David Kirkpatrick

November 18, 2008

Billions of anti-matter particles

Very interesting research.

The release:

Billions of particles of anti-matter
created in laboratory

LIVERMORE, Calif. – Take a gold sample the size of the head of a push pin, shoot a laser through it, and suddenly more than 100 billion particles of anti-matter appear.

The anti-matter, also known as positrons, shoots out of the target in a cone-shaped plasma “jet.”

This new ability to create a large number of positrons in a small laboratory opens the door to several fresh avenues of anti-matter research, including an understanding of the physics underlying various astrophysical phenomena such as black holes and gamma ray bursts.

Anti-matter research also could reveal why more matter than anti-matter survived the Big Bang at the start of the universe.

“We’ve detected far more anti-matter than anyone else has ever measured in a laser experiment,” said Hui Chen, a Livermore researcher who led the experiment. “We’ve demonstrated the creation of a significant number of positrons using a short-pulse laser.”

Chen and her colleagues used a short, ultra-intense laser to irradiate a millimeter-thick gold target. “Previously, we concentrated on making positrons using paper-thin targets,” said Scott Wilks, who designed and modeled the experiment using computer codes. “But recent simulations showed that millimeter-thick gold would produce far more positrons. We were very excited to see so many of them.”

In the experiment, the laser ionizes and accelerates electrons, which are driven right through the gold target. On their way, the electrons interact with the gold nuclei, which serve as a catalyst to create positrons. The electrons give off packets of pure energy, which decays into matter and anti-matter, following the predictions by Einstein’s famous equation that relates matter and energy. By concentrating the energy in space and time, the laser produces positrons more rapidly and in greater density than ever before in the laboratory.

“By creating this much anti-matter, we can study in more detail whether anti-matter really is just like matter, and perhaps gain more clues as to why the universe we see has more matter than anti-matter,” said Peter Beiersdorfer, a lead Livermore physicist working with Chen.

Particles of anti-matter are almost immediately annihilated by contact with normal matter, and converted to pure energy (gamma rays). There is considerable speculation as to why the observable universe is apparently almost entirely matter, whether other places are almost entirely anti-matter, and what might be possible if anti-matter could be harnessed. Normal matter and anti-matter are thought to have been in balance in the very early universe, but due to an “asymmetry” the anti-matter decayed or was annihilated, and today very little anti-matter is seen.

Over the years, physicists have theorized about anti-matter, but it wasn’t confirmed to exist experimentally until 1932. High-energy cosmic rays impacting Earth’s atmosphere produce minute quantities of anti-matter in the resulting jets, and physicists have learned to produce modest amounts of anti-matter using traditional particle accelerators. Anti-matter similarly may be produced in regions like the center of the Milky Way and other galaxies, where very energetic celestial events occur. The presence of the resulting anti-matter is detectable by the gamma rays produced when positrons are destroyed when they come into contact with nearby matter.

Laser production of anti-matter isn’t entirely new either. Livermore researchers detected anti-matter about 10 years ago in experiments on the since-decommissioned Nova “petawatt” laser – about 100 particles. But with a better target and a more sensitive detector, this year’s experiments directly detected more than 1 million particles. From that sample, the scientists infer that around 100 billion positron particles were produced in total.

Until they annihilate, positrons (anti-electrons) behave much like electrons (just with an opposite charge), and that’s how Chen and her colleagues detected them. They took a normal electron detector (a spectrometer) and equipped it to detect particles with opposite polarity as well.

“We’ve entered a new era,” Beiersdorfer said. “Now, that we’ve looked for it, it’s almost like it hit us right on the head. We envision a center for antimatter research, using lasers as cheaper anti-matter factories.”

Chen will present her work at the American Physical Society’s Division of Plasma Physics meeting Nov. 17-21 at the Hyatt Regency Reunion in Dallas. S.C. Wilks, E. Liang, J. Myatt, K. Cone ,L. Elberson, D.D. Meyerhofer, M. Schneider, R. Shepherd, D. Stafford, R. Tommasini, P. Beiersdorfer are the collaborators on this project.

Founded in 1952, Lawrence Livermore National Laboratory is a national security laboratory, with a mission to ensure national security and apply science and technology to the important issues of our time. Lawrence Livermore National Laboratory is managed by Lawrence Livermore National Security, LLC for the U.S. Department of Energy’s National Nuclear Security Administration.

November 14, 2008

First images of new multi-planet solar system

The release:

Astronomers capture first images of
newly-discovered solar system

LIVERMORE, Calif. — Astronomers for the first time have taken snapshots of a multi-planet solar system, much like ours, orbiting another star.

The new solar system orbits a dusty young star named HR8799, which is 140 light years away and about 1.5 times the size of our sun. Three planets, roughly 10, 10 and 7 times the mass of Jupiter, orbit the star. The size of the planets decreases with distance from the parent star, much like the giant planets do in our system.

And there may be more planets out there, but scientists say they just haven’t seen them yet.

“Every extrasolar planet detected so far has been a wobble on a graph. These are the first pictures of an entire system,” said Bruce Macintosh, an astrophysicist from Lawrence Livermore National Laboratory and one of the key authors of a paper appearing in the Nov. 13 issue of Science Express.We’ve been trying image planets for eight years with no luck and now we have pictures of three planets at once.”

Using high-contrast, near-infrared adaptive optics observations with the Keck and Gemini telescopes, the team of researchers from Livermore, the NRC Herzberg Institute of Astrophysics in Canada, Lowell Observatory, University of California Los Angeles, and several other institutions were able to see three orbiting planetary companions to HR8799.

Astronomers have known for a decade through indirect techniques that the sun was not the only star with orbiting planets.

“But we finally have an actual image of an entire system,” Macintosh said. “This is a milestone in the search and characterization of planetary systems around stars.”

During the past 10 years, various planet detection techniques have been used to find more than 200 exoplanets. But these methods all have limitations. Most infer the existence of a planet through its influence on the star that it orbits, but don’t actually tell scientists anything about the planet other than its mass and orbit. Second, the techniques are all limited to small to moderate planet-star separation, usually less than about 5 astronomical units (one AU is the average distance from the sun to Earth).

In the new findings, the planets are 24, 37 and 67 times the Earth-sun separation from the host star. The furthest planet in the new system orbits just inside a disk of dusty debris, similar to that produced by the comets of the Kuiper belt of our solar system (just beyond the orbit of Neptune at 30 times Earth-sun distance).

“HR8799’s dust disk stands out as one of the most massive in orbit around any star within 300 light years of Earth” said UCLA’s Ben Zuckerman.

In some ways, this planetary system seems to be a scaled-up version of our solar system orbiting a larger and brighter star, Macintosch said.

The host star is known as a bright, blue A-type star. These types of stars are usually ignored in ground and space-based direct imaging surveys since they offer a less favorable contrast between a bright star and a faint planet. But they do have an advantage over our sun: Early in their life, they can retain heavy disks of planet-making material and therefore form more massive planets at wider separations that are easier to detect. In the recent study, the star also is young – less than 100 million years old – which means its planets are still glowing with heat from their formation.

“Seeing these planets directly – separating their light from the star – lets us study them as individuals, and use spectroscopy to study their properties, like temperature or composition,” Macintosh said.

“Detailed comparison with theoretical model atmospheres confirms that all three planets possess complex atmospheres with dusty clouds partially trapping and re-radiating the escaping heat” said Lowell Observatory astronomer Travis Barman.

The planets have been extensively studied using adaptive optics on the giant Keck and Gemini telescopes on Mauna Kea, Hawaii. Adaptive optics enables astronomers to minimize the blurring effects of the Earth’s atmosphere, producing images with unprecedented detail and resolution. LLNL helped build the original adaptive optics system for Keck, the world’s largest optical telescope. Christian Marois, a former LLNL postdoctoral researcher and the primary author of the paper who now works at NRC, developed an advanced computer processing technique that helps to extract the planets from the vastly brighter light of the star.

A team led by Macintosh is constructing a much more advanced adaptive optics system designed from the beginning to block the light of bright stars and reveal even fainter planets. Known as the Gemini Planet Imager (http://gpi.berkeley.edu), this new system will be up to 100 times more sensitive than current instruments and able to image planets similar to our own Jupiter around nearby stars.

“I think there’s a very high probability that there are more planets in the system that we can’t detect yet,” Macintosh said. “One of the things that distinguishes this system from most of the extrasolar planets that are already known is that HR8799 has its giant planets in the outer parts – like our solar system does – and so has ‘room’ for smaller terrestrial planets – far beyond our current ability to see – in the inner parts.”

Founded in 1952, Lawrence Livermore National Laboratory is a national security laboratory, with a mission to ensure national security and apply science and technology to the important issues of our time. Lawrence Livermore National Laboratory is managed by Lawrence Livermore National Security, LLC for the U.S. Department of Energy’s National Nuclear Security Administration.

Near-infrared false-color image taken with the W.M. Keck II telescope and adaptive optics. The three planets are labelled b, c, and d. The colored speckles in the center are the remains of the bright light from their parent star after image processing.

Near-infrared false-color image taken with the W.M. Keck II telescope and adaptive optics. The three planets are labelled b, c, and d. The colored speckles in the center are the remains of the bright light from their parent star after image processing.

August 2, 2008

Looking inside aerogels

Aerogels are pretty amazing substances with many uses. This press release covers using X-ray diffraction to get a 3D nanoscale look inside aerogels.

The full release and two of the provided images:

X-Ray Diffraction Looks Inside Aerogels in 3-D

A multi-institutional team of scientists has used beamline 9.0.1 at the Advanced Light Source to perform high-resolution x‑ray diffraction imaging of an aerogel for the first time, revealing its nanoscale three-dimensional bulk lattice structure down to features measured in nanometers, billionths of a meter.

Aerogels, sometimes called “frozen smoke” or “San Francisco fog,” are nanoscale foams: solid materials whose sponge-like structure is riddled by pores as small as nanometers across and whose strength is surprising, given their low density. Many porous materials are extraordinary for their properties as insulators, filters, and catalysts; they are used to produce clean fuels, to insulate windows and even clothing, to study the percolation of oil through rock, as drug-delivery systems, and even to cushion the capture of high-velocity comet fragments in outer space.

“The smallest pore size is the key to the strength of porous materials and what they can do,” says Stefano Marchesini, an ALS scientist at Berkeley Lab, who led the research. “Seeing inside bulk porous materials has never been done before at this resolution, making this one of the first applications of x-ray diffractive microscopy to a real problem.” 

Team members from Lawrence Livermore National Laboratory, the University of California at Davis, Arizona State University, Argonne National Laboratory, and Berkeley Lab performed the x‑ray diffraction imaging and have published their results online in Physical Review Letters, available to subscribers at http://link.aps.org/abstract/PRL/v101/e055501.

Seeing inside foam

One way to study aerogels and other nanofoams is with electron microscopy, which can image only thin, two-dimensional slices through the porous structure of the material. Another method is straightforward x-ray microscopy, using zone plates as “lenses”; microscopy can penetrate a sample but has difficulty maintaining resolution at different depths in the material. Small-angle x‑ray scattering (SAXS) can also gather limited structural information from finely powdered aerogels, but SAXS cannot provide full three-dimensional information. None of these techniques can capture the 3-D internal structure of nanofoam samples measured in micrometers, a few millionths of a meter across.

X-ray diffraction approaches the problem differently. A laser-like x-ray beam passes all the way through the sample and is diffracted onto a CCD detector screen; diffraction patterns are repeatedly stored while the sample is moved and rotated. A typical series requires approximately 150 views in all.

The individual diffraction patterns are then processed by a computer. The way the photons in the beam are redirected from each component of the structure is different for each orientation, and comparing their intensities serves to position that component precisely in three-dimensional space. Thousands of iterations are required – in the present study, team member Anton Barty of Livermore led the solution of almost 100 million measured intensities, as opposed to the 100 thousand or so typical of, say, protein crystallography – but the end result is a 3‑D image of the tiny sample at nanometer-scale resolution.

Foam-like structures are described in terms of interconnecting lattice beams and the nodes where they intersect. These elements became vividly apparent in the reconstructed 3-D images of the aerogel used in the imaging at the ALS, which was made of tantalum ethoxide (Ta2O5), a ceramic material proposed for cladding capsules of hydrogen isotopes for inertial-confinement fusion experiments being pursued at Livermore.

“The strength and stiffness of foam-like structures are expected to scale with their density, relating the density of individual elements like beams and nodes to the overall density,” Marchesini says. “But below about 10 percent density, the strength of aerogels like the ones we tested – on the order of 1 percent density – is orders of magnitude less than expected.”

Of the theories that seek to explain this phenomenon, one is the “percolation” model, in which fragments become detached from the load-bearing structure and add mass without contributing to strength. The alternate “heterogeneities” model proposes that the structure is increasingly riddled with defects like micron-sized holes and buckles more easily.

A third theory is the “diffusion-limited cluster aggregation” model: blobs of material accumulate that are connected by thin links, instead of sturdy beams between nodes.

“The high resolution we achieved allowed us to see which of these models more accurately described the actual observed structure,” Marchesini says. By seeing the foam from the inside, the team was able to see exactly how it was structured, and the shape and dimensions of each component. “The structure was far more complex than anything we’d seen in earlier images obtained using this technique.”

What the team observed in their 3-D images of the tantalum ethoxide aerogel was a “blob-and-beam” structure consistent with the third model, that of diffusion-limited cluster aggregation. The observed structure explained the relative weakness of the low-density material and also suggested that changes in methods of preparing aerogels might improve their strength.

Into the future

“We’d like to use x-ray diffraction to study a range of porous materials and nanostructures in general, for example porous polymers developed at the Molecular Foundry for storing hydrogen as fuel – and at even higher resolutions,” Marchesini says. “To do so, David Shapiro, who built the end station we used for this work, is working with us to overcome some obstacles.”

One is time. At present, each sample takes months of work. After preparation, the experiment first requires one or two days of mounting, rotating, and exposing the sample to the x-ray beam, about a minute per view – because of a slow detector – for 150 views. There follow weeks of computation time. “And after all this, you can find out the sample was no good, so you have to start over,” Marchesini says.

Improved sample handling, faster detectors, and a beamline dedicated to x-ray diffraction are principal goals. The Coherent Scattering and Diffraction Microscopy (COSMIC) facility, a top priority in the ALS strategic plan, will provide intense coherent x-rays with full polarization control.

“We are also collaborating with Berkeley Lab’s Computational Research Division to develop efficient and robust algorithms to speed up the time needed to construct the 3-D image from the individual rotated views,” Marchesini says. “This will open an entire spectrum of possibilities for new ways of seeing the very small – not just aerogels but virtually any unknown object, from nanostructures to biological cells.”

This work was principally supported by the Department of Energy through a variety of grants, by Laboratory Directed Research and Development programs at Livermore, and additionally by the National Science Foundation.

Additional information

  • “Three-dimensional coherent X-ray diffraction imaging of a ceramic nanofoam: determination of structural deformation mechanisms,” by A. Barty, S. Marchesini, H. N. Chapman, C. Cui, M. R. Howells, D. A. Shapiro, A. M. Minor, J. C. H. Spence, U. Weierstall, J. Havsky, A. Noy, S. P. Hau-Riege, A. B. Artyukhin, T. Baumann, T. Willey, J. Stolken, T. van Buuren, and J. H. Kinney, appears in Physical Review Letters online publication and is available to subscribers at http://link.aps.org/abstract/PRL/v101/e055501.
  • More about beamline 9.0.1 at the Advanced Light Source
Silicon aerogel acting as an insulator

Silicon aerogel acting as an insulator

 

A 500-nanometer cube of aerogel from the interior of the 3-D volume, reconstructed by x-ray diffraction. The foam structure shows globular nodes that are interconnected by thin beam- like struts. Approximately 85 percent of the total mass is associated with the nodes; relatively little of the mass is in the load-bearing links.
A 500-nanometer cube of aerogel from the interior of the 3-D volume, reconstructed by x-ray diffraction. The foam structure shows globular nodes that are interconnected by thin beam- like struts. Approximately 85 percent of the total mass is associated with the nodes; relatively little of the mass is in the load-bearing links.

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