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In this issue:
Listening for Whispers of Dark Matter
Profile: Patrick Krejcik
AIS: Bolometers and the Big Bang

SLAC Today

Wednesday - January 10, 2007

Listening for Whispers of Dark Matter

(Image - bells)
Hitting an atom inside a crystal, a dark matter particle would cause vibrations, similar to the ringing of a bell. CDMS scientists can distinguish this "sound" from the vibrations caused by other particles traversing the crystal, such as neutrons and cosmic rays. (Image courtesy of Sandbox Studio.)

Jodi Cooley works half a mile underground, in a mine that stopped operating 40 years ago. A rattling elevator takes her to work, 27 floors beneath the surface. The ride down the mineshaft is five minutes of complete darkness. A colony of bats inhabits the mine.

"For someone who's squeamish," says Cooley, "it's not the best work environment." When she is on shift she spends 10 hours a day in the mine, 10 days in a row. Looking to find a new type of particle, Cooley is listening for whispers of dark matter.

The underground experiment she works on, a collaboration of 60 physicists and engineers, is the world's most sensitive search for a type of particle that, as of yet, has only been theorized. The Cryogenic Dark Matter Search (CDMS) uses detectors chilled nearly to the lowest possible temperature, minus 273 degrees Celsius, to "listen" for vibrations caused by these particles streaming in from space. The discovery of these particles would revolutionize our view of the cosmos.  Read more...

(Weekly Column - Profile)

Patrick Krejcik:
Diving with Sharks

(Image - Patrick Krejcik)
Patrick Krejcik, who works on LCLS, dives near Thailand's Similan Islands in December, 2006. He pauses at his safety stop to take a photo, allowing his body to purge itself of some absorbed nitrogen. (Click on image for larger version.)

Patrick Krejcik, a native of Sydney, grew up swimming and surfing along Australia's coasts. Last year, he returned to his oceanic roots when he traveled to Thailand to learn to scuba dive.

"We spent four days and four nights on a live-aboard boat cruising Thailand's Andaman Sea," Krejcik said. "Basically, all we did was eat, sleep, and dive."

With rigorous training, he was able to swim to depths of 120 feet below the water's surface—sixty feet deeper than the permissible depth for most beginners.

"I wasn't worried," he said, "The training was very thorough."

To stay safe, divers need to avoid harmful nitrogen buildups. Krejcik breathed oxygen-enriched Nitrox, which contains less nitrogen than air. He ascended slowly to avoid the decompression sickness a buildup can cause.

Krejcik explained, "It's like opening a soda bottle slowly to release the pressure gradually and prevent micro bubbles forming in the bloodstream." Before resurfacing, he paused at his "safety stop" fifteen feet below the water's surface to adjust to pressure changes.

AIS: Bolometers
and the Big Bang

SLAC's newest seminar series, the Advanced Instrumentation Seminars (AIS), kicks off today with a presentation by visiting speaker Helmuth Spieler. A physicist at Lawrence Berkeley National Laboratory (LBNL), Spieler will discuss instrumentation for future studies of the Cosmic Microwave Background (CMB), the remnant radiation left over from the Big Bang.

The AIS series aims to foster information sharing and cross-disciplinary collaboration in instrumentation research and development. Spieler is a fitting presenter for the first AIS talk, as he launched LBNL's Interdisciplinary Instrumentation Colloquium two years ago and has been organizing it ever since. He says researchers and developers can benefit greatly from the exchange of ideas and expertise through forums such as AIS. "What strikes me again and again is how often we are unaware of what's going on next door," he says.

Spieler's presentation will focus on the development of large-scale superconducting bolometer arrays and their readout for the next generation of CMB experiments. The talk will review physics goals, measurement techniques, bolometers for both temperature anisotropy and polarization measurements, and a novel readout scheme with a discussion of some key technical details.

All are invited to attend Spieler's presentation, which will take place at 1:30 p.m. in the 3rd floor conference room of the Kavli Building. For additional information, visit the AIS website.

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