The European Physical Journal A - Hadrons and Nuclei

, Volume 12, Issue 1, pp 57-67

First online:

Decay properties of neutron-deficient isotopes 256, 257Db, 255Rf, 252, 253Lr

  • F.P. HeßbergerAffiliated withGesellschaft für Schwerionenforschung mbH, D-64220 Darmstadt, Germany
  • , S. HofmannAffiliated withGesellschaft für Schwerionenforschung mbH, D-64220 Darmstadt, Germany
  • , D. AckermannAffiliated withGesellschaft für Schwerionenforschung mbH, D-64220 Darmstadt, Germany
  • , V. NinovAffiliated withGesellschaft für Schwerionenforschung mbH, D-64220 Darmstadt, Germany
  • , M. LeinoAffiliated withPhysics Department, University of Jyväskylä, FIN-40351 Jyväskylä, Finland
  • , G. MünzenbergAffiliated withGesellschaft für Schwerionenforschung mbH, D-64220 Darmstadt, Germany
  • , S. SaroAffiliated withDepartment of Nuclear Physics, Comenius University, SK-84215 Bratislava, Slovakia
  • , A. LavrentevAffiliated withFlerov Laboratory of Nuclear Reactions, JINR, 141 980 Dubna, Russia
  • , A.G. PopekoAffiliated withFlerov Laboratory of Nuclear Reactions, JINR, 141 980 Dubna, Russia
    • , A.V. YereminAffiliated withFlerov Laboratory of Nuclear Reactions, JINR, 141 980 Dubna, Russia
    • , Ch. StodelAffiliated withGesellschaft für Schwerionenforschung mbH, D-64220 Darmstadt, Germany

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Abstract.

Isotopes of dubnium (element 105) with mass numbers A = 256, 257, and 258 were produced by the reaction 209Bi(50Ti,xn) 259-xDb (x = 1, 2, 3) at projectile energies of (4.59-5.08) AMeV. Excitation functions were measured for the 1n, 2n and 3n evaporation channels. The same position of the excitation function was observed for the 1n channel as for the previously measured 1n channel of the reaction 208Pb(50Ti,1n)257Rf. The measured α-decay data of 257Db and its daughter products resulted in the identification of α-decaying isomeric states in 257Db and 253Lr. Two new isotopes, 256Db and 252Lr, were produced at the highest bombarding energies of 4.97 AMeV and 5.08 AMeV. They were identified by delayed α-α coincidences. The measured half-lives are (1.6+0.5 -0.3) s for 256Db and (0.36+0.11 -0.07) s for 252Lr. Besides α-decay, a spontaneous fission activity of T 1/2 = (2.3+1.1 -0.6) s was observed and attributed to an electron-capture branch of 256Db, which feeds the fissioning nucleus 256Rf. A branching ratio of 0.36±0.12 was obtained. The isotope 255Rf was produced by the reaction 207Pb(50Ti,2n)255Rf. Improved decay data have been obtained by means of α- and α-γ spectroscopy.

PACS. 23.60.+e Alpha decay – 25.70.Jj Fusion and fusion-fission reactions – 25.85.Ca Spontaneous fission – 23.20.Lv Gamma transitions and level energies