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  • 23.60.+e  (4)
  • 1
    ISSN: 1434-601X
    Keywords: 23.60.+e ; 25.70.3f ; 25.85.Ca ; 27.9.+6
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract 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.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1434-601X
    Keywords: 21.10.Dr ; 23.60.+e ; 25.70.−z ; 27.90.+b
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In an experiment carried out to identify element 110, we have observed anα-decay chain, that can be unambiguously assigned to269110. In a scries of preexperiments the excitation functions of the fusion reactions50Ti +208Pb→258104* and58Fe +208Pb→266108* were measured with high precision in order to get the optimum projectile energies for the production of these heavy elements. The cross-section maxima of the 1n evaporation channels were observed at excitation energies of 15.6 MeV and 13.4 MeV, respectively. These data result in an optimum excitation energy of 12.3 MeV of the compound nucleus for the production of269110 in the reaction62Ni +208Pb→269110 + 1n. In irradiations at the corresponding beam energy of 311 MeV we have observed a decay chain of 4 subsequent a decays. This can be assigned to the isotope with the mass number 269 of the element 110 on the basis of delayed α-α coincidences. The accurately measured decay data of the daughter isotopes of the elements 108 to 102, obtained in the previous experiments, were used. The isotope269110 decays with a hair-life of (270 -120 +1300 ) μs by emission of (11.132±0.020) MeV alpha particles. The production cross-section is (3.3 -2.7 +6.2 ) pb.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1434-601X
    Keywords: 23.60.+e ; 25.85. Ca ; 25.70. Jj ; 27.90.+b
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Evaporation residues from the heavy-ion fusion reaction50Ti on209Bi were investigated. They were separated from the projectile beam by the velocity filter SHIP and identified after implantation into an array of position-sensitive surface-barrier detectors by analyzing theirα-decay chains. Spontaneous fission was also observed. Four newα emitters,258105 (T1/2=4.4 −0.6 +0.9 s),257105 (T1/2= 1.4 −0.3 +0.6 s),254Lr (T 1/2= 13 −2 +3 s), and253Lr (T 1/2=1.3 −0.3 +0.6 s) could be identified. For the isotope257105 we obtained a spontaneous-fission branch of about 20%. A spontaneous-fission activity with a halflife comparable to that for theα decay of258105 was explained as fission of258104, formed by electron capture from258105. An excitation function for evaporation-residue production was measured for bombarding energies in the range ofE CM=184.4 MeV toE CM=196.6 MeV. Nearly all evaporation residues we observed, could be attributed to the 1n and 2n deexcitation channels. The maximum cross sections wereσ(1n)=c/2.9±0.3) nbarn, andσ(2n)=c/2.1±0.8) nbarn, respectively. We could measure the total kinetic energy of the fission fragments of258104 to be TKE=(220±15) MeV, a value that fits into empirical systematics based on aZ 2/A 1/3 dependence.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1434-601X
    Keywords: 21.10.Dr ; 23.60.+e ; 25.70.−z ; 27.90.+b
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The new element 111 was produced and unambiguously identified in an experiment at SHIP, GSI Darmstadt. Three nuclei of the isotope272111 were observed in irradiations of209Bi targets with64Ni projectiles of 318 MeV and 320 MeV energy. The cross-sections are (1.7 −1.4 +3.3 ) pb and (3.5 −2.3 +4.6 ) pb, respectively. The nuclei decay by a emission into the new and so far the heaviest isotopes of the elements 109 and 107 with mass numbers A=268 and A=264. Theα-decay chains were followed down to the known nuclei260105 and256Lr.
    Type of Medium: Electronic Resource
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