Production and Decay of the Heaviest Nuclei ~(293,294)117 and ~(294)118

摘要

Two years after the discovery of element 117, we undertook a second campaign using the ~(249)Bk + ~(48)Ca reaction for further investigations of the production and decay properties of the isotopes of element 117 on a larger number of events. The experiments were started in the end of April 2012 and are still under way. This Letter presents the results obtained in 1200 hours of an experimental run with the beam dose of ~(48)Ca of about 1.5 × 10~(19) particles. The ~(249)Bk target was irradiated at two energies of ~(48)Ca that correspond to the maximum probability of the reaction channels with evaporation of three and four neutrons from the excited ~(297)117. In this experiment, two decay chains of ~(294)117 (3n) and five decay chains of ~(293)117 (An) were detected. In the course of the long-term work, ~(249)Cf-the product of decay of ~(249)Bk (330 d)-is being accumulated in the target. Consequently, in the present experiment, we also detected a single decay of the known isotope ~(294)118 that was produced during 2002-2005 in the reaction ~(249)Cf (~(48)Ca, 3n)~(249)118. The obtained results are compared with the data from previous experiments. The experiments are carried out in the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, using the heavy-ion cyclotron U400.