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  • richardmitnick 2:14 pm on November 22, 2014 Permalink | Reply
    Tags: , Carbon studies,   

    Johns Hopkins University: “Deep-Earth Carbon Offers Clues About Origin of Life on Earth” 

    Johns Hopkins
    Johns Hopkins University

    Nov. 20, 2014
    Jill Rosen
    Office: 443-997-9906
    Cell: 443-547-8805
    jrosen@jhu.edu

    A Johns Hopkins-led team links new organic carbon species in deep fluids to the formation of diamonds — and life itself.

    New findings by a Johns Hopkins University-led team reveal long unknown details about carbon deep beneath the Earth’s surface and suggest ways this subterranean carbon might have influenced the history of life on the planet.

    The team also developed a new, related theory about how diamonds form in the Earth’s mantle.

    For decades scientists had little understanding of how carbon behaved deep below the Earth’s surface even as they learned more and more about the element’s vital role at the planet’s crust. Using a model created by Johns Hopkins geochemist Dimitri Sverjensky, Sverjensky, Vincenzo Stagno of the Carnegie Institution of Washington and Fang Huang, a Johns Hopkins graduate student, became the first to calculate how much carbon and what types of carbon exist in fluids at 100 miles below the Earth’s surface at temperatures up to 2,100 degrees F.

    ds
    Dimitri Sverjensky

    In an article published this week in the journal Nature Geoscience, Sverjensky and his team demonstrate that in addition to the carbon dioxide and methane already documented deep in subduction zones, there exists a rich variety of organic carbon species that could spark the formation of diamonds and perhaps even become food for microbial life.

    “It is a very exciting possibility that these deep fluids might transport building blocks for life into the shallow Earth,” said Sverjensky, a professor in the Department of Earth and Planetary Sciences. “This may be a key to the origin of life itself.”

    Sverjensky’s theoretical model, called the Deep Earth Water model, allowed the team to determine the chemical makeup of fluids in the Earth’s mantle, expelled from descending tectonic plates. Some of the fluids, those in equilibrium with mantle peridotite minerals, contained the expected carbon dioxide and methane. But others, those in equilibrium with diamonds and eclogitic minerals, contained dissolved organic carbon species including a vinegar-like acetic acid.

    These high concentrations of dissolved carbon species, previously unknown at great depth in the Earth, suggest they are helping to ferry large amounts of carbon from the subduction zone into the overlying mantle wedge where they are likely to alter the mantle and affect the cycling of elements back into the Earth’s atmosphere.

    The team also suggested that these mantle fluids with dissolved organic carbon species could be creating diamonds in a previously unknown way. Scientists have long believed diamond formation resulted through chemical reactions starting with either carbon dioxide or methane. The organic species offer a range of different starting materials, and an entirely new take on the creation of the gemstones.

    The research is part of a 10-year global project to further understanding of carbon on Earth called the Deep Carbon Observatory. The work is funded by the Alfred P. Sloan Foundation.

    See the full article here.

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    The Johns Hopkins University opened in 1876, with the inauguration of its first president, Daniel Coit Gilman. “What are we aiming at?” Gilman asked in his installation address. “The encouragement of research … and the advancement of individual scholars, who by their excellence will advance the sciences they pursue, and the society where they dwell.”

    The mission laid out by Gilman remains the university’s mission today, summed up in a simple but powerful restatement of Gilman’s own words: “Knowledge for the world.”

    What Gilman created was a research university, dedicated to advancing both students’ knowledge and the state of human knowledge through research and scholarship. Gilman believed that teaching and research are interdependent, that success in one depends on success in the other. A modern university, he believed, must do both well. The realization of Gilman’s philosophy at Johns Hopkins, and at other institutions that later attracted Johns Hopkins-trained scholars, revolutionized higher education in America, leading to the research university system as it exists today.

     
  • richardmitnick 4:27 pm on November 17, 2014 Permalink | Reply
    Tags: , Carbon studies, , ,   

    From LBL: “As Temperatures Rise, Soil Will Relinquish Less Carbon to the Atmosphere Than Currently Predicted” 

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    Berkeley Lab

    November 17, 2014
    Dan Krotz 510-486-4019

    New Berkeley Lab model quantifies interactions between soil microbes and their surroundings

    Here’s another reason to pay close attention to microbes: Current climate models probably overestimate the amount of carbon that will be released from soil into the atmosphere as global temperatures rise, according to research from the US Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab).

    The findings are from a new computer model that explores the feedbacks between soil carbon and climate change. It’s the first such model to include several physiologically realistic representations of how soil microbes break down organic matter, a process that annually unleashes about ten times as much carbon into the atmosphere as fossil fuel emissions. In contrast, today’s models include a simplistic representation of microbial behavior.

    The research is published Nov. 17 on the website of the journal Nature Climate Change.

    Based on their results, the Berkeley Lab scientists recommend that future Earth system models include a more nuanced and dynamic depiction of how soil microbes go about the business of degrading organic matter and freeing up carbon.

    This approach could help scientists more accurately predict what will happen to soil carbon as Earth’s climate changes. These predictions are especially important in vulnerable regions like the Arctic, which is expected to warm considerably this century, and which holds a vast amount of carbon in the tundra.

    “We know that microbes are the agents of change when it comes to decomposing organic matter. But the question is: How important is it to explicitly quantify complex microbial interactions in climate models?” says Jinyun Tang, a scientist in Berkeley Lab’s Earth Sciences Division who conducted the research with fellow Berkeley Lab scientist William Riley.

    “We found that it makes a big difference,” Tang says. ”We showed that warming temperatures would return less soil carbon to the atmosphere than current models predict.”

    mod
    The complex and dynamic livelihood of soil microbes is captured in this schematic. For the first time, these processes are represented in a computer model that predicts the fate of soil carbon as temperatures rise. (Credit: Berkeley Lab)

    Terrestrial ecosystems, such as the Arctic tundra and Amazon rainforest, contain a huge amount of carbon in organic matter such as decaying plant material. Thanks to soil microbes that break down organic matter, these ecosystems also contribute a huge amount of carbon to the atmosphere.

    al
    The soil above the Arctic Circle near Barrow, Alaska contains a tremendous amount of carbon. New research may help scientists better predict how much of this carbon will be released as the climate warms.

    Because soil is such a major player in the carbon cycle, even a small change in the amount of carbon it releases can have a big affect on atmospheric carbon concentrations. This dynamic implies that climate models should represent soil-carbon processes as accurately as possible.

    But here’s the problem: Numerous empirical experiments have shown that the ways in which soil microbes decompose organic matter, and respond to changes in temperature, vary over time and from place to place. This variability is not captured in today’s ecosystem models, however. Microbes are depicted statically. They respond instantaneously when they’re perturbed, and then revert back as if nothing happened.

    To better portray the variability of the microbial world, Tang and Riley developed a numerical model that quantifies the costs incurred by microbes to respire, grow, and consume energy. Their model accounts for internal physiology, such as the production of enzymes that help microbes break down organic matter. It includes external processes, such as the competition for these enzymes once they’re outside the microbe. Some enzymes adsorb onto mineral surfaces, which means they are not available to chew through organic matter. The model also includes competition between different microbial populations.

    Together, these interactions—from enzymes to minerals to populations­—represent microbial networks as ever-changing systems, much like what’s observed in experiments.

    The result? When the model was subjected to a 4 degrees Celsius change, it predicted more variable but weaker soil-carbon and climate feedbacks than current approaches.

    “There’s less carbon flux to the atmosphere in response to warming,” says Riley. “Our representation is more complex, which has benefits in that it’s likely more accurate. But it also has costs, in that the parameters used in the model need to be further studied and quantified.”

    Tang and Riley recommend more research be conducted on these microbial and mineral interactions. They also recommend that these features ultimately be included in next-generation Earth system models, such as the Department of Energy’s Accelerated Climate Modeling for Energy, or ACME.

    The research was supported by the Department of Energy’s Office of Science.

    See the full article here.

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  • richardmitnick 1:30 pm on September 4, 2014 Permalink | Reply
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    From PNNL: “Birth of a mineral” 


    PNNL Lab

    September 04, 2014
    Mary Beckman, PNNL, (509) 375-3688

    One of the most important molecules on earth, calcium carbonate crystallizes into chalk, shells and minerals the world over. In a study led by the Department of Energy’s Pacific Northwest National Laboratory, researchers used a powerful microscope that allows them to see the birth of crystals in real time, giving them a peek at how different calcium carbonate crystals form, they report September 5 in Science.

    The results might help scientists understand how to lock carbon dioxide out of the atmosphere as well as how to better reconstruct ancient climates.

    “Carbonates are most important for what they represent, interactions between biology and Earth,” said lead researcher James De Yoreo, a materials scientist at PNNL. “For a decade, we’ve been studying the formation pathways of carbonates using high-powered microscopes, but we hadn’t had the tools to watch the crystals form in real time. Now we know the pathways are far more complicated than envisioned in the models established in the twentieth century.”

    Earth’s Reserve

    Calcium carbonate is the largest reservoir of carbon on the planet. It is found in rocks the world over, shells of both land- and water-dwelling creatures, and pearls, coral, marble and limestone. When carbon resides within calcium carbonate, it is not hanging out in the atmosphere as carbon dioxide, warming the world. Understanding how calcium carbonate turns into various minerals could help scientists control its formation to keep carbon dioxide from getting into the atmosphere.

    Calcium carbonate deposits also contain a record of Earth’s history. Researchers reconstructing ancient climates delve into the mineral for a record of temperature and atmospheric composition, environmental conditions and the state of the ocean at the time those minerals formed. A better understanding of its formation pathways will likely provide insights into those events.

    To get a handle on mineral formation, researchers at PNNL, the University of California, Berkeley, and Lawrence Berkeley National Laboratory [LBNL] examined the earliest step to becoming a mineral, called nucleation. In nucleation, molecules assemble into a tiny crystal that then grows with great speed. Nucleation has been difficult to study because it happens suddenly and unpredictably, so the scientists needed a microscope that could watch the process in real time.

    Come to Order

    In the 20th century, researchers established a theory that crystals formed in an orderly fashion. Once the ordered nucleus formed, more molecules added to the crystal, growing the mineral but not changing its structure. Recently, however, scientists have wondered if the process might be more complicated, with other things contributing to mineral formation. For example, in previous experiments they’ve seen forms of calcium carbonate that appear to be dense liquids that could be sources for minerals.

    Researchers have also wondered if calcite forms from less stable varieties or directly from calcium and carbonate dissolved in the liquid. Aragonite and vaterite are calcium carbonate minerals with slightly different crystal architectures than calcite and could represent a step in calcite’s formation. The fourth form called amorphous calcium carbonate — or ACC, which could be liquid or solid, might also be a reservoir for sprouting minerals.

    To find out, the team created a miniature lab under a transmission electron microscope at the Molecular Foundry, a DOE Office of Science User Facility at LBNL. In this miniature lab, they mixed sodium bicarbonate (used to make club soda) and calcium chloride (similar to table salt) in water. At high enough concentrations, crystals grew. Videos of nucleating and growing crystals recorded what happened:

    tem
    transmission electron microscope at LBNL

    Morphing Minerals

    The videos revealed that mineral growth took many pathways. Some crystals formed through a two-step process. For example, droplet-like particles of ACC formed, then crystals of aragonite or vaterite appeared on the surface of the droplets. As the new crystals formed, they consumed the calcium carbonate within the drop on which they nucleated.

    Other crystals formed directly from the solution, appearing by themselves far away from any ACC particles. Multiple forms often nucleated in a single experiment — at least one calcite crystal formed on top of an aragonite crystal while vaterite crystals grew nearby.

    What the team didn’t see in and among the many options, however, was calcite forming from ACC even though researchers widely expect it to happen. Whether that means it never does, De Yoreo can’t say for certain. But after looking at hundreds of nucleation events, he said it is a very unlikely event.

    “This is the first time we have directly visualized the formation process,” said De Yoreo. “We observed many pathways happening simultaneously. And they happened randomly. We were never able to predict what was going to come up next. In order to control the process, we’d need to introduce some kind of template that can direct which crystal forms and where.”

    In future work, De Yoreo and colleagues plan to investigate how living organisms control the nucleation process to build their shells and pearls. Biological organisms keep a store of mineral components in their cells and have evolved ways to make nucleation happen when and where needed. The team is curious to know how they use cellular molecules to achieve this control.

    This work was supported by the Department of Energy Office of Science.

    See the full article here.

    Pacific Northwest National Laboratory (PNNL) is one of the United States Department of Energy National Laboratories, managed by the Department of Energy’s Office of Science. The main campus of the laboratory is in Richland, Washington.

    PNNL scientists conduct basic and applied research and development to strengthen U.S. scientific foundations for fundamental research and innovation; prevent and counter acts of terrorism through applied research in information analysis, cyber security, and the nonproliferation of weapons of mass destruction; increase the U.S. energy capacity and reduce dependence on imported oil; and reduce the effects of human activity on the environment. PNNL has been operated by Battelle Memorial Institute since 1965.

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  • richardmitnick 5:50 pm on August 11, 2014 Permalink | Reply
    Tags: , Carbon studies,   

    From NASA/JPL at Caltech: “NASA Carbon Counter Reaches Final Orbit, Returns Data” 

    JPL

    August 11, 2014
    Alan Buis
    Jet Propulsion Laboratory, Pasadena, California
    818-354-0474
    alan.buis@jpl.nasa.gov

    Steve Cole
    NASA Headquarters, Washington
    202-358-0918
    stephen.e.cole@nasa.gov

    Just over a month after launch, the Orbiting Carbon Observatory-2 (OCO-2) — NASA’s first spacecraft dedicated to studying atmospheric carbon dioxide — has maneuvered into its final operating orbit and produced its first science data, confirming the health of its science instrument.

    NASA OCO satellite
    NASA OCO

    Atmospheric carbon dioxide is the leading human-produced greenhouse gas responsible for warming our world. It is a critical natural component of Earth’s carbon cycle. OCO-2 will produce the most detailed picture to date of sources of carbon dioxide, as well as their natural “sinks” — places on Earth’s surface where carbon dioxide is removed from the atmosphere. The observatory will study how these sources and sinks are distributed around the globe and how they change over time.

    Following launch from California’s Vandenberg Air Force Base on July 2, OCO-2 underwent a series of steps to configure the observatory for in-flight operations. Mission controllers established two-way communications with the observatory, stabilized its orientation in space and deployed its solar arrays to provide electrical power. The OCO-2 team then performed a checkout of OCO-2′s systems to ensure they were functioning properly.

    Through the month of July, a series of propulsive burns was executed to maneuver the observatory into its final 438-mile (705-kilometer), near-polar orbit at the head of the international Afternoon Constellation, or “A-Train,” of Earth-observing satellites. It arrived there on Aug. 3. Operations are now being conducted with the observatory in an orbit that crosses the equator at 1:36 p.m. local time.

    The A-Train, the first multi-satellite, formation-flying “super observatory” to record the health of Earth’s atmosphere and surface environment, collects an unprecedented quantity of nearly simultaneous climate and weather measurements. OCO-2 is now followed by the Japanese GCOM-W1 satellite, and then by NASA’s Aqua, CALIPSO, CloudSat and Aura spacecraft, respectively — all of which fly over the same point on Earth within 16 minutes of each other.

    With OCO-2 in its final orbit, mission controllers began cooling the observatory’s three-spectrometer instrument to its operating temperatures. The spectrometer’s optical components must be cooled to near 21 degrees Fahrenheit (minus 6 degrees Celsius) to bring them into focus and limit the amount of heat they radiate. The instrument’s detectors must be even cooler, near minus 243 degrees Fahrenheit (minus 153 degrees Celsius), to maximize their sensitivity.

    With the instrument’s optical system and detectors near their stable operating temperatures, the OCO-2 team collected “first light” test data on Aug. 6 as the observatory flew over central Papua New Guinea. The data were transmitted from OCO-2 to a ground station in Alaska, then to NASA’s Goddard Space Flight Center in Greenbelt, Maryland, for initial decoding, and then to NASA’s Jet Propulsion Laboratory in Pasadena, California, for further processing. The test provided the OCO-2 team with its first opportunity to see whether the instrument had reached orbit with the same performance it had demonstrated before launch.

    As OCO-2 flies over Earth’s sunlit hemisphere, each spectrometer collects a “frame” three times each second, for a total of about 9,000 frames from each orbit. Each frame is divided into eight spectra, or chemical signatures, that record the amount of molecular oxygen or carbon dioxide over adjacent ground footprints. Each footprint is about 1.3 miles (2.25 kilometers) long and a few hundred yards (meters) wide. When displayed as an image, the eight spectra appear like bar codes — bright bands of light broken by sharp dark lines. The dark lines indicate absorption by molecular oxygen or carbon dioxide.

    “The initial data from OCO-2 appear exactly as expected — the spectral lines are well resolved, sharp and deep,” said OCO-2 chief architect and calibration lead Randy Pollock of JPL. “We still have a lot of work to do to go from having a working instrument to having a well-calibrated and scientifically useful instrument, but this was an important milestone on this journey.”

    Over the next several weeks, the OCO-2 team will conduct a series of calibration activities to characterize fully the performance of the instrument and observatory. In parallel, OCO-2 will routinely record and return up to 1 million science observations each day. These data will be used initially to test the ground processing system and verify its products. The team will begin delivering calibrated OCO-2 spectra data to NASA’s Goddard Earth Sciences Data and Information Services Center for distribution to the global science community and other interested parties before the end of the year. The team will also deliver estimates of carbon dioxide to that same center for distribution in early 2015.

    OCO-2 is a NASA Earth System Science Pathfinder Program mission managed by JPL for NASA’s Science Mission Directorate in Washington. Orbital Sciences Corporation in Dulles, Virginia, built the spacecraft bus and provides mission operations under JPL’s leadership. The science instrument was built by JPL, based on the instrument design co-developed for the original OCO mission by Hamilton Sundstrand in Pomona, California. NASA’s Launch Services Program at NASA’s Kennedy Space Center in Florida was responsible for launch management.

    NASA monitors Earth’s vital signs from land, air and space with a fleet of satellites and ambitious airborne and ground-based observation campaigns. NASA develops new ways to observe and study Earth’s interconnected natural systems with long-term data records and computer analysis tools to better see how our planet is changing. The agency shares this unique knowledge with the global community and works with institutions in the United States and around the world that contribute to understanding and protecting our home planet.

    See the full article here.

    Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. Although the facility has a Pasadena postal address, it is actually headquartered in the city of La Cañada Flintridge [1], on the northwest border of Pasadena. JPL is managed by the nearby California Institute of Technology (Caltech) for the National Aeronautics and Space Administration. The Laboratory’s primary function is the construction and operation of robotic planetary spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASA’s Deep Space Network.

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  • richardmitnick 9:32 am on August 7, 2014 Permalink | Reply
    Tags: , Carbon studies, ,   

    From physicsworld.com: “Molecular seeds sprout identical carbon nanotubes” 

    physicsworld
    physicsworld.com

    Aug 7, 2014
    Hamish Johnston

    The first effective technique for growing a batch of single-walled carbon nanotubes (SWCNTs) that all have the same molecular structure has been developed by scientists in Switzerland. The new process involves using “seed molecules” on a platinum substrate to grow SWCNTs with the desired structure. The breakthrough could be extremely important to those developing electronic devices based on SWCNTs because nanotubes with different structures can have very different electronic properties.

    tube
    Up, up and away: growing a nanotube from a seed molecule

    An SWCNT can be thought of as an atomically thin sheet of carbon that has been rolled up to form a tube about 1 nm thick, resembling a drinking straw. The carbon sheet always has the same honeycomb structure, which it shares with graphene. However, there are about a hundred different ways that the edges of the sheet can join together to make a tube, and this defines whether an SWCNT conducts electricity like a metal or a semiconductor. In the case of semiconducting nanotubes, the size of the electronic band gap also depends on how the edges are joined.

    Electronic devices based on SWCNTs could, in principle, be used to create transistors and other components that are smaller, faster and more energy efficient than those based on silicon. But before that can happen, scientists have to come up with reliable ways of producing batches of SWCNTs with identical structures.
    Costly separation

    Careful control of how SWCNTs are prepared can limit the number of different structures to as few as five. Then SWCNTs with the desired structure can be separated from a mixture. However, this is a very costly process with a structurally pure sample of SWCNTs costing about $1000 per milligram from a chemical supplier. As a result, scientists are very keen on developing methods for producing batches containing just one structure.

    This latest work was done by Juan Ramon Sanchez-Valencia and colleagues at the Swiss Federal Laboratories for Material Sciences and Technology (Empa) in Zürich.

    grow
    Grown from seed

    The new technique is based on the fact that, unlike a drinking straw, the tips of SWCNTs are capped by carbon atoms and each species has a cap with a different structure. The team used the established technique of organic chemical synthesis to create cap molecules with the same structure as the cap of the desired structural species of SWCNT. These cap molecules are placed on a platinum surface, which is heated in the presence of a carbon-rich gas such as ethylene. The platinum surface acts as a catalyst, pulling carbon atoms from the gas and passing them to the cap molecules. This steady supply of carbon molecules attaches itself to the bottom of a cap and pushes it up from surface, creating an SWCNT with the desired structure.

    Metallic armchairs

    The cap molecules were designed to seed SWCNTs with the “(6,6) armchair” structure. This much-studied type of nanotube is of interest to device designers because it conducts electricity like a metal. The SWCNTs were grown to several hundred nanometres in length before they were analysed using scanning tunnelling microscopy (STM) and Raman spectroscopy. This revealed that the SWCNTS were all of the same type and were free of structural defects.

    “The clever thing about this is that they predesign the cap and that cap then defines the nanotube type,” explains SWCNT expert James Tour at Rice University in the US, who was not involved in the research. Although the team did not show that the technique can create other types of SWCNTs by using different cap molecules, Tour says that this possibility “seems to be implied and it is likely that that would be the case”.

    Making tonnes of nanotubes

    An important benefit of the new technique is that 1 kg of seed molecules could, in principle, produce 5 tonnes of SWCNTs, each 10 μm in length. On the downside, a platinum surface measuring about 30 km2 would be needed to grow such a quantity of SWCNTs.

    An additional challenge facing anyone wanting to use the technique to produce commercial quantities of SWCNTs is how to deal with the entanglement of neighbouring nanotubes. This occurs before the SWCNTs reach a usable length, and disentangling nanotubes can be a tricky process.

    The new technique is described in Nature.

    See the full article here.

    PhysicsWorld is a publication of the Institute of Physics. The Institute of Physics is a leading scientific society. We are a charitable organisation with a worldwide membership of more than 50,000, working together to advance physics education, research and application.

    We engage with policymakers and the general public to develop awareness and understanding of the value of physics and, through IOP Publishing, we are world leaders in professional scientific communications.
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  • richardmitnick 12:57 pm on July 9, 2014 Permalink | Reply
    Tags: , Carbon studies, ,   

    From physicsworld.com: “Carbon nucleus seen spinning in triangular state” 

    physicsworld
    physicsworld.com

    Jul 8, 2014
    Hamish Johnston

    Physicists have obtained important new evidence showing that the structure of the carbon-12 nucleus – without which there would be no life here on Earth – resembles that of an equilateral triangle. The evidence was obtained by physicists in the UK, Mexico and the US by measuring a new rapidly spinning rotational state of the nucleus. The finding suggests that the “Hoyle state” of carbon-12, which plays an important role in the creation of carbon in red giant stars, has the same shape too. Recent theoretical predictions, in contrast, had suggested that the Hoyle state is more like an obtuse triangle or “bent arm”.

    All the carbon in the universe is created in red giant stars by two alpha particles (helium-4 nuclei) fusing to create a short-lived beryllium-8 nucleus, which then captures a third alpha particle to form carbon-12. But exactly how this reaction occurs initially puzzled physicists, whose early understanding of carbon-12 suggested that it would proceed much too slowly to account for the known abundance of carbon in the universe. Then in 1954 the British astronomer Fred Hoyle predicted that carbon-12 had a hitherto unknown excited state – now dubbed the Hoyle state – which boosts the rate of carbon-12 production.

    Three years later the Hoyle state was confirmed experimentally by physicists working at Caltech. However, the precise arrangement of the protons and neutrons in the carbon-12 nucleus remains a matter of much debate. While some physicists feel that carbon-12 is best thought of as 12 interacting nucleons, others believe that the nucleus can be modelled as three alpha particles that are bound together. The rational for the latter model is that alpha particles are extremely stable and so are likely to endure within the carbon-12 nucleus.
    Molecular inspiration

    If carbon-12 is indeed well described as three alpha particles, molecular physics could provide important clues about how those particles are arranged. In 2000 Roelof Bijker of the National Autonomous University of Mexico (UNAM) and Francesco Iachello at Yale University suggested that the three alpha particles could arrange themselves in an equilateral triangle in which the three alpha particles are all in the same plane. Such a structure had already been spotted five years earlier in the triatomic hydrogen molecular ion, H3+.

    Now, Bijker has joined forces with Martin Freer and colleagues at the University of Birmingham and Moshe Gai at the University of Connecticut to obtain the best experimental evidence so far that carbon-12 is indeed shaped like an equilateral triangle. The experiment was carried out at Birmingham’s cyclotron by firing a beam of alpha particles at a carbon target to produce carbon-12 nuclei that are in high spin states. Indeed, the nuclei, which literally spin like tops, are rotating so fast that they tear apart by emitting alpha particles.

    man
    The University of Birmingham’s cyclotron

    By measuring the energy and angular distribution of the alpha particles, the team observed a high spin state that had never been seen before. When analysed along with four lower spin states measured in previous experiments, the new data suggest very strongly that the carbon-12 nucleus resembles an equilateral triangle that has been set spinning like a three-pointed pinwheel.

    Breathing nucleus

    This description applies to the ground-state rotational band of carbon-12, but it also has significance for the Hoyle state. This is because the spectrum of the Hoyle-state rotational band appears to be similar to that of the ground-state band – with two of the five spin states measured already. However, the Hoyle state appears to have a larger moment of inertia than the ground state. This suggests that the Hoyle state is a “breathing mode” whereby the equilateral triangle expands. This expanded nucleus can itself be set spinning, resulting in a series of excited states similar to that of the ground-state band of carbon-12.

    This evidence pointing towards an equilateral-triangle-shaped Hoyle state appears to be at odds with the recent calculations that suggested that it is more like an obtuse triangle. However, alpha-decay measurements do not give physicists the complete picture of the shape of a nucleus and the only way to be sure of the structure is to study the gamma rays that are given off when a spin state decays. While such studies are commonplace in nuclear physics, they are much harder for carbon-12 because the nucleus is much more likely to decay by emitting an alpha particle than a gamma ray.

    Freer and colleagues are now, however, developing an experiment that will try to capture the gamma rays given off by the spinning carbon-12 nuclei and hope to be making measurements before the end of this year. So 60 years after the Hoyle state was predicted, we may finally know its shape.

    The research is described in Physical Review Letters.

    See the full article here.

    PhysicsWorld is a publication of the Institute of Physics. The Institute of Physics is a leading scientific society. We are a charitable organisation with a worldwide membership of more than 50,000, working together to advance physics education, research and application.

    We engage with policymakers and the general public to develop awareness and understanding of the value of physics and, through IOP Publishing, we are world leaders in professional scientific communications.
    IOP Institute of Physics


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