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Direct mass measurements above uranium bridge the gap to the island of stability


The mass of an atom incorporates all its constituents and their interactions1. The difference between the mass of an atom and the sum of its building blocks (the binding energy) is a manifestation of Einstein’s famous relation E = mc2. The binding energy determines the energy available for nuclear reactions and decays (and thus the creation of elements by stellar nucleosynthesis), and holds the key to the fundamental question of how heavy the elements can be. Superheavy elements have been observed in challenging production experiments2,3,4, but our present knowledge of the binding energy of these nuclides is based only on the detection of their decay products. The reconstruction from extended decay chains introduces uncertainties that render the interpretation difficult. Here we report direct mass measurements of trans-uranium nuclides. Located at the farthest tip of the actinide species on the proton number–neutron number diagram, these nuclides represent the gateway to the predicted island of stability. In particular, we have determined the mass values of 252-254No (atomic number 102) with the Penning trap mass spectrometer SHIPTRAP5. The uncertainties are of the order of 10 keV/c2 (representing a relative precision of 0.05 p.p.m.), despite minute production rates of less than one atom per second. Our experiments advance direct mass measurements by ten atomic numbers with no loss in accuracy, and provide reliable anchor points en route to the island of stability.

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Figure 1: Cyclotron resonance curve of 253No2+.
Figure 2: Comparison of the mass values obtained in this work with the results of the latest atomic-mass evaluation.
Figure 3: Part of the chart of nuclides between uranium and element 118.


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We thank D. Lunney for help with the preparation of the manuscript. The project was supported in part by the German Federal Ministry of Education and Research, the Max-Planck Society, and the Helmholtz Association. D.R. acknowledges support from Junta de Andalucia.

Author Contributions M.B. and M.D. performed the data analysis. M.B., K.B. and L.S. prepared the manuscript. All authors helped to perform the experiment, discussed the results, and commented on the manuscript at all stages.

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Block, M., Ackermann, D., Blaum, K. et al. Direct mass measurements above uranium bridge the gap to the island of stability. Nature 463, 785–788 (2010).

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