Results 1 - 10 of 1155
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[en] The nuclear photo-emulsion method makes it possible to study in detail the fragmentation of a projectile thanks to a high resolution capability of emulsion and the detection of secondaries in a 4π geometry. The registration of all charged particles and their identification enable one to explore the isotopic composition of fragments and the projectile fragmentation channels. In the paper are presented results on an investigation of 8B interactions with photo-emulsion nuclei. A detailed analysis made it possible to justify selections of events of nuclear fragmentation 8B→2He + p.
[en] The Coulomb dissociation of 8B on high-Z targets can be described by first-order perturbation theory at high beam energies but the far-field approximation, which is commonly used, becomes inaccurate at impact parameters less than ∼25 fm. The leading-order correction at lower beam energies is a dynamic polarization effect, which reduces the dissociation probability. The relative significance of the effect scales roughly as Z/E in terms of the target charge Z and beam energy E. The reduction due to a destructive Coulomb-nuclear interference, on the other hand, is rather modest
[en] Coulomb dissociation has been proposed on many occasions as a means of determining the interaction between fragments at low relative energies. For the case of 8B the main motivation has been the determination of the S17. This method is briefly reviewed from a theoretical point of view, and the validity of certain approximations is discussed, focussing on the sub-Coulomb Notre Dame (ND) regime
[en] We investigate the validity of the semiclassical approximation for the breakup of weakly bound nuclei. For this purpose, we calculate angular distributions in the breakup of 8B in the 8B+58Ni collision at sub-barrier energies and compare the results with those of a quantum mechanical calculation available in the literature. We show that the semiclassical results are very close to those obtained by quantum mechanics
[en] Continuum couplings are extremely important to describe the breakup of loosely bound nuclei. We explore the various methods of extracting a polarization potential, as an effective representation of these couplings in the breakup channel. Our application consists of 8B→7Be+p on 58Ni at near-barrier energies. We find that the standard ways of determining polarization potentials are not useful to describe the breakup cross section in terms of a one-step process. Our results indicate that continuum couplings are strongly non-local and the complexity of coupled channel methods may well be unavoidable
[en] We present an accurate method of simultaneously treating nuclear and Coulomb breakup of weakly bound nuclei by means of the method of continuum discretized coupled channels with the pseudostate method of discretization. As L2-type basis functions of expansion of bound and continuum states of the projectile, we take complex-range Gaussian functions which in good approximation form a complete set in a large configuration space which is important for both nuclear- and Coulomb-breakup processes. The accuracy of the method is tested quantitatively for 8B+58Ni scattering at 25.8 MeV
[en] One of the most striking features of drip line nuclei is their very low binding energy. The proximity to threshold implies that many of the standard reactions should take into account the possibility of the nucleus breaking up into the continuum and rearranging itself within the continuum, throughout the reaction process. Whereas for stable nuclei often structure could be factorized out of the reaction model, it is clear that for exotic nuclei, the specific structure features cannot be des entangled. We review a variety of different cases where the coupling to the continuum and between continuum states was shown to be crucial for the understanding of the physical phenomena. Breakup reactions of 8 B, for various energies and on a few targets, are discussed. The effect of the continuum on the elastic cross sections as well as transfer and fusion processes is also presented. (author)
[en] We report the first detailed study of the relative importance of the stripping and diffraction mechanisms involved in nucleon knockout reactions, by the use of a coincidence measurement of the residue and fast proton following one-proton knockout reactions. The measurements used the S800 spectrograph in combination with the HiRA detector array at the NSCL. Results for the reactions 9Be(9C,8B+X)Y and 9Be(8B,7Be+X)Y are presented and compared with theoretical predictions for the two reaction mechanisms calculated using the eikonal model. The data show a clear distinction between the stripping and diffraction mechanisms and the measured relative proportions are very well reproduced by the reaction theory. This agreement adds support to the results of knockout reaction analyses and their applications to the spectroscopy of rare isotopes.
[en] The impact of global acoustic modes on the 8B neutrino flux time series is computed for the first time. It is shown that the time fluctuations of the 8B neutrino flux depend on the amplitude of acoustic eigenfunctions in the region where the 8B neutrino flux is produced: modes with low n (or order) that have eigenfunctions with a relatively large amplitude in the Sun's core strongly affect the neutrino flux; conversely, modes with high n that have eigenfunctions with a minimal amplitude in the Sun's core have a very small impact on the neutrino flux. It was found that the global modes with a larger impact on the 8B neutrino flux have a frequency of oscillation in the interval 250 μHz to 500 μHz (or a period in the interval 30 minutes to 70 minutes), such as the f-modes (n = 0) for the low degrees, radial modes of order n ≤ 3, and the dipole mode of order n = 1. Their corresponding neutrino eigenfunctions are very sensitive to the solar inner core and are unaffected by the variability of the external layers of the solar surface. If time variability of neutrinos is observed for these modes, it will lead to new ways of improving the sound speed profile inversion in the central region of the Sun