March 12, 1996 Contact: Robert Irion (408) 459-2495; irion@ua.ucsc.edu

UC SANTA CRUZ PHYSICIST HELPS PLAN ADVANCED GAMMA-RAY TELESCOPE

FOR IMMEDIATE RELEASE

SANTA CRUZ, CA--Stars twinkle serenely and galaxies swirl like wisps of mist when we view the universe in visible light. However, those pictures mask a violent universe of exploding supernovas, voracious black holes, and other prodigious objects. Astronomers glimpse that bizarre realm through windows of light such as x-rays and gamma rays--the most energetic light waves of all, shielded from our view by earth's atmosphere.

If funding permits, a new telescope orbiting the earth within a decade will capture gamma rays more effectively than ever before, expanding our knowledge of the violent cosmos. A group led by Stanford University has proposed the device, called the Gamma-ray Large Area Space Telescope, or GLAST. The group includes the Santa Cruz Institute for Particle Physics at UC Santa Cruz, where scientists have pioneered some of the intricate technology that will drive the satellite.

Indeed, GLAST will look more like a particle-physics detector in space than a traditional telescope. It will detect gamma rays by converting them into charged particles and then tracking those particles, with extraordinary precision, through layers of finely etched silicon. The resulting data will help astrophysicists probe the rapidly spinning stars known as pulsars, the cores of active galaxies, and mysterious "gamma-ray bursters"--intense flares of energy from sources that researchers have not yet identified.

"Our goal is to launch the telescope by 2005, which is blistering fast by NASA's standards," says project scientist William Atwood of the Stanford Linear Accelerator Center. "Interest in the project is mounting quickly. We think we can fly a prototype on a balloon flight within two to three years." Atwood, project director Peter Michelson of Stanford, and international collaborators have sent a request to NASA and the U.S. Department of Energy to fund the prototype. The full telescope may require between $100 million and $300 million to build and operate.

The team believes the telescope's promise justifies its price tag, especially because it represents a major leap ahead of EGRET, a gamma-ray telescope now in orbit. "EGRET has found unexpected things, but GLAST will be 100 times more sensitive," says Robert Johnson, associate professor of physics at UCSC. "We think GLAST has the potential to shed light on some of the most exciting phenomena in the universe."

Johnson's niche on the project is to refine the miniature electronics necessary to handle torrents of signals from the silicon detectors, which will form the heart of GLAST. Here's how the telescope will work:

GLAST will consist of 49 "towers" of silicon and other materials in a block almost six feet across. Each tower will include two dozen layers of silicon stacked like pancakes, alternating with ten thin layers of lead. When a gamma ray strikes one of the towers, the lead will convert it into a pair of charged particles--an electron and a positron. Each particle will create a track in the silicon, like the contrail of a high-altitude jet, as it zings through the rest of the layers. A final block of material, made of cesium iodide, will stop the particles and measure their energies.

Physicists will etch the silicon wafers with thousands of "microstrips" that emit tiny pulses of electricity when particles flit past. Spaced just one-quarter of a millimeter apart, the strips will pinpoint the particle tracks. GLAST scientists will then trace back along those paths to determine the exact spots in the sky where the gamma rays started their journeys across the universe. Researchers at the Santa Cruz Institute for Particle Physics and elsewhere devised this silicon microstrip technology for experiments at high- energy physics labs on earth--including the core of a detector for the now-defunct Superconducting Super Collider.

Each silicon microstrip will require its own amplifier and sophisticated memory and readout components to transfer data into the satellite's computers. GLAST poses a tough challenge to Johnson and his coworkers: The electronic components must use only as much power as it takes to light three 100-watt light bulbs. Otherwise, the satellite would overheat. "That's about five times less power per channel than in typical particle-physics experiments," Johnson says. "We'll be pushing our design and engineering in that area. Much of the rest of the technology already exists."

If GLAST succeeds, it will form a perfect partner to MILAGRO, a gamma-ray observatory under construction near Los Alamos National Laboratory in New Mexico. MILAGRO uses the dark waters of a covered reservoir to watch for ghostly flashes of light--the debris from gamma-ray collisions in the atmosphere. UCSC astrophysicists, led by Donald Coyne, are contributing their expertise in electronics and astronomy to the project. GLAST will probe lower-energy gamma rays, while MILAGRO is best for gamma rays produced by the most energetic events in the universe.

Johnson says he spends about one-quarter of his time working on GLAST. He devotes a similar amount of time to the "B factory," an advanced particle-physics machine under development at the Stanford Linear Accelerator Center. About half of his time goes toward teaching and working with undergraduate and graduate students at UCSC.

Editor's note: You may reach Robert Johnson at johnson@scipp.ucsc.edu or (408) 459-2125.

This release is also available on the World Wide Web at UCSC's "Services for Journalists" site (http://www.ucsc.edu/news/journalist.html) or via modem from UC NewsWire (209/244-6971).

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