Physics—Elements at extremes

Physics—Elements at extremes

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Dawn Levy, Communications
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 Steven Pain/Oak Ridge National Laboratory, U.S. Dept. of Energy Position-sensitive silicon detectors form the “nerves” of the Super Oak Ridge Rutgers University Barrel Array and yield high spatial resolution that enabled the Sn-132 experiment at ORNL—the first neutron-removal reaction on such a heavy, neutron-rich nucleus. The array is now installed at Michigan State University for later use at the Facility for Rare Isotope Beams, anticipated to begin operations in 2022. Credit: Steven Pain/Oak Ridge National Laboratory, U.S. Dept. of Energy (hi-res image)
November 1, 2018 — In neutron star mergers and supernovae, lighter elements absorb neutrons to create heavier elements whose nuclei are neutron-rich and radioactive. To better understand this phenomenon, physicists turned to the “doubly magic” tin isotope Sn-132, colliding it with a target at Oak Ridge National Laboratory to assess its properties as it lost a neutron to become Sn-131. The results, published after years of complex data analysis, were combined with a prior experiment in which a nucleus of Sn-132 gained a neutron to become Sn-133. “Many ambiguities are reduced by systematically studying the addition and subtraction of neutrons,” said ORNL’s Steven Pain. “This is the first time this technique has been applied to such a heavy neutron-rich nucleus. These results will help benchmark theoretical models and guide future investigations of unstable nuclei with even greater neutron surpluses.” The experiment was the last conducted at ORNL’s Holifield Radioactive Ion Beam Facility before it ceased operations in 2012.  

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