Search for elements 119 and 120

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.