Abstract
The experiment having led to the discovery of first isotopes of element 108, as published previously in Short Notes to this Journal [1, 2] are described and discussed in a final paper.
Two isotopes of element 108 were produced by complete fusion of207Pb and208Pb, respectively, with58Fe. Both isotopes areα-emitters.
For the isotope with mass 265 threeα-decay sequences were observed. Theα-decay energy is (10.36±0.03) MeV, the half-life (1.8 +2.2−0.7 ) ms. For the isotope with mass 264, which is the heaviest doubly even isotope known at present, the decay sequence of one atom was found. The measured half-life is (76 +364−36 ) μs.
Our experimental results point towards an enhanced stability of the heaviest elements against spontaneous fission, which was already observed for element 106.
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The authors thank N. Angert and UNILAC staff for the excellent performance of the accelerator. We are indebted to W. Jacoby and M. Müller for the development of the highly-efficient sources for enriched material, and W. Hartmann and W. Thalheimer for the skilful preparation of the large-area Pb-targets. Further we are indebted to the GSI experimental electronics group, namely M. Richter for their helpful assistance. We also thank H.G. Burkhard, who is in charge of the mechanical setups at SHIP. One of the autors (M.E. Leino) expresses his gratitude to GSI for kind hospitality.