Angular distributions in quasi-fission reactions

Lützenkirchen, K.; Kratz, J. V.; Wirth, G.; Brüchle, W.; Sümmerer, K.; Lucas, R.; Poitou, J.; Grégoire, C.

doi:10.1016/0375-9474(86)90312-x

Cited by 32 publications

(41 citation statements)

References 33 publications

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“…Thus it appears that in contrast to the two lighter systems, the evolution behind the potential barrier can be followed beyond the conditional saddle point for the Kr + Te system. A more detailed study of the angular evolution as a function of well resolved nuclear charge and/or mass [30,31] would be helpful to further corroborate this point.…”

Section: Complex Reaction Channels: the Fate Behind The Barriermentioning

confidence: 62%

Competition between binary reactions and fusion in heavy-ion collisions at the Coulomb barrier

Reisdorf¹,

Kratz

Bellwied

et al. 1992

Z. Physik A - Hadrons and Nuclei

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Mass and charge distributions for binary reaction channels have been measured for the reactions 86Kr with 76Ge, I~ and 13~ at the Coulomb barrier using chemical separations and 7-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 with i) reflection from the outer potential barrier (quasielastic), and ii) 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 effective Q-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 barri- er. The connection to nuclear polarization phenomena and orbit matching is pointed out.

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Section: Complex Reaction Channels: the Fate Behind The Barriermentioning

confidence: 62%

Competition between binary reactions and fusion in heavy-ion collisions at the Coulomb barrier

Reisdorf¹,

Kratz

Bellwied

et al. 1992

Z. Physik A - Hadrons and Nuclei

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“…with increasing mass-(charge-) flow, but did not reach saturation, thus indicating the absence of any kind of a steady state. For the majority of the cross sections the values of K z were even smaller [18] than predicted in an extreme scission-point model [19]. The latter are again significantly smaller than equilibrium values calculated in the rigid-rotor transition-state theory at the fission-saddle point.…”

Section: Introductionmentioning

confidence: 70%

“…Liitzenkirchen et al [3,18] analyzed such Z-dependent angular distributions, d 2 ~/dZ dO, of the quasi-fission type in reactions of S~ and 56Fe with 2~ near the fusion barrier in terms of a direct reaction theory [19] and found low values for the variance of the tilting angular momentum, K 2, that were dynamically increasing with time, i.e. with increasing mass-(charge-) flow, but did not reach saturation, thus indicating the absence of any kind of a steady state.…”

Section: Introductionmentioning

confidence: 98%

“…The latter are again significantly smaller than equilibrium values calculated in the rigid-rotor transition-state theory at the fission-saddle point. Lfitzenkirchen et al [18] For systems lighter than Ti or Fe + Pb one might expect [2] that the life-times of the reaction intermediates become longer, so that the observation of forward-backward asymmetries in the angular distributions due to quasi-fission contributions may become more difficult. The angular distributions may even become perfectly symmetric around 0 = 90 ~ if the lifetime of the quasi-fission complex becomes distinctly larger than the rotational period.…”

Section: Introductionmentioning

confidence: 98%

“…Then, the presence of short-lived non-compound systems is sensitively indicated by left-right asymmetries [1,2] in the mass distribution at a fixed scattering angle 0, and by forwardbackward asymmetries [3,18] in the angular distributions at fixed fragment charge Z.…”

Section: Introductionmentioning

confidence: 99%

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Evidence for quasi-fission in40Ar+208Pb collisions near the coulomb-barrier

Keller

Lützenkirchen

Kratz

et al. 1987

Z. Physik A - Atomic Nuclei

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Fission-fragment angular distributions were measured in the reaction of 4~ with 2~ near the fusion barrier. For nearly symmetric mass-/charge splits we find angular distributions symmetric around 0 = 90 degrees, however, with unusually large anisotropies. These develop gradually into forward-backward asymmetric distributions as one moves away from mass-/charge symmetry. This indicates that non-compound fission ('quasi-fission') competes with true fusion-fission. The relative contribution of quasi-fission to the total fission cross section is somewhere between 51 and 85%. In the framework of the extrapush model this is equivalent to an extra-extra push energy for compound-nucleus formation inside the true fission saddle point of 4 < Exx < 9 MeV in agreement with a recent empirical parametrization of fusion-barrier shifts based on fusion-fission cross sections. On the basis of cross sections for fusion-evaporation residues it had previously been concluded that fusion of 4~ with Pb isotopes occurs unhindered. Possible reasons for this apparent discrepancy are discussed. PACS: 25.70.Jj

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Nuclear Reactions

2013

Nuclear and Radiochemistry

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Angular distributions in quasi-fission reactions

Cited by 32 publications

References 33 publications

Competition between binary reactions and fusion in heavy-ion collisions at the Coulomb barrier

Competition between binary reactions and fusion in heavy-ion collisions at the Coulomb barrier

Evidence for quasi-fission in40Ar+208Pb collisions near the coulomb-barrier

Nuclear Reactions

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