We study the bremsstrahlung radiation of a tunneling charged particle in a time-dependent picture. In particular, we treat the case of bremsstrahlung during alpha-decay, which has been suggested as a promissing tool to investigate the problem of tunneling times. We show deviations of the numerical results from the semiclassical estimates. A standard assumption of a preformed particle inside the well leads to sharp high-frequency lines in the bremsstrahlung emission. These lines correspond to "quantum beats" of the internal part of the wavefunction during tunneling arising from the interference of the neighboring resonances in the well.

The velocity dependence of the stopping power of swift protons and deuterons in low energy collisions is investigated. At low projectile energies the stopping is mainly due to nuclear stopping and charge exchange of the electron. The second mechanism dominates after E p ≥ 200 eV. A dynamical treatment of the charge exchange mechanism based on two-center electronic wavefunctions yields very transparent results for the exchange probability. We predict that the stopping cross sections vary approximately as v 1.35 p for projectile protons on hydrogen targets in the 1 keV energy region.Nuclear fusion reactions proceed in stars at extremely low energies, e.g., of the order of 10 keV in our sun [1,2]. At such low energies it is extremely difficult to measure the cross sections for charged particles at laboratory conditions due to the large Coulomb barrier. One often uses a theoretical model to extrapolate the experimental data to the low-energy region. Such extrapolations are sometimes far from reliable, due to unknown features of the low-energy region. E.g., there might exist unknown resonances along the extrapolation, or even some simple effect which one was not aware of before. One of these effects is the laboratory atomic screening of fusion reactions [3,4]. It is well known that the laboratory measurements of low energy fusion reactions are strongly influenced by the presence of the atomic electrons. This effect has to be corrected for in order to relate the fusion cross sections measured in the laboratory with those at the stellar environment. Another screening effect, arising from free electrons in the stellar plasma, will not be treated here. For about one decade, until 1996, one observed a large discrepancy between the experimental data and the best models available to treat the screening effect. The simplest (and perhaps the best of these models), the so-called adiabatic model, predicts that as the projectile nucleus penetrates the electronic cloud of the target the electrons become more bound and the projectile energy increases by energy conservation. Since the fusion cross sections increase strongly with the projectile's energy, this tiny amount of energy gain (of order of 10-100 eV) leads to a large effect on the measured cross sections. However, in order to explain the experimental data, it is necessary an extraamount of energy -about twice the value obtained by the adiabatic model. This is

The role of anharmonic effects on the excitation of the double giant dipole resonance is investigated in a simple macroscopic model.Perturbation theory is used to find energies and wave functions of the anharmonic ascillator.The cross sections for the electromagnetic excitation of the one- and two-phonon giant dipole resonances in energetic heavy-ion collisions are then evaluated through a semiclassical coupled-channel calculation.It is argued that the variations of the strength of the anharmonic potential should be combined with appropriate changes in the oscillator frequency,in order to keep the giant dipole resonance energy consistent with the experimental value.When this is taken into account,the effects of anharmonicities on the double giant dipole resonance excitation probabilities are small and cannot account for the well-known discrepancy between theory and experiment

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