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  • 25.70.Lm  (2)
  • 25.70.JJ  (1)
  • 74.25 Fy  (1)
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Materialart
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  • 1
    Digitale Medien
    Digitale Medien
    Reactions of40Ar with233U,235U, and238U at the barrier (1990)
    Springer
    The European physical journal 335 (1990), S. 421-430 
    Details
    ISSN: 1434-601X
    Schlagwort(e): 25.70.CD ; 25.70.JJ ; 25.70.LM
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Production cross sections for target-like transfer products in reactions of40Ar with233,235,238U at the barrier were determined using radiochemical techniques. The heaviest products detected are isotopes of californium (Z=98). In addition to the quasi-elastic component of the isotopic distributions observed in the vicinity of uranium, there are also relaxed contributions throughout the entire region. The peak positions of the isotope distributions of this component for fixed atomic number, after the transfer of 〉 3 charges, approach closely the minimum of the potential energy surfaces (PES). The experimental results thus indicate the cold formation of the reaction products. A search for long-lived heavy actinides produced, by fusion-evaporation, via isotopes of element 110 and their subsequent decay through α-decay chains, remained unsuccessful at a cross section limit of 21 pb.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01290190
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  • 2
    Digitale Medien
    Digitale Medien
    Competition between binary reactions and fusion in heavy-ion collisions at the Coulomb barrier (1992)
    Springer
    The European physical journal 342 (1992), S. 411-427 
    Details
    ISSN: 1434-601X
    Schlagwort(e): 25.70.Cd ; 25.70.Jj ; 25.70.Lm
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Mass and charge distributions for binary reaction channels have been measured for the reactions86Kr with76Ge,104Ru and130Te at the Coulomb barrier using chemical separations andγ-ray spectroscopy. These systems span the region where dynamical hindrance to complete fusion sets in. The binary reactions can be subdivided into two components associated withi) reflection from the outer potential barrier (quasielastic), andii) reseparation after passing the barrier (complex reactions). The sum of complex-reaction channels and evaporation residues from complete fusion can be reproduced by a barrier passing calculation. The fraction of the barrier passing flux leading to reseparation increases from 26±10% for the lightest system to more than 90% for the heaviest system. The data indicate that fusion hindrance is primarily caused by reseparation shortly after passage of the barrier before Swiatecki's conditional saddlepoint is overcome, resulting in partitions close to the entrance channel configuration. In addition, for the heaviest system, a quasifission component representing somewhat less than 20% of the barrier-passing flux was observed. From the missing masses of fragment pairs we can deduce that the reseparating complex-reaction products have kinetic energies well below the fusion barrier and share the excitation energy in a way similar to the sawtooth-like curve known from low-energy fission. The quasielastic, predominantly one- and two-nucleon transfer channels, have strongly varying cross sections for the three systems despite similar effectiveQ-values. A systematics of one-neutron transfer cross sections at the Coulomb barrier is established and shown to differ considerably from the smooth behaviour observed at energies 20–30% above the barrier. The connection to nuclear polarization phenomena and orbit matching is pointed out.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01294952
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  • 3
    Digitale Medien
    Digitale Medien
    Cross sections for nuclear reactions in collisions of238U+238U and238U +197Au near and below the coulomb barrier (1991)
    Springer
    The European physical journal 340 (1991), S. 303-314 
    Details
    ISSN: 1434-601X
    Schlagwort(e): 25.70.CD ; 25.70.Lm ; 25.85.−W
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Cross sections for nuclear reactions at beam energies near and below the spherical Coulomb barrier V c were measured in the very heavy collision systems238U +238U and238U +197Au. The most probable reaction channel with mass transfer is the one-neutron transfer. Its excitation function is understood in terms of Rutherford trajectories together with the quantal process of neutron tunnelling over large distances. In addition, the exchange of up to 15 nucleons is observed down to 0.90 V c . The excitation functions for the multi-nucleon transfer products have much steeper slopes than that for one-neutron transfer, and are steeper for238U +197Au than for238U +238U, suggesting that nuclear contact is established in the associated collisions. The angular distribution for one selected multi-nucleon transfer product,227Th, shows that its formation occurs in more central collisions within contact times shorter than about 10−21 s. There is no evidence for very longlived di-nuclear systems in the these reactions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01294679
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  • 4
    Digitale Medien
    Digitale Medien
    Vortex dynamics in Bi2Sr2CaCu2O8-thin films in the presence of columnar defects (1996)
    Springer
    Journal of low temperature physics 105 (1996), S. 1153-1158 
    Details
    ISSN: 1573-7357
    Schlagwort(e): 74.25 Fy ; 74.60 Ge ; 74.60 Jg ; 74.72 Hs
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract With heavy ion irradiation we create continous amorphous columnar defects in Bi2Sr2CaCu2O8-thin films. With regard to a reliable comparison of irradiation effects three of four identical striplines on the same samples were exposed to different irradiation procedures. We performed irradiations as well parallel as under different angles with respect to the film $$\vec c$$ -axis. Beside an enlarged normal state resistivity after irradiation the films suffer a Tc-reduction proportional to the volume of the damaged material. The activation energy ascertained from resistive transitions shows best enhancement for magnetic field values close to the matching field. Measurements of the transport critical current density, the activation energy and the irreversibility field in different field orientations show no anisotropic flux pinning due to the induced columnar defects. This can be explained by the two dimensional behaviour of the Bi2Sr2CaCu2O8-thin films.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00753855
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