In bombarding
209Bi and
207, 208Pb targets by
55Mn and
58Fe ions the yields of
cold fusion
reactions have been determined using a sensitive technique for detecting
T
1/2
1 ms spontaneous fission and the
-decay of heavy actinide elements. It has been shown that the
A = 263–265 isotopes of element 108, including the even-even isotope
264108, undergo mainly
-decay. The obtained results, together with the known data on the properties of the isotopes of elements 104 and 106, provide evidence for the enhanced stability of the
Z=108 nuclei against spontaneous fission.
We are deeply grateful to Academician G.N. Flerov for his attention to this work, for valuable advice and comments. We are thankful to G.G. Gulbekyan, B.A. Gikal, V.B. Kutner for providing intense heavy ion beams during prolonged irradiations, V.G. Subbotin, V.M. Plotko, I.V. Kolesov, G.N. Ivanov, O.K. Nefedyev, I.A. Kharitonova for their help in developing the experimental equipment, J. Esteves, A.V. Rykhlyuk, S.V. Malutin, K.I. Merkina, L.V. Jolos, M. Constantinescu and L.P. Kulkina for their help in performing the experiment. We also acknowledge the valuable comments of Professor I. Zvara and Yu.A. Lazarev.