In a collaboration between FLNR Dubna, Russia, LLNL Livermore, USA and PSI/UBe, Switzerland two new elements of the periodic table have been discovered by a combination of physical and chemical techniques.
In the physics experiment, using a gas-filled magnetic separator, 3 atoms of presumably element 115 were detected that decayed by consecutive a-emissions to element 105 (dubnium) (right side). These atoms were formed in the fusion reaction between ⁴⁸Ca projectiles and a ²⁴³Am target. The formed isotope of Db with mass number 268 did exhibit a very long half-life of 16 hours. Therefore, an additional chemical experiment was conducted to isolate and identify Db. All products recoiling from the target were collected in a copper catcher (left side). Once a day the copper catcher was chemically processed applying liquid chromatography techniques. Final samples were assayed for spontaneous-fission decay in coincidence with prompt neutrons. Fifteen atoms of dubnium were observed in these chemical fractions. The decay pattern of these 15 atoms was in full agreement with those observed from the physics experiment, thus supporting the assignment of the first members of the decay chain to the new, yet undiscovered elements with atomic numbers 115 and its first progeny element 113. The elements below atomic number 111 are all known, though other isotopes than those found in this experiment. The result of this study will be submitted to IUPAC for approval of two new elements of the periodic table.

This work was carried out in the group of Prof. Heinz W. Gäggeler.

References:

• Yu. Ts. Oganessian, V. K. Utyonkov, S. N. Dmitriev, Yu. V. Lobanov, M. G. Itkis, A. N. Polyakov, Yu. S. Tsyganov, A. N. Mezentsev, A. V. Yeremin, A. A. Voinov, E. A. Sokol, G. G. Gulbekian, S. L. Bogomolov, S. Iliev, V. G. Subbotin, A. M. Sukhov, G. V. Buklanov, S. V. Shishkin, V. I. Chepigin, G. K. Vostokin, N. V. Aksenov, M. Hussonois, K. Subotic, V. I. Zagrebaev, K. J. Moody, J. P. Patin, J. F. Wild, M .A. Stoyer, N. J. Stoyer, D. A. Shaughnessy, J. M. Kenneally, P. A. Wilk, R. W. Lougheed, H. W. Gäggeler, D. Schumann, H. Bruchertseifer, R. Eichler;
  "Synthesis of elements 115 and 113 in the reaction ²⁴³Am + ⁴⁸Ca"
  Phys. Rev. C, 72, 034611/1-16, (2005); doi:10.1103/PhysRevC.72.034611.