, Volume 333, Issue 2, pp 163-175

Element 107

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We identified twoα-emitting isotopes of element 107 with masses of 261 and 262 respectively by parent-daughter correlations. For the isotope with mass 262 we found two transitions with (102±26) ms and (8.0±2.1) ms half-life, which we assign to the groundstate and to an isomeric transition, respectively. The half-life of the isotope with mass 261 is (11.8 −2.8 +5.3 ) ms. Spontaneous fission, which could be assigned to the decay of an isotope of element 107, was not detected in our experiments. This observation is in-line with our previous results, indicating a region of nuclei with strong microscopic stabilisation in the trans-actinides. Both new isotopes were produced by complete fusion of209Bi with54Cr. The production cross sections are (163±34) pb for262107 and (36 −14 +22 ) pb for261107.

On leave form Warsaw University, Warsaw, Poland
The authors thank G. Berthes, P. Lemmertz, and M. Montoya for their help during the experiment. They also thank N. Angert and the UNILAC staff for the excellent performance of the accelerator. We are indebted to M. Müller and W. Jacoby for the development of the highly efficient sources for isotopically enriched material and W. Hartmann, J. Klemm, and W. Thalheimer for the skilful preparation of the large area Bi-targets. Further we are endebted 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 set-ups for the SHIP experiments.