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In this issue:
Unique SSRL–Stanford Collaboration Illuminates Rare Materials
Science Today: Cosmological Results from Observations of Galaxy Clusters
Photo of the Day: SAFE07 Recognition
SLAC's Klystron Legacy

SLAC Today

Thursday - January 24, 2008

Unique SSRL–Stanford Collaboration Illuminates
Rare Materials

SSRL Researcher Rob Moore at beamline 5-4's Angle Resolved Photoemission Spectroscope (ARPES). (Click on image for larger version. Photo credit
Brad Plummer.)

Take two high-tech X-ray beam lines, a table-top apparatus, half a dozen researchers and a material made with one of the rarest elements on earth. Combine them in a collaborative venture to bring to light the best, first clear picture of the material's properties.

That is the heart of recent work done at the Geballe Laboratory for Advanced Materials at Stanford University and at beam lines 5-4 and 7-2 at the Stanford Synchrotron Radiation Laboratory (SSRL). Such a synergistic effort is an example of how to solve one puzzle by applying the power of multiple researchers and approaches.

Combining their resources and techniques, the researchers examined little-studied compounds made of tellurium—a semi-metal that is one of the rarest elements on earth—and one of the "rare earth" elements, which actually aren't so rare. Read more...

(Daily Column - Science Today)

Cosmological Results from Observations of Galaxy Clusters


A cosmological simulation of structure formation. (Image courtesy of the Virgo Consortium.)

In addition to the well-understood radiation and baryonic matter, our universe contains weakly interacting dark matter and dark energy. Very little is known about the latter two, despite the fact that they constitute about 95% of the total mass of the universe. Understanding the nature of these dark components is central both to cosmology and to fundamental physics.

Clusters of galaxies are the largest dynamically equilibrated structures in the universe, and are among the most luminous persistent sources in the sky. As such, they provide an essential laboratory for understanding cosmology. In collaboration with professor Steve Allen, postdoctoral researcher David Rapetti and professor Harald Ebeling (University of Hawaii), I have been studying the growth of cosmic structure by observing the evolution of the X-ray luminosity function of massive clusters. Since most of the baryonic content of such objects consists of hot gas, these clusters can be effectively identified through all-sky, X-ray flux limited surveys. X-ray observables such as luminosity and temperature also correlate well with cluster masses, allowing the survey observations to be statistically related the mass function, the number of objects in the universe as a function of mass and time. This work has produced new constraints on the mean density of dark matter, the amplitude of density fluctuations and the dark energy equation of state that are consistent with those of independent cosmological tests. The growth of structure measurement is complementary to other leading cosmological observations, and in combination with other current data promises to significantly improve our knowledge. In the future, this work will benefit from an influx of new data, particularly through our collaboration with others in the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) who are studying clusters using the complementary method of gravitational lensing.

Photo of the Day: SAFE07 Recognition

(Photo - SAFE07)
Image courtesy of Diana Rogers. (Click on image for larger version.)

Persis Drell, Department of Energy Site Office Manager Paul Golan and members of the Directorate gathered in the Panofsky Auditorium Lobby on Tuesday morning to honor those featured in the SAFE07 campaign.

"I want to thank you all for being a part of this," Drell told the participants. "This campaign is so wonderful because it recognizes what people have done right."

"We already have fewer accidents this year than we did at this point last year," said Golan. "I hope that each and every one of you can help continue this trend by sharing successful safety practices with your coworkers. Safety is not an accident—it relies on good people looking after each other."

SLAC's Klystron Legacy

(Photo - Klystron display)
SLAC's klystron display, located in the lobby of Building 44. (Click image for larger version.)

On January 30, 1939, the Palo Alto Times published the headline, "New Stanford Invention Heralds Revolutionary Changes." Sixty-nine years have passed and "revolutionary" still encapsulates the klystron's legacy. A museum-worthy display in Building 44's Klystron & Microwave Department chronicles the device's history through photographs, descriptions and genuine pieces of the technology.

A klystron is an electron tube that converts electricity into microwaves for applications as diverse as radar, cancer treatment, broadcast television transmission and, of course, particle acceleration.

"The klystron is the radio frequency [RF] source of choice anywhere you need very high peak power and narrow bandwidth," engineer Glenn Scheitrum said. "Nothing will touch the klystron for the peak RF power levels needed in storage rings and accelerators." Read more...

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