Recoil techniques in the study of transactinide elements. Discovery of new elements and hot atom chemistry

Hot atom chemistry has been of vital importance in the separation and discovery of the heaviest elements. Recoil techniques have been used in the discovery of all the heavy elements from mendelevium (101) through element 109, the heaviest currently known. In this 'recoil' method a relatively thin target is deposited on an appropriate backing and the projectile beam from the accelerator first passes through the backing and then into the target. The recoiling products can subsequently be collected or transported in a variety of ways. In our studies of the nuclear and chemical properties of the transactinides, gas transport systems incorporating helium gas and aerosols (KCl, NaCl, MoO3) have been used. This method is rapid (fractions of a second) and highly efficient and has been used in both our aqueous and gaseous phase studies of heavy actinides and transactinides as well as to deposit recoiling activities directly on thin foils held on a rotating wheel for spontaneous fission and alpha measurements. A few examples of our studies on the chemical and nuclear properties of elements 104 and 105 will be discussed. (author)