three stations in the Telescope Array have been conducting “air fluorescence” studies, in which flashes triggered by cosmic ray showers in the atmosphere are recorded by sensitive photomultiplier tubes. Meanwhile, more than 500 “ground array” instruments are measuring charged particles when they reach the surface.

[One of the ground-array detectors in the Millard County desert. Photo by Joe Bauman]

Besides the systems already in place across the Millard County desert, another way to detect cosmic rays may be through radar, Belz said. When cosmic rays slam into molecules in the atmosphere, a cone of shocked air becomes ionized. This ionization will reflect radio waves, the just as a speeding car reflects radio waves to an officer’s radar gun.

(Radar uses high-frequency radio waves; when the technique was invented in 1940 it was given the acronym RAdio Detecting And Ranging.)

Under the plan, a transmitter in Delta will broadcast radio waves while a receiver 30 miles away listens for the echoes of cosmic rays that encounter the signal. Scientists hope the radar reflections will help determine such features as the rays’ direction, mass and speed at entering the atmosphere.

Potentially, this information could pinpoint the sources of some of the particles.

Radio reflections have been used to detect meteors in the atmosphere, as the bits of material burn up and ionize their surroundings. Experimenters were able to piggyback on transmitters sending out TV shows.

As he prepared to play back the sound from such a radio experiment, Belz said, “We’re going to hear a lot of static and … the high-pitched pings of radio waves bouncing off meteor trails.” Most of the meteors are the size of grains of sand, he said. The radio sounds carry information about the meteor’s direction and its speed relative to the receiver.

Over a speaker came gritty static broken by the eerie high-pitched howls of disintegrating meteors.

Next he played what he termed a candidate cosmic ray signal, which was captured during a meteor shower. The recording sounded like meteor noise, except that in the middle a sharp “click!” erupted, apparently caused by a cosmic ray striking the atmosphere.

With last year’s nationwide shift in television broadcasting from analog to digital transmissions, many analog transmitters became surplus. The university acquired one from the Salt Lake TV station KUTV.

Instead of sending out TV images, which for scientific purposes would be a muddled transmission, the observatory will broadcast “what you would call just a continuous tone” around 54 megahertz. The receiver will be “at one of our fluorescence sites on the opposite side of our ground array.”

Asked by Nightly News when the radar detector will be working, he said, “We’ve got the transmitter working in the basement of the Physics Building now, and we’re trying to prepare the transmitter building and also our receivers so that by the end of January we’ll be on the air and hopefully collecting some interesting data.”

[Julie Callahan, an outreach specialist for the National Science Foundation, operated this cloud chamber during the "Science Night Live!" The device shows the tracks of particles, simulating the way subatomic particles from space may be detected by radar. Photo by Joe Bauman]

What will the radar observatory discover? Nobody can be certain until the experiment begins.

“There are some challenges to be met,” Belz said, “but if we knew what we were doing it wouldn’t be called research.”

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