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Physical Chemistry

Heavy Element Gets Weighed

Ion-trap mass spec technique allows direct weighing of nobelium isotopes, a first for a transuranium element

by Elizabeth K. Wilson
February 15, 2010 | A version of this story appeared in Volume 88, Issue 7

With an ingenious ion-trap device, researchers have directly weighed the mass of several isotopes of nobelium—the first such measurements of an element heavier than uranium (Nature 2010, 463, 785). Until now, the masses of very heavy elements could only be inferred from the masses of their radioactive decay products. An international team led by Michael Block of the Institute for Heavy-Ion Research (GSI), in Darmstadt, Germany, recorded the masses of 252No, 253No, and 254No, which have half-lives on the order of seconds. The researchers used an ion-trap mass spectrometer that receives and weighs single atoms as soon as they’re produced. The mass of a nucleus includes not only protons and neutrons but also the binding energies that hold them together, the researchers point out. Without direct mass measurements, calculated binding energies can be quite uncertain and make it difficult to explore the nuclear behavior of transuranium elements. Thus, the new method could aid the study of elements approaching the “island of stability,” an uncharted region of the periodic table around 120 protons and 184 neutrons where elements are expected to have half-lives of minutes or even hours.


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