Search for elements 119 and 120
J. Khuyagbaatar, A. Yakushev, Ch. E. Düllmann, D. Ackermann, L.-L. Andersson, M. Asai, M. Block, R. A. Boll, H.S. Brand, D. M. Cox, M. Dasgupta, X. Derkx, A. Di Nitto, Κ. Eberhardt, J. Even, M. Evers, C. Fahlander, U. Forsberg, J. M. Gates, N. Gharibyan, P. Golubev, Κ. Ε. Gregorich, J. H. Hamilton, W. Hartmann, R.-D. Herzberg, F. P. Heßberger, D. J. Hinde, J. Hoffmann, R. Hollinger, A. Hübner, E. Jäger, B. Kindler, Jens Volker Kratz, J. Krier, N. Kurz, M. Laatiaoui, Susanta Lahiri, R. Lang, B. Lommel, Moumita Maiti, K. Miernik, S. Minami, A. Mistry, C. Mokry, H. Nitsche, J. P. Omtvedt, G. K. Pang, P. Papadakis, Dennis Renisch, J. B. Roberto, D. Rudolph, J. Runke, K. P. Rykaczewski, L. G. Sarmiento, M. Schädel, Β. Schausten, A. Semchenkov, D. A. Shaughnessy, P. Steinegger, J. Steiner, E. E. Tereshatov, P. Thörle-Pospiech, K. Tinschert, T. Torres De Heidenreich, Ν. Trautmann, Α. Türler, J. Uusitalo, M. Węgrzecki, N. Wiehl, Shelley M. Van Cleve, V. Yakusheva
Abstract
A search for production of the superheavy elements with atomic numbers 119 and 120 was performed in the $^{50}\mathrm{Ti}+^{249}\mathrm{Bk}$ and $^{50}\mathrm{Ti}+^{249}\mathrm{Cf}$ fusion-evaporation reactions, respectively, at the gas-filled recoil separator TASCA at GSI Darmstadt, Germany. Over four months of irradiation, the $^{249}\mathrm{Bk}$ target partially decayed into $^{249}\mathrm{Cf}$, which allowed for a simultaneous search for both elements. Neither was detected at cross-section sensitivity levels of 65 and 200 fb for the $^{50}\mathrm{Ti}+^{249}\mathrm{Bk}$ and $^{50}\mathrm{Ti}+^{249}\mathrm{Cf}$ reactions, respectively, at a midtarget beam energy of ${E}_{\mathrm{lab}}=281.5$ MeV. The nonobservation of elements 119 and 120 is discussed within the concept of fusion-evaporation reactions including various theoretical predictions on the fission-barrier heights of superheavy nuclei in the region of the island of stability.