Effect of electromagnetic fields on the creation of scalar particles in a flat Robertson-Walker space-time

The influence of electromagnetic fields on the creation of scalar particles from vacuum in a flat Robertson-Walker space-time is studied. The Klein Gordon equation with varying electric field and constant magnetic one is solved. The Bogoliubov transformation method is applied to calculate the pair creation probability and the number density of created particles. It is shown that the electric field amplifies the creation of scalar particles while the magnetic field minimizes it.Comment: Important modifications, 20 pages, To appear in Eurpean Physical Journal C. arXiv admin note: text overlap with arXiv:1108.033

Any l-state improved quasi-exact analytical solutions of the spatially dependent mass Klein-Gordon equation for the scalar and vector Hulthen potentials

We present a new approximation scheme for the centrifugal term to obtain a quasi-exact analytical bound state solutions within the framework of the position-dependent effective mass radial Klein-Gordon equation with the scalar and vector Hulth\'{e}n potentials in any arbitrary $D$ dimension and orbital angular momentum quantum numbers $l.$ The Nikiforov-Uvarov (NU) method is used in the calculations. The relativistic real energy levels and corresponding eigenfunctions for the bound states with different screening parameters have been given in a closed form. It is found that the solutions in the case of constant mass and in the case of s-wave ($l=0$) are identical with the ones obtained in literature.Comment: 25 pages, 1 figur

Étude et réalisation d'un spectromètre « y » multimode

Nous avons étudié et réalisé un spectromètre « γ » multimode, qui permet la détection séparée et simultanée des photons suivant les trois modes : absorption totale, effet photoélectrique et anti-Compton, effet de paires. Il se compose d'un détecteur central Ge(Li) et d'un cristal annulaire INa de gros volume formé de quatre secteurs optiquement isolés

Étude et réalisation d'un spectromètre « y » multimode

We have studied and designed a "multimode" gamma ray spectrometer, which permits the separate and simultaneous detection of photons according to three mcdes : total absorption photoelectric and anti-Compton effects, pair effect. The spectrometer consists of a central Ge(Li) detector and of a large INa annulus split in four optically separated sectors.Nous avons étudié et réalisé un spectromètre « γ » multimode, qui permet la détection séparée et simultanée des photons suivant les trois modes : absorption totale, effet photoélectrique et anti-Compton, effet de paires. Il se compose d'un détecteur central Ge(Li) et d'un cristal annulaire INa de gros volume formé de quatre secteurs optiquement isolés

ETUDE DES REACTIONS 11B (n, X γ)

Nous avons étudié la distribution angulaire des photons émis par la réaction 11B (n, n' γ), pour des énergies de neutrons de 7,18 MeV, 8,5 MeV et 9,72 MeV, la première et la dernière énergie correspondant à des résonances du Noyau Composé. La fonction d'excitation à 90° de ces mêmes photons a été mesurée pour la gamme d'énergie 4,8 MeV - 9,7 MeV.We have studied the angular distribution of photons following the 11B (n, n') 11B* reaction, at neutron energies of 7,18 MeV, 8,5 MeV and 9,72 MeV ; the first and the third energies correspond to compound nucleus resonance. The excitation fonction at 90° of these photons, has been measered in the 4,8 - 9,7 MeV energy range

Challenging microscopic structure and reaction models for nucleon scattering off nuclei in the A=208 mass region

International audienceWe present a microscopic description of neutron and proton elastic and inelastic scattering off Pb206,207,208 and Bi209 together with new medium-energy (7.5–15.5 MeV) neutron elastic and inelastic scattering measurements for various low-energy levels. The Jeukenne, Lejeune, Mahaux (JLM) semimicroscopic folding model provides the relevant optical and transition potentials used to calculate the elastic and inelastic cross sections. Rearrangement corrections that account for proton and neutron density variations during the transition are considered. The nuclear diagonal and transition densities are calculated from a (quasiparticle) random phase approximation [(Q)RPA] structure model implemented with the Gogny D1S interaction. Calculated differential elastic and inelastic cross sections are mostly in very good agreement with available data. Predicted nuclear structure properties as well as scattering calculations and measurements for the yrast quadrupole excitation in Pb206 are carefully discussed. The rearrangement corrections to inelastic scattering form factors are shown to reduce medium energy nucleon inelastic cross section by up to 55%. The magnitude of these corrections changes depending on the probe, incident energy, multipolarity, and nature of the transitions considered. The combined analysis of nuclear structure properties and those for nucleon scattering cross sections measured previously over a range of incident energies provides stringent tests of present microscopic models and helps distinguish those scattering data which most likely call for revision