1. GSI Helmholtzzentrum für Schwerionenforschung GmbH, Planckstrasse 1, 64291 Darmstadt, Germany


2. Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany


3. Ernst-Moritz-Arndt-Universität Greifswald, Felix-Hausdorff-Str. 6, 17489 Greifswald, Germany


4. Justus-Liebig-Universität Gießen, Heinrich-Buff-Ring 16, 35390 Gießen, Germany


5. Johannes Gutenberg-Universität, Staudingerweg 7, 55128 Mainz, Germany


6. Ruprecht-Karls-Universität, Philosophenweg 12, 69120 Heidelberg, Germany


7. Dipartimento di Fisica and INFN Sezione di Padova, Via Marzolo 8, 35131 Padova, Italy


8. PNPI RAS, Gatchina, Leningrad district 188300, Russia


9. Flerov Laboratory of Nuclear Reactions, JINR 141980 Dubna, Russia


10. University of Jyväskylä, PO Box 35 (YFL), 40014 Jyväskylä, Finland


11. Departamento de FAMN, Universidad de Granada, 18071 Granada, Spain


12. Ludwig-Maximilians-Universität München, Am Coulombwall 1, 85748 Garching, Germany


13. Present addresses: Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA (S.R.); Ludwig-Maximilians-Universität München, Am Coulombwall 1, 85748 Garching, Germany (C.W.).

Correspondence to: M. Block¹ Correspondence and requests for materials should be addressed to M.B. (Email: m.block@gsi.de).

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 = mc ². 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 experiments^{2, 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/c ² (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.