Weighing up the superheavies

摘要

Nuclear reactions allow us to create elements beyond uranium (element 92), the heaviest element in nature. However, we are far from knowing what the heaviest possible element is. In the sparsely explored territory of super-heavy elements, an 'island of stability' is expected. This island would consist of isotopes of elements that are more strongly bound and longer-lived than the isotopes surrounding it. Challenging expeditions towards the island have so far led to the discovery of elements up to element 118. But knowing the masses of the isotopes of elements heavier than uranium (trans-uranium elements) is of great importance for the success of the journey. In this issue (page 785), Block and colleagues' describe the first-ever direct measurement of the masses of isotopes of a trans-uranium element. They have used an ion trap as a high-precision scale for weighing isotopes of nobelium, an element that has ten more protons than uranium.rnChemical elements are sorted into a periodic table according to their properties. These properties reflect an atom's electronic structure, which is determined by the number ofrnprotons in the atomic nucleus. In a similar way, the approximately 3,000 known isotopes of the different elements are depicted in a proton number-neutron number diagram, the chart of nuclides. Most of these isotopes are radioactive and can be produced only artificially by using nuclear reactions. In exploring the limits to the existence of nuclides, physicists' expeditions have reached beyond uranium (92 protons) towards the northeast end of the chart of nuclides.