A. V. Ramayya, Kenton J. Moody, D. A. Shaughnessy, J. M. Gostic, Rose A. Boll, A. A. Voinov, R. N. Sagaidak, M. A. Stoyer, A. M. Sukhov, K. P. Rykaczewski, Julie G. Ezold, Yu. Ts. Oganessian, J. H. Hamilton, M. A. Ryabinin, F. Sh. Abdullin, M. G. Itkis, J. Binder, C.W. Alexander, Yu. S. Tsyganov, K. Miernik, A. N. Polyakov, Robert Grzywacz, I. V. Shirokovsky, K. Felker, N. J. Stoyer, Roger Henderson, V. G. Subbotin, V. K. Utyonkov, David Miller, M. V. Shumeiko, James B. Roberto, Grigory K. Vostokin, and S. N. Dmitriev
The reaction of 249Bk with 48Ca has been investigated with an aim of synthesizing and studying the decay properties of isotopes of the new element 117. The experiments were performed at five projectile energies (in two runs, in 2009-2010 and 2012) and with a total beam dose of 48Ca ions of about 9x1019 The experiments yielded data on a-decay characteristics and excitation functions of the produced nuclei that establish these to be 293117 and 294117 – the products of the 4n- and 3n-evaporation channels, respectively. In total, we have observed 20 decay chains of Z=117 nuclides. The cross sections were measured to be 1.1 pb for the 3n and 2.4 pb for the 4n-reaction channel. The new 289115 events, populated by α decay of 117, demonstrate the same decay properties as those observed for 115 produced in the 243Am(48Ca,2n) reaction thus providing cross-bombardment evidence. In addition, a single decay of 294118 was observed from the reaction with 249Cf – a result of the in-growth of 249Cf in the 249Bk target. The observed decay chain of 294118 is in good agreement with decay properties obtained in 2002-2005 in the experiments with the reaction 249Cf(48Ca,3n)294118. The energies and half-lives of the odd-Z isotopes observed in the 117 decay chains together with the results obtained for lower-Z superheavy nuclei demonstrate enhancement of nuclear stability with increasing neutron number towards the predicted new magic number N=184.