Electronic Design

Spencer Klein: Mapping The Neutrino Sky

One of the world's next best "telescopes" will not peer out into space. Instead, it will probe deep into the ice of the South Pole for a better picture of the high-energy universe.

The project, dubbed "IceCube," will use 4800 optical sensors sitting 2500 m below the polar surface to detect fundamental particles called neutrinos as they pass through the earth. The goal is to map the "neutrino sky," which will pinpoint sources of high-energy cosmic rays that constantly pelt earth.

Lawrence Berkeley National Laboratory physicist Spencer Klein has been involved in creating and testing the telescope's optical sensors - a "dream job" for this Stanford PhD physicist who has focused part of his career on building instrumentation for high-level physics experiments.

"We know that somewhere in the universe, there are some very high-energy accelerators that produce huge showers of particles," Klein says. "Their cosmic rays are charged, but they don't point back to the source. They do, however, accelerate neutrinos, which will point back to the source."

So far, most neutrinos that have been detected originate from the sun. The only neutrinos that have been tracked to outside the solar system are from a nearby supernova. Yet scientists know that the cosmic rays they've detected point to other sources of high-energy neutrinos.

Part of this "dream job" of helping map the universe's neutrino sources - supernova remnants, gamma ray bursts, and active galactic nuclei (galaxies with black holes at the center) - entailed living at the South Pole for three weeks. There, Klein tested the precision of these optical sensors, which collect data autonomously and send packetized digital information about neutrinos back to the polar surface.

The device's high-tech timing calibration circuits maintain timing accurately to better than 3 ns, Klein said. The challenge is maintaining that accuracy at blisteringly cold temperatures.

"Where else would you worry about finding electronics that will work at minus 50 degrees centigrade?" Klein asks.

These sensors will detect the optical light emitted by other fast-moving electrically-charged particles like electrons that have collided with a highenergy neutrino and penetrated the earth. Upon completion in 2010, IceCube will detect the direction that each neutrino came from and how much energy it carried.

Klein has already been involved in a handful of other astronomy projects, like working on waveform digitizers to observe gamma ray astronomy at Boston University. But it's his current work at the South Pole that's made his a dream career.

"This is very good astronomy," Klein says, "and going to the South Pole has been the experience of a lifetime."

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