Techniques for the discovery of new elements

Abstract

Search for new elements is part of the broader field of investigations of nuclei at the limits of stability. In two series of experiments at SHIP, six new elements ( Z = 107–112) were synthesized via fusion reactions by 1n-deexcitation channels using lead or bismuth targets. The isotopes were unambiguously identified by means of αα correlations. Alpha decay, and not fission, is the dominant decay mode due to strong shell effects. Cross sections drop by two orders of magnitude from nielsbohrium ( Z = 107) to element 112, for which a cross section of 1 pb was measured. The development of intensive beam currents and sensitive detection methods is a necessity, aiming at production and identification of still heavier elements and new isotopes of already known elements, as well as small α-, β- and fission-branching ratios. An equally sensitive set-up is needed for measurement of excitation functions at low cross sections. Our results give hope that isotopes of element 114 close to the island of spherical superheavy elements could be produced by fusion reactions using 208Pb or 209Bi targets. Systematic studies of the reaction cross sections indicate that transfer of nucleons is the important process to initiate the fusion process.