MIT Research News' Journal
 
[Most Recent Entries] [Calendar View]

Friday, July 24th, 2020

    Time Event
    9:52a
    Commentary: America must invest in its ability to innovate

    In July of 1945, in an America just beginning to establish a postwar identity, former MIT vice president Vannevar Bush set forth a vision that guided the country to decades of scientific dominance and economic prosperity. Bush’s report to the president of the United States, “Science: The Endless Frontier,” called on the government to support basic research in university labs. Its ideas, including the creation of the National Science Foundation (NSF), are credited with helping to make U.S. scientific and technological innovation the envy of the world.

    Today, America’s lead in science and technology is being challenged as never before, write MIT President L. Rafael Reif and Indiana University President Michael A. McRobbie in an op-ed published today by The Chicago Tribune. They describe a “triple challenge” of bolder foreign competitors, faster technological change, and a merciless race to get from lab to market.

    The government’s decision to adopt Bush’s ideas was bold and controversial at the time, and similarly bold action is needed now, they write.

    “The U.S. has the fundamental building blocks for success, including many of the world’s top research universities that are at the forefront of the fight against COVID-19,” reads the op-ed. “But without a major, sustained funding commitment, a focus on key technologies and a faster system for transforming discoveries into new businesses, products and quality jobs, in today’s arena, America will not prevail.”

    McRobbie and Reif believe a bipartisan bill recently introduced in both chambers of Congress can help America’s innovation ecosystem meet the challenges of the day. Named the “Endless Frontier Act,” the bill would support research focused on advancing key technologies like artificial intelligence and quantum computing. It does not seek to alter or replace the NSF, but to “create new strength in parallel,” they write. 

    The bill would also create scholarships, fellowships, and other forms of assistance to help build an American workforce ready to develop and deploy the latest technologies. And, it would facilitate experiments to help commercialize new ideas more quickly.

    “Today’s leaders have the opportunity to display the far-sighted vision their predecessors showed after World War II — to expand and shape of our institutions, and to make the investments to adapt to a changing world,” Reif and McRobbie write.

    Both university presidents acknowledge that measures such as the Endless Frontier Act require audacious choices. But if leaders take the right steps now, they write, those choices will seem, in retrospect, obvious and wise.

    “Now as then, our national prosperity hinges on the next generation of technical triumphs,” Reif and Mcrobbie write. “Now as then, that success is not inevitable, and it will not come by chance. But with focused funding and imaginative policy, we believe it remains in reach.”

    2:00p
    An origin story for a family of oddball meteorites

    Most meteorites that have landed on Earth are fragments of planetesimals, the very earliest protoplanetary bodies in the solar system. Scientists have thought that these primordial bodies either completely melted early in their history or remained as piles of unmelted rubble.

    But a family of meteorites has befuddled researchers since its discovery in the 1960s. The diverse fragments, found all over the world, seem to have broken off from the same primordial body, and yet the makeup of these meteorites indicates that their parent must have been a puzzling chimera that was both melted and unmelted.

    Now researchers at MIT and elsewhere have determined that the parent body of these rare meteorites was indeed a multilayered, differentiated object that likely had a liquid metallic core. This core was substantial enough to generate a magnetic field that may have been as strong as Earth’s magnetic field is today.

    Their results, published today in the journal Science Advances, suggest that the diversity of the earliest objects in the solar system may have been more complex than scientists had assumed.

    “This is one example of a planetesimal that must have had melted and unmelted layers. It encourages searches for more evidence of composite planetary structures,” says lead author Clara Maurel, a graduate student in MIT’s Department of Earth, Atmospheric, and Planetary Sciences (EAPS). “Understanding the full spectrum of structures, from nonmelted to fully melted, is key to deciphering how planetesimals formed in the early solar system.”

    Maurel’s co-authors include EAPS Professor Benjamin Weiss, along with collaborators at Oxford University, Cambridge University, the University of Chicago, Lawrence Berkeley National Laboratory, and the Southwest Research Institute.

    Oddball irons

    The solar system formed around 4.5 billion years ago as a swirl of super-hot gas and dust. As this disk gradually cooled, bits of matter collided and merged to form progressively larger bodies, such as planetesimals.

    The majority of meteorites that have fallen to Earth have compositions that suggest they came from such early planetesimals that were either of two types: melted, and unmelted. Both types of objects, scientists believe, would have formed relatively quickly, in less than a few million years, early in the solar system’s evolution.

    If a planetesimal formed in the first 1.5 million years of the solar system, short-lived radiogenic elements could have melted the body entirely due to the heat released by their decay. Unmelted planetesimals could have formed later, when their material had lower quantities of radiogenic elements, insufficient for melting.

    There has been little evidence in the meteorite record of intermediate objects with both melted and unmelted compositions, except for a rare family of meteorites called IIE irons.

    “These IIE irons are oddball meteorites,” Weiss says. “They show both evidence of being from primordial objects that never melted, and also evidence for coming from a body that’s completely or at least substantially melted. We haven’t known where to put them, and that’s what made us zero in on them.”

    Magnetic pockets

    Scientists have previously found that both melted and unmelted IIE meteorites originated from the same ancient planetesimal, which likely had a solid crust overlying a liquid mantle, like Earth. Maurel and her colleagues wondered whether the planetesimal also may have harbored a metallic, melted core.

    “Did this object melt enough that material sank to the center and formed a metallic core like that of the Earth?” Maurel says. “That was the missing piece to the story of these meteorites.”

    The team reasoned that if the planetesimal did host a metallic core, it could very well have generated a magnetic field, similar to the way Earth’s churning liquid core produces a magnetic field. Such an ancient field could have caused minerals in the planetesimal to point in the direction of the field, like a needle in a compass. Certain minerals could have kept this alignment over billions of years.

    Maurel and her colleagues wondered whether they might find such minerals in samples of IIE meteorites that had crashed to Earth. They obtained two meteorites, which they analyzed for a type of iron-nickel mineral known for its exceptional magnetism-recording properties.

    The team analyzed the samples using the Lawrence Berkeley National Laboratory’s

    Advanced Light Source, which produces X-rays that interact with mineral grains at the nanometer scale, in a way that can reveal the minerals’ magnetic direction.

    Sure enough, the electrons within a number of grains were aligned in a similar direction — evidence that the parent body generated a magnetic field, possibly up to several tens of microtesla, which is about the strength of Earth’s magnetic field. After ruling out less plausible sources, the team concluded that the magnetic field was most likely produced by a liquid metallic core. To generate such a field, they estimate the core must have been at least several tens of kilometers wide.

    Such complex planetesimals with mixed composition (both melted, in the form of a liquid core and mantle, and unmelted in the form of a solid crust), Maurel says, would likely have taken over several million years to form — a formation period that is longer than what scientists had assumed until recently.

    But where within the parent body did the meteorites come from? If the magnetic field was generated by the parent body’s core, this would mean that the fragments that ultimately fell to Earth could not have come from the core itself. That’s because a liquid core only generates a magnetic field while still churning and hot. Any minerals that would have recorded the ancient field must have done so outside the core, before the core itself completely cooled.

    Working with collaborators at the University of Chicago, the team ran high-velocity simulations of various formation scenarios for these meteorites. They showed that it was possible for a body with a liquid core to collide with another object, and for that impact to dislodge material from the core. That material would then migrate to pockets close to the surface where the meteorites originated.

    “As the body cools, the meteorites in these pockets will imprint this magnetic field in their minerals. At some point, the magnetic field will decay, but the imprint will remain,” Maurel says. “Later on, this body is going to undergo a lot of other collisions until the ultimate collisions that will place these meteorites on Earth’s trajectory.”  

    Was such a complex planetesimal an outlier in the early solar system, or one of many such differentiated objects? The answer, Weiss says, may lie in the asteroid belt, a region populated with primordial remnants.

    “Most bodies in the asteroid belt appear unmelted on their surface,” Weiss says. “If we’re eventually able to see inside asteroids, we might test this idea. Maybe some asteroids are melted inside, and bodies like this planetesimal are actually common.”

    This research was funded, in part, by NASA.

    3:25p
    Novel gas-capture approach advances nuclear fuel management

    Nuclear energy provides about 20 percent of the U.S. electricity supply, and over half of its carbon-free generating capacity.   

    Operations of commercial nuclear reactors produce small quantities of spent fuel, which in some countries is reprocessed to extract materials that can be recycled as fuel in other reactors. Key to the improvement of the economics of this fuel cycle is the capture of gaseous radioactive products of fission such as 85krypton.

    Therefore, developing efficient technology to capture and secure 85krypton from the mix of effluent gasses would represent a significant improvement in the management of used nuclear fuels. One promising avenue is the adsorption of gasses into an advanced type of soft crystalline material, metal organic frameworks (MOFs), which have extremely high porosity and enormous internal surface area and can incorporate a vast array of organic and inorganic components.

    Recently published research by a multidisciplinary group that includes members of MIT’s Department of Nuclear Science and Engineering (NSE) represents one of the first steps toward practical application of MOFs for nuclear fuel management, with novel findings on efficacy and radiation resistance, and an initial concept for implementation.

    One fundamental challenge is that the mix of gasses produced during fuel reprocessing is rich in oxygen and nitrogen, and existing methods tend to collect them as well as the part-per-million quantities of krypton that represent the highest risk. This reduces the purity of the collected 85Kr and increases the waste volume. Moreover, existing krypton extraction methods rely on costly and complex cryogenic processes.

    The group’s study, published in the journal Nature Communications, evaluated a series of ultra-microporous MOFs with different metal centers including zinc, cobalt, nickel, and iron, and found that a copper-containing crystal, SIFSIX-Cu, showed good promise.

    To harness its favorable combination of radiation stability and selective adsorption, while also minimizing the volume of waste, the team proposed a two-step treatment process, in which an initial bed of the material is used to adsorb xenon and carbon dioxide from the effluent gas mixture, after which the gas is transferred to a second bed which selectively adsorbs krypton but not nitrogen or oxygen.

    “If one day we want to treat the spent fuels, which in the U.S. are currently stored in pools and dry casks at the nuclear power plant sites, we need to handle the volatile radionuclides.” explains Ju Li, MIT’s Battelle Energy Alliance Professor of Nuclear Science and Engineering and professor of materials science and engineering. “Physisorption of krypton and xenon is a good approach, and we were very happy to collaborate with this large team on the MOF approach.”

    MOFs have been seen as a possible solution for applications in many fields, but this research marks the first systematic study of their applicability in the nuclear sector, and the effectiveness of different metal centers on MOF radiation stability, notes Sameh K. Elsaidi, a research scientist at the U.S. Department of Energy’s National Energy and Technology Laboratory and the paper’s lead author.

    “There are already over 60,000 different MOFs, and more are being developed every day, so there are a lot to choose from,” says Elsaidi. “The selection of one for 85Kr separation during reprocessing is based on several essential criteria. During our long search for porous materials that can meet these criteria, we found that a class of microporous MOFs called SIFSIX-3-M can efficiently reduce the volume of nuclear waste by separating 85Kr in more pure form from the other nonradioactive gasses. However, in order to be useful for practical separation of 85Kr, these materials must be resistant to radiation under reprocessing conditions.

    “This is a first look at candidates that can meet the criteria. I feel very lucky to be working with Ju and [MIT NSE postdoc Ahmed Sami Helal] as we start to evaluate whether these materials can be used in the real world. This project was a very good example of how collaborative work can lead to better fundamental understanding, and there’s a lot down the road that we can do together,” adds Elsaidi.

    Helal notes, “Studying the effect of high-energy ionizing radiation, including β-rays and γ-rays, on the stability of MOFs is a very important factor in determining whether the MOFs can be used for capture of fission gasses from used fuel. This work is the first to investigate the radiolytic stability of MOFs at radiation doses relevant to practical Xe/Kr separation at fuel reprocessing plants.”

    Developing a practical adsorption process is a complex task, requiring capabilities from multiple disciplines including chemical engineering, materials science, and nuclear engineering. The research leveraged several specialized Institute resources, including the MIT gamma irradiation facility (managed by the MIT Radiation Protection Program) and the High Voltage Research Laboratory, which was used for beta irradiation measurements with assistance from Mitchell Galanek of the MIT Office of Environment, Health and Safety.

    Those efforts, in conjunction with X-ray diffraction studies and electronic structure modeling, “were fascinating and helped us learn a lot about MOFs and build our understanding of non-neutronic radiation resistance of this new class of materials,” says Li. “That could be useful in other applications in the future,” including detectors.

    In addition to MIT and the National Energy Technology Laboratory, collaborators on the project included the Pacific Northwest National Laboratory (Praveen Thallapally), the University of Pittsburgh (Mona Mohamed), and the University of South Florida (Brian Space and Tony Pham). Programmatic funding was provided by the U.S. Department of Energy’s Office of Nuclear Energy, with additional support from the National Science Foundation. Computational resources were made available via an XSEDE Grant and by the University of South Florida.

    << Previous Day 2020/07/24
    [Calendar]
    Next Day >>

MIT Research News   About LJ.Rossia.org