19. Production and Identification of Transactinide Elements

Microscopic nuclear theories predict a region of superheavy elements (SHEs) at the next doubly magic shell closure above ²⁰⁸Pb. Early models locate the shell closure at Z = 114, more recent calculations place it at Z = 120. The closed neutron shell is located at N = 184. These predictions motivated the search for superheavy elements in nature and in the laboratory to explore the limits of the chart of nuclides toward its upper end. A new region of shell stabilization, centered at Z = 108 and N = 162 has been discovered. It interconnects the transuranium region and the superheavy elements. As of 2009, the heaviest element accepted by the Union of Pure and Applied Chemistry is Z = 112. The discovery of elements 113 to 116 and 118 has been reported. All of these elements have been created by the complete fusion of heavy ions. Production rates decrease to less than one atom per month for the heaviest species. Half-lives range down to below microseconds. The elements at the top of the nuclear chart have been discovered on the basis of single-atom decays after separation in-flight. The production and investigation of the transactinide elements with Z = 104 and beyond form the subject matter of this chapter. After a brief history of their discoveries and experimental methods, nuclear structure and the production of heavy elements will be discussed. The prospects for the synthesis and investigation of heavy elements using advanced technologies such as new high-current heavy-ion accelerators, radioactive beams, and ion traps will be outlined. The importance of closed nuclear shells for the existence and production of the heaviest elements will be addressed briefly.