DOE News
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    The DOE Science News Source is a Newswise initiative to promote research news from the Office of Science of the DOE to the public and news media.
    • 2015-05-28 07:05:00
    • Article ID: 634665

    Protons Hog the Momentum in Neutron-Rich Nuclei

    New research could change our view of neutron stars and other systems with neutron-rich nuclei.

    • Credit: Image courtesy of Jefferson Lab

      Illustration of Jefferson Lab's CEBAF Large Acceptance Spectrometer (CLAS), along with an event reconstructed from the data. In this experiment, an incident 5-GeV electron scatters from a nucleon (a proton or a neutron) that has briefly paired up with another. As particles flying out of the target enter the CLAS, their paths are bent by a magnet and measured by successive layers of different types of particle detectors.

    The Science

    Like dancers swirling on the dance floor with bystanders looking on, protons and neutrons that have briefly paired up inside an atom’s nucleus have a higher-than-average momentum, leaving less energy for non-paired nucleons. This phenomenon allows more protons than neutrons to have high momentum in a relatively neutron-rich nuclei, which is contrary to long-accepted theories. Using data from nuclear physics experiments carried out at the Department of Energy's Thomas Jefferson National Accelerator Facility, researchers have shown – for the first time – that this phenomenon exists in nuclei heavier than carbon, including aluminum, iron, and lead.

    The Impact

    The results of this study show that the Pauli exclusion principle, long used to describe the distribution of protons and neutrons in nuclei, does not accurately describe proton-neutron pairing. These results could change our understanding of the internal structures of systems where these pairings occur, including neutron stars.

    Summary

    In 2008, researchers obtained direct evidence that protons and neutrons in light nuclei (up to carbon, with six each protons and neutrons) pair up briefly in the nucleus, a phenomenon called a short-range correlation. In this pairing, protons preferred neutrons to other protons by 20 to 1. The protons and neutrons involved in a short-range correlation carry higher momentum than unpaired ones. Now, researchers have extended that result into heavier, neutron-rich nuclei, including aluminum (13p/14n), iron (26p/30n), and lead (82p/126n). They found that in these imbalanced nuclei, the minority protons tended to more likely to be found in a short-range correlation than the majority neutrons. The result comes from an initiative in which data from a completed experiment conducted in 2004 were re-analyzed to look for this phenomenon. It was made possible by the CEBAF Large Acceptance Spectrometer (CLAS) that was used to collect the data. The CLAS detectors almost completely surround an experimental target and can collect more than 2 terabytes of data a day. The result can likely be extended to other imbalanced systems, such as the atoms in ultra-cold atomic gases and in the cores of neutron stars.

    Funding

    This work was supported by the U.S. Department of Energy's Office of Science, the U.S. National Science Foundation, Israel Science Foundation, Chilean Comisión Nacional de Investigación Científica y Technológica, French Centre National de la Recherche Scientifique and Commissariat a l'Energie Atomique, French-American Cultural Exchange, Italian Istituto Nazionale di Fisica Nucleare, National Research Foundation of Korea, and the U.K.'s Science and Technology Facilities Council. CEBAF is a DOE Office of Science user facility.

    Publications

    O. Hen, et al., "Momentum sharing in imbalanced Fermi systems." Science 346, 614 (2014). [DOI: 10.1126/science.1256785]

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    The Milky Way's Satellites Help Reveal Link Between Dark Matter Halos and Galaxy Formation

    The Milky Way's Satellites Help Reveal Link Between Dark Matter Halos and Galaxy Formation

    Just like we orbit the sun and the moon orbits us, the Milky Way has satellite galaxies with their own satellites. Drawing from data on those galactic neighbors, a new model suggests the Milky Way should have an additional 100 or so very faint satellite galaxies awaiting discovery.

    Making Biofuels Cheaper by Putting Plants to Work

    Making Biofuels Cheaper by Putting Plants to Work

    One strategy to make biofuels more competitive is to make plants do some of the work themselves. Scientists can engineer plants to produce valuable chemical compounds, or bioproducts, as they grow. Then the bioproducts can be extracted from the plant and the remaining plant material can be converted into fuel. But one important part of this strategy has remained unclear -- exactly how much of a particular bioproduct would plants need to make in order to make the process economically feasible?

    Capturing 3D microstructures in real time

    Capturing 3D microstructures in real time

    Argonne researchers have invented a machine-learning based algorithm for quantitatively characterizing material microstructure in three dimensions and in real time. This algorithm applies to most structural materials of interest to industry.

    A new way to fine-tune exotic materials: Thin, stretch and clamp

    A new way to fine-tune exotic materials: Thin, stretch and clamp

    Turning a brittle oxide into a flexible membrane and stretching it on a tiny apparatus flipped it from a conducting to an insulating state and changed its magnetic properties. The technique can be used to study and design a broad range of materials for use in things like sensors and detectors.

    An innovative model of the dynamic magnetic field that surrounds Mercury

    An innovative model of the dynamic magnetic field that surrounds Mercury

    The first detailed model of the interaction between the solar wind and the magnetic field that surrounds Mercury, findings that could lead to improved understanding of the stronger field around Earth.

    Story Tips: Molding matter atom by atom and seeing inside uranium particles

    Story Tips: Molding matter atom by atom and seeing inside uranium particles

    Story Tips: Molding matter atom by atom and seeing inside uranium particles, from the Department of Energy's Oak Ridge National Laboratory

    Scientists See Energy Gap Modulations in a Cuprate Superconductor

    Scientists See Energy Gap Modulations in a Cuprate Superconductor

    Scientists studying high-Tc superconductors at the U.S. Department of Energy's Brookhaven National Laboratory have definitive evidence for the existence of a state of matter known as a pair density wave--first predicted by theorists some 50 years ago. Their results show that this phase coexists with superconductivity in a well-known bismuth-based copper-oxide superconductor.

    Uncertain Climate Future Could Disrupt Energy Systems

    Uncertain Climate Future Could Disrupt Energy Systems

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    Argonne and CERN weigh in on the origin of heavy elements

    Argonne and CERN weigh in on the origin of heavy elements

    Nuclear physicists from Argonne National Laboratory led an international physics experiment conducted at CERN that utilizes novel techniques developed at Argonne to study the nature and origin of heavy elements in the universe.

    A new explanation for sudden collapses of heat in plasmas can help create fusion energy on Earth

    A new explanation for sudden collapses of heat in plasmas can help create fusion energy on Earth

    PPPL researchers find that jumbled magnetic fields in the core of fusion plasmas can cause the entire plasma discharge to suddenly collapse.


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    Argonne's Paul Dickman honored with nuclear waste management achievement award

    Argonne's Paul Dickman honored with nuclear waste management achievement award

    Paul Dickman has been named a Waste Management Symposium Fellow for 2020.

    Using Fiber Optics to Advance Safe and Renewable Energy

    Using Fiber Optics to Advance Safe and Renewable Energy

    Fiber optic cables, it turns out, can be incredibly useful scientific sensors. Researchers at Lawrence Berkeley National Laboratory have studied them for use in carbon sequestration, groundwater mapping, earthquake detection, and monitoring of Arctic permafrost thaw. Now they have been awarded new grants to develop fiber optics for two novel uses: monitoring offshore wind operations and underground natural gas storage.

    Brookhaven Lab's Lijun Wu Receives 2020 Chuck Fiori Award

    Brookhaven Lab's Lijun Wu Receives 2020 Chuck Fiori Award

    For the past 20 years, Wu has been advancing quantitative electron diffraction to study batteries, catalysts, and other energy materials.

    Jefferson Lab Temporarily Suspends Operations

    Jefferson Lab Temporarily Suspends Operations

    In an effort to minimize the risk to the Jefferson Lab workforce and in keeping with recommendations from national, state, and local authorities, the Department of Energy's Thomas Jefferson National Accelerator Facility is temporarily suspending operations.

    Department of Energy to Provide $60 Million for Science Computing Teams

    The U.S. Department of Energy (DOE) announced a plan to provide $60 million to establish multidisciplinary teams to develop new tools and techniques to harness supercomputers for scientific discovery.

    Fermilab, UNICAMP and Sao Paulo Research Foundation collaborate on major international projects for neutrino research

    Fermilab, UNICAMP and Sao Paulo Research Foundation collaborate on major international projects for neutrino research

    Under a new agreement, the University of Campinas and the Sao Paulo Research Foundation will play important roles in the Long-Baseline Neutrino Facility and the international Deep Underground Neutrino Experiment, hosted by Fermilab.

    New $21.4 million U.S.-Israel center aims to develop water-energy technologies

    New $21.4 million U.S.-Israel center aims to develop water-energy technologies

    A U.S.-Israel team that includes researchers from the U.S. Department of Energy's Argonne National Laboratory has received $21.4 million to develop new technologies to help solve global water challenges.

    Argonne's Valerii Vinokur awarded Fritz London Prize

    Argonne's Valerii Vinokur awarded Fritz London Prize

    Valerii Vinokur, a senior scientist and distinguished fellow at the U.S. Department of Energy's (DOE) Argonne National Laboratory, has been awarded the Fritz London Memorial Prize for his work in condensed matter and theoretical physics.

    Register to Join a Special April 16 Media Tour of a Telescope Instrument that Will Create a 3D Map of Millions of Galaxies

    Register to Join a Special April 16 Media Tour of a Telescope Instrument that Will Create a 3D Map of Millions of Galaxies

    Members of the media are invited to attend a mid-April dedication of the Dark Energy Spectroscopic Instrument (DESI), which is scheduled to begin its five-year mission to construct a 3D map of the universe in the coming months.

    Department of Energy to Provide $100 Million for Solar Fuels Research

    The U.S. Department of Energy (DOE) announced a plan to provide up to $100 million over five years for research on artificial photosynthesis for the production of fuels from sunlight.


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    Harvesting Energy from Light using Bio-inspired Artificial Cells

    Harvesting Energy from Light using Bio-inspired Artificial Cells

    Scientists designed and connected two different artificial cells to each other to produce molecules called ATP (adenosine triphosphate).

    Engineering Living Scaffolds for Building Materials

    Engineering Living Scaffolds for Building Materials

    Bone and mollusk shells are composite systems that combine living cells and inorganic components. This allows them to regenerate and change structure while also being very strong and durable. Borrowing from this amazing complexity, researchers have been exploring a new class of materials called engineered living materials (ELMs).

    Excavating Quantum Information Buried in Noise

    Excavating Quantum Information Buried in Noise

    Researchers developed two new methods to assess and remove error in how scientists measure quantum systems. By reducing quantum "noise" - uncertainty inherent to quantum processes - these new methods improve accuracy and precision.

    How Electrons Move in a Catastrophe

    How Electrons Move in a Catastrophe

    Lanthanum strontium manganite (LSMO) is a widely applicable material, from magnetic tunnel junctions to solid oxide fuel cells. However, when it gets thin, its behavior changes for the worse. The reason why was not known. Now, using two theoretical methods, a team determined what happens.

    When Ions and Molecules Cluster

    When Ions and Molecules Cluster

    How an ion behaves when isolated within an analytical instrument can differ from how it behaves in the environment. Now, Xue-Bin Wang at Pacific Northwest National Laboratory devised a way to bring ions and molecules together in clusters to better discover their properties and predict their behavior.

    Tune in to Tetrahedral Superstructures

    Tune in to Tetrahedral Superstructures

    Shape affects how the particles fit together and, in turn, the resulting material. For the first time, a team observed the self-assembly of nanoparticles with tetrahedral shapes.

    Tracing Interstellar Dust Back to the Solar System's Formation

    Tracing Interstellar Dust Back to the Solar System's Formation

    This study is the first to confirm dust particles pre-dating the formation of our solar system. Further study of these materials will enable a deeper understanding of the processes that formed and have since altered them.

    Investigating Materials that Can Go the Distance in Fusion Reactors

    Investigating Materials that Can Go the Distance in Fusion Reactors

    Future fusion reactors will require materials that can withstand extreme operating conditions, including being bombarded by high-energy neutrons at high temperatures. Scientists recently irradiated titanium diboride (TiB2) in the High Flux Isotope Reactor (HFIR) to better understand the effects of fusion neutrons on performance.

    Better 3-D Imaging of Tumors in the Breast with Less Radiation

    Better 3-D Imaging of Tumors in the Breast with Less Radiation

    In breast cancer screening, an imaging technique based on nuclear medicine is currently being used as a successful secondary screening tool alongside mammography to improve the accuracy of the diagnosis. Now, a team is hoping to improve this imaging technique.

    Microbes are Metabolic Specialists

    Microbes are Metabolic Specialists

    Scientists can use genetic information to measure if microbes in the environment can perform specific ecological roles. Researchers recently analyzed the genomes of over 6,000 microbial species.


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