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  • 1985-1989  (5)
Material
Years
  • 1985-1989  (5)
Year
  • 1
    ISSN: 1434-601X
    Keywords: 23.60.+ e ; 25.70.Jj ; 27.9.+b
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: 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 −0.7 +2.2 ) 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 −36 +364 ) μs. Our experimental results point towards an enhanced stability of the heaviest elements against spontaneous fission, which was already observed for element 106.
    Type of Medium: Electronic Resource
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  • 2
    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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  • 3
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The reactions58Ni+102Pd→160W and58Ni+106Cd→164Os were investigated to search for new decay data of neutron deficient nuclei. Excitation energies of the compound nuclei covered a range from 47 to 89 MeV. Velocity separation of the evaporation residues and position time correlations with the a decays of the implanted nuclei were used. The following new decay data were measured:162Os (Eα=(6611 ±30) keV, T1/2=(1.9±0.7) ms);158W (T1/2=(0.9±0.3) ms);158mW (E=1.88 MeV, Eα=(8280±30) keV, T1/2=(0.01-1) ms);155mLu (Eα=(5575±10) keV); β decay of156Ta (T1/2 〉 10 ms) to the 8+ yrast isomer in156Hf. A cross section of 5μb was measured for the new isotope156Ta produced in a p3n evaporation channel from160W at 64 MeV excitation energy.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Conclusion We have observed the decay of one atom of the doubly even isotope 108. We observed α-decay with a halflife, of (76 −36 +364 ) Μs. The full α-decay energy could not be measured, as the α escaped the detector. With the knowledge of the halflife, an estimate on the α-decay energy can be made. From the formula of Rasmussen9 and a reduced α-width of 1, a value which has been measured for260106 and also for the doubly even isotones of N=156, we obtain Q=(11.0 −0.3 +0.1 MeV. This value is higher than given by Moeller10 (10.35 MeV), and agrees with that of Uran and Zeldes11 (10.9 MeV). A hindrance factor wα of 0.5 increases the Qα-value by 0.14 MeV. The mass excess of264108 follows as (120.0±0.3) MeV. The groundstate shell effect amounts to (−5.0±0.3) MeV using the macroscopic mass values of Ref. 10. The formation cross section of (3.2 −2.6 +6.1 ) pb overlaps with the value of ∼ 5 pb from Dubna for the 6 ms sf-activity mentioned initially but is considerably lower than an extrapolation from the reaction58Fe (208Pb,n)265108 which gave 10 pb with the lower limit of 4 pb.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 325 (1986), S. 37-43 
    ISSN: 1434-601X
    Keywords: 23.20.Lv ; 29.30.Cm ; 28.60.+s
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Fusion evaporation reactions were investigated to search for short lived isomeric states of nuclei near the proton drip line. Gamma spectra were measured, both singles and in delayed coincidence with evaporation residues implanted into a silicon detector after a velocity separation. A short lived activity was measured in the40Ca+40Ca →80Zr* reaction at excitation energies between 55 and 79 MeV. A half-life of 3.20 (10) μs was determined from delayed coincidences between evaporation residues and gamma rays. AtE *=55 MeV the cross section is 9 mb. The activity was assigned to an isomeric state in76Rb by investigation of excitation functions. The isomer decays by emission of four gamma rays with energies of 70.55(5), 101.30(4), 145.11 (5), and 246.32(10) keV. A first level scheme is proposed assigning to the isomeric state an energy of 316.94(7) keV above the ground state. The isomer decaying into the low spin 1(−) ground state band is explained from systematics as a band head of a high spin (4+) (πg9/2,νg9/2) structure. A high hindrance factor of 3×106 forE1 radiation compared to a single particle transition is due possibly to a change of the core particle structure in the transition.
    Type of Medium: Electronic Resource
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