Scientists Discover 1st 'Neutron-Rich' Isotope of Uranium Since 1979

An anonymous reader quotes a report from Live Science: Scientists have discovered and synthesized an entirely new isotope of the highly radioactive element uranium. But it might last only 40 minutes before decaying into other elements. The new isotope, uranium-241, has 92 protons (as all uranium isotopes do) and 149 neutrons, making it the first new neutron-rich isotope of uranium discovered since 1979. While atoms of a given element always have the same number of protons, different isotopes, or versions, of those elements may hold different numbers of neutrons in their nuclei. To be considered neutron-rich, an isotope must contain more neutrons than is common to that element. "We measured the masses of 19 different actinide isotopes with a high precision of one part per million level, including the discovery and identification of the new uranium isotope," Toshitaka Niwase(opens in new tab), a researcher at the High-energy Accelerator Research Organization (KEK) Wako Nuclear Science Center (WNSC) in Japan, told Live Science in an email. "This is the first new discovery of a uranium isotope on the neutron-rich side in over 40 years." Niwase is the lead author of a study on the new uranium isotope, which was published March 31 in the journal Physical Review Letters. Niwase and colleagues created the uranium-241 by firing a sample of uranium-238 at platinum-198 nuclei at Japan's RIKEN accelerator. The two isotopes then swapped neutrons and protons - a phenomenon called "multinucleon transfer." The team then measured the mass of the created isotopes by observing the time it took the resulting nuclei to travel a certain distance through a medium. The experiment also generated 18 new isotopes, all of which contained between 143 and 150 neutrons.

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