No abstract available

[en] Using all the available empirical information, we analyze the spacing distributions of low-lying 2⁺ levels of even-even nuclei. To obtain statistically relevant samples, the nuclei are grouped into classes defined by the ratio R_4/2 of the excitation energies of the first 4⁺ and 2⁺ levels. This ratio serves as a measure of collectivity in nuclei. With the help of Bayesian inference, we determine the chaoticity parameter for each class. This parameter is found to vary strongly with R_4/2 and takes particularly small values in nuclei that have one of the dynamical symmetries of the interacting boson model

[en] A model for multinucleon transfer reactions is suggested, according to which the main contribution to the reaction is due to collisions with orbital angular momenta lying between the critical angular momentum for formation of a compound nucleus and the angular momentum of the grazing trajectory. It is shown that the time of such collisions is comparable to the time of flight of the projectile in the field of the target but much longer than the time of nuclear orbiting. An expression is derived for the reaction amplitude on the assumption that different partial waves are allowed to interfere as in the case of a direct reaction and that the partial wave cross sections are proportional to the level density of the given reaction product. The energy spectra calculated with this model are found to agree with the experimental spectra of products of the interaction of 145 MeV ¹⁵N with ²³²Th in those cases in which many nucleons are transferred from the projectile to the target. (auth.)

No abstract available

[en] We assume that the energy spectrum of a chaotic system undergoing symmetry-breaking transitions can be represented as a superposition of independent level sequences, one increasing at the expense of the others. The relation between the fractional level densities of the sequences and the symmetry-breaking interaction is deduced by comparing the asymptotic expression of the level-number variance with the corresponding expression obtained using the perturbation theory. This relation is supported by a comparison with previous numerical calculations. The predictions of the model for the nearest-neighbor-spacing distribution and the spectral rigidity are in agreement with the results of an acoustic resonance experiment

[en] We obtain a closed-form expression for the distribution of fusion barriers for vibrational nuclei using a generalization of Dasso, Landowne, and Winther's model, which represents the nuclear surface vibrations as a number of harmonic oscillators, and allows the excitation of an arbitrary number of phonons in the target and/or projectile. We find that this expression is in reasonable agreement with the average trends of the empirical distributions for the fusion of ¹⁶O with ⁹²Zr, ¹⁴⁴Sm and ²⁰⁸Pb, but fails to reproduce the double peaking of the distribution for the ¹⁴⁴Sm target. Only when we restrict the number of excited phonons to a limited number, we are able to reproduce such discrete structures. We show that limiting the number of coupled channels, particularly in the case of strong coupling, increases the spacings between the channel eigenvalues that determine the positions of the peaks of the barrier distribution and modifies their heights. (orig.)

[en] It is shown that cross sections describing deep inelastic collisions between complex nuclei can neither be described as a coherent nor as an incoherent superposition of partial-wave amplitudes. The number of interfering partial waves increases with the masses of the interacting nuclei and decreases with the interaction time. (Auth.)

[en] An analytic continuation of the s matrix into the complex 1 plane is performed. A smooth cut-off representation for the s matrix is parametrized so that its pole nearest to the real axis dominates the elastic scattering of strongly absorbed particles. An application to α particle elastic scattering data gives information about the nature of the pole trajectory. A description of the back-angle anomalies, their energy dependence and the isotope effect is presented. (author)

[en] We study the interaction between collective and single-particle degrees of freedom in nuclei in the framework of simple classical models. Order-of-magnitude estimates show that, without invoking the residual nucleon-nucleon interaction, the coupling of collective and single-particle motion is not strong enough to produce dynamical chaos in any of these models. (orig.)

[en] In an attempt to determine wether the low-lying parts of nuclear spectra are regular or chaotic, we analyse a recent set of data on low-lying levels in nuclei ranging from ²⁴Na to ²⁴⁴Am. We evaluate the nearest-neighbour spacing distribution and the Δ₃ statistic. We find strong indications for regularity in rotational-like states in even-even nuclei, and some evidence that natural parity states in odd-odd nuclei are not completely chaotic. The other states in both types of nuclei seem to have statistical distributions which are consistent with complete chaoticity. (orig.)