arXiv subjects

K. Hagino

Publications and source records attributed to K. Hagino.

222 records · Page 13Linked to original sources

arXiv1997

Adiabatic quantum tunneling in heavy-ion sub-barrier fusion

High precision measurements of the fusion excitation functions for the reactions ^{40}Ca + ^{194}Pt, ^{192}Os clearly demonstrate that projectile excitation significantly modifies the potential barrier distribution. In sharp contrast, fusion of ^{16}O + ^{144}Sm appears to show no influence of the projectile excitation on the shape of the barrier distribution. These apparently conflicting conclusions are reconciled in this work, using realistic coupled--channels calculations, which show that high energy states produce an adiabatic potential renormalisation. This result indicates that adiabatic effects restrict, in a natural way, the states which influence the shape of a fusion barrier distribution. The analysis of barrier distributions thus offers a criterion for the relevance of the `counter term' prescription in the Caldeira-Leggett approach.

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arXiv1996

Validity of the linear coupling approximation in heavy-ion fusion reactions at sub barrier energies

The role of higher order coupling of surface vibrations to the relative motion in heavy-ion fusion reactions at near-barrier energies is investigated. The coupled channels equations are solved to all orders, and also in the linear and the quadratic coupling approximations. Taking $^{64}$Ni + $^{92,96}$Zr reactions as examples, it is shown that all order couplings lead to considerably improved agreement with the experimentally measured fusion cross sections and average angular momenta of the compound nucleus for such heavy nearly symmetric systems. The importance of higher order coupling is also examined for asymmetric systems like $^{16}$O + $^{112}$Cd, $^{144}$Sm, for which previous calculations of the fusion cross section seemed to indicate that the linear coupling approximation was adequate. It is shown that the shape of the barrier distributions and the energy dependence of the average angular momentum can change significantly when the higher order couplings are included, even for systems where measured fusion cross sections may seem to be well reproduced by the linear coupling approximation.

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arXiv1995

Non-adiabatic effect in electron screening in fusion reactions at astrophysical energies

We calculate the electron screening effect in low energy nuclear fusion reactions by taking non-adiabaticity of the tunnleing process into account. In order to investigate deviations from the adiabatic limit, we use the dynamical norm method, which has recently been developed by the present authors. Using $d$+D reaction as an example, we show that the screening energy never exceeds those estimated in the adiabatic approximation. Our calculations indicate that the non-adiabatic effect is important both in classically allowed and classically forbidden processes.

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arXiv1995

Thermal fission rate around super-normal phase transition

Using Langer's $Im F$ method, we discuss the temperature dependence of nuclear fission width in the presence of dissipative environments. We introduce a low cut-off frequency to the spectral density of the environmental oscillators in order to mimic the pairing gap. It is shown that the decay width rapidly decreases at the critical temperature, where the phase transition from super to normal fluids takes place. Relation to the recently observed threshold for the dissipative fission is discussed.

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arXiv1995

Effects of mass renormalization on the surface properties of heavy-ion fusion potential

We discuss the effects of fast nuclear excitations on heavy-ion fusion reactions at energies near and below the Coulomb barrier. Using the fusion of two $^{40}$Ca nuclei as an example and the inversion method, we show that the mass renormalization induced by fast nuclear excitations leads to a large surface diffuseness in the effective potential for heavy-ion fusion reactions.

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arXiv1995

Path integral approach to no-Coriolis approximation in heavy-ion collisions

We use the two time influence functional method of the path integral approach in order to reduce the dimension of the coupled-channels equations for heavy-ion reactions based on the no-Coriolis approximation. Our method is superior to other methods in that it easily enables us to study the cases where the initial spin of the colliding particle is not zero. It can also be easily applied to the cases where the internal degrees of freedom are not necessarily collective coordinates. We also clarify the underlying assumptions in our approach.

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