[en] We propose a new global α-nucleus optical model potential that takes into account the strong energy dependence and nuclear structure effects that characterize the alpha-nucleus interaction. The potential consists of a double-folded real part and a Woods-Saxon imaginary part with a Fermi-type energy dependence. The influence of purely volume absorption, volume plus surface absorption, as well as the dispersive relation is investigated. Three potentials are considered that are able to reproduce the bulk of existing experimental data at low energies. The need for more experimental data in the mass region A approx. = 100 and A approx. = 200 is stressed

[en] A method to identify all the S-matrix poles for a finite range potential is presented. The method is applied in the case of a square potential. A new class of resonant states is found and its properties are investigated. The study is extended to the Woods-Saxon and to the Woods-Saxon (square) well plus Coulomb barrier potentials.(authors)

[en] An outline of the theoretical treatment of the one-particle transfer reactions and of the spectroscopic information extracted from the study of these reactions is given. (author)

[en] There are different types of nuclear reactions which require different detection and identification methods. An outline of methods adequate for different situations is given. What has been achieved in this field is demonstrated by some experiments performed until now. (author)

[en] Many nuclear astrophysics applications involve radiative α-particle captures, α decays and α-particle transfer reactions. Theoretical estimates of the corresponding reaction rates within the framework of the statistical model of Hauser-Feshbach remain highly uncertain due to the poor knowledge of the α-nucleus optical model potential, especially at low energies far below the Coulomb barrier. In the present paper we propose a new global α-optical potential that takes into account the strong energy dependence and nuclear structure effects that characterize the α-nucleus interaction. The real part of the potential is calculated using a double-folding procedure over the M3Y effective nucleon-nucleon interaction. A Woods-Saxon potential is used for the imaginary potential where now a new parameterization is introduced to describe its energy dependence. The influence of purely volume absorption or volume plus surface absorption on the description of the experimental data is investigated. Finally, the dispersive relation is applied to relate the real and imaginary parts of the optical model potential and reduce the ambiguities in deriving the potential from experimental data. The three potentials considered are able to reproduce well the bulk of experimental data on (α,γ), (α, n), (α, p) and (n, α) reactions as well as the existing elastic scattering data at energies of relevance to astrophysical applications. However, when considering reaction rates on experimentally unexplored targets, deviations within a factor of 10 are found. These uncertainties are principally due to the difficulty in constraining the diffuseness of the imaginary potential from analyses of existing experimental data

[en] A global method to identify all the S-matrix poles k=k_l(g) in the k-plane for a central potential gV(r) (g element-of C) is presented. The method involves construction of the Riemann surface R_g^(l) over the g-plane, on which the function k = k_l(g) is single valued and analytic. It implies the division of the Riemann surface R_g^(l) into Σ_n^(l) sheets and the construction of the sheet images Σ_n^'(l) in the k-plane. The method is first applied to potentials having Jost entire functions in both variables g and k. In this case the general properties of the function k = k_l(g) and of its Riemann surface R_g^(l) are obtained. The method is then extended to other classes of potentials. The construction of the Riemann surface R_g^(l) as well as the construction of the images of its sheet in the k-plane for some particular potentials is given in detail. The method is allowed to identify new classes of resonant state poles. These poles remain in a neighborhood of some special points called open-quotes stable-pointsclose quotes as the strength of the potential increases to infinity; i.e., these resonant state poles do not become bound or virtual state poles. Moreover, the wave functions of the resonant states corresponding to the new-class poles situated in the neighborhood of the stable-points are almost completely localized outside the potential well. The method provides a quantum number has a topological significance: it is the label of the sheets of the Riemann surface R_g^(l). The existence of new classes of resonant state poles seems to be a general property of the potentials with barriers used in nuclear scattering theory. 35 refs., 14 figs., 2 tabs

[en] The conditions for the occurrence of a minimum of the compression factor with respect to the energy and to the potential parameters are studied. The excitation energies and the region of nuclei where pure threshold states of a given cluster could occur are determined. (authors)

[en] The focusing and dispersion of charged particles in magnetic fields, the construction and performances of some types of magnetic spectrographs are presented. Some examples of nuclear physics experiments using magnetic spectrographs are given. (author)

[en] A method to study from a global point of view all the resonant states is developed and applied for a square potential. New class of resonance states are identified by this method. The analysis is extended for the Woods-Saxon plus Coulomb barrier and for the square couple channels potentials. (authors)

No abstract available