Suppression of soft nuclear bremsstrahlung in proton-nucleus collisions

Photon energy spectra up to the kinematic limit have been measured in 190 MeV proton reactions with light and heavy nuclei to investigate the influence of the multiple-scattering process on the photon production. Relative to the predictions of models based on a quasi-free production mechanism a strong suppression of bremsstrahlung is observed in the low-energy region of the photon spectrum. We attribute this effect to the interference of photon amplitudes due to multiple scattering of nucleons in the nuclear medium.Comment: 12 pages, 3 figures, submitted to Phys. Rev. Let

Use of Dirac-Coulomb Sturmians of the first order for relativistic calculations of two-photon bound-bound transition amplitudes in hydrogen-like ions

A fully relativistic treatment of the S-matrix elements describing two-photon bound - bound transition amplitudes in hydrogen-like ions is undertaken in the present work. Several selected transitions from the ground state vertical bar 1(2)S > towards the L and M shells (vertical bar 2(2)S >, vertical bar 3(2)S >, vertical bar 3(2)D(3/2)> and vertical bar 3(2)D(5/2)>) are described. For that purpose, we use the complete set of relativistic Sturmian functions derived by Szmytkowski ( 1997 J. Phys. B: At. Mol. Opt. Phys. 30 825) from the first-order Sturm-Liouville problems for the Dirac equation. The method followed consists of writing the matrix elements in terms of Green functions expanded over the first-order Dirac - Coulomb Sturmians. Previous approaches used a Sturmian basis associated with the Gell-Mann-Feynman equation. On the other hand, a distinctive feature of our tensor treatment is that the expressions derived are quite general and could be applied to any multipole of the two-photon bound - bound transitions. In the case of dipole transitions, considered also by Szymanowski et al ( 1997 Phys. Rev. A 56 700) in their calculations, the selection rules derived from our method lead to two additional terms related to l(1p) = 2 and l(2p) = 2. The numerical results obtained for the transition from the ground state vertical bar 1(2)S > towards the L and M shells enable us to draw inferences as to the improvements of our method

Natural radiation exposure to the public in the oil-bearing Bakassi Peninsula, Cameroon

The objective of the present study was to carry out natural radioactivity measurements and corresponding dose assessment in the Bakassi Peninsula, an oil-bearing area located in the Gulf of Guinea. This pilot study required E-perm Electret Ionization Chamber (EIC) exposure in homes and the sampling of soils and foodstuffs representative of the food consumption patterns of the population of Bakassi. The results show high exposure of members of the public to natural radiation. Elevated indoor radon concentrations due to building construction were observed, and high exposure to 210Po attributable to the dietary habits of the local population, mainly consisting of seafood. Finally, a total dose of 34.6 mSv.y-1 was found, much higher than the world average value. In the case of confirmation of the results of this study, countermeasures must be taken into consideration to avoid such a high level of exposure, to reduce the radiation dose to the population. Taking into account the limited number of samples, the present work should be considered as a preliminary study

Expectation values of rqr^{q} between Dirac and quasirelativistic wave functions in the quantum-defect approximation

A search is conducted for the determination of expectation values of $r^q$ between Dirac and quasirelativistic radial wave functions in the quantum-defect approximation. The phenomenological and supersymmetry-inspired quantum-defect models which have proven so far to yield accurate results are used. The recursive structure of formulae derived on the basis of the hypervirial theorem enables us to develop explicit relations for arbitrary values of $q$. Detailed numerical calculations concerning alkali-metal-like ions of the Li-, Na- and Cu-iso electronic sequences confirm the superiority of supersymmetry-based quantum-defect theory over quantum-defect orbital and exact orbital quantum number approximations. It is also shown that relativistic rather than quasirelativistic treatment may be used for consistent inclusion of relativistic effects

Hypervirial and Hellmann-Feynman theorems applied to the calculation of energy levels for relativistic particles

The nonrelativistic hypervirial Hellmann-Feynman method developed recently is extended to deal with relativistic particles bound in a spherically symmetric potential. A simple analytical procedure for calculating correction terms of arbitrary high orders is derived. Numerical results obtained through a study of the screened Coulomb potential enable us to illustrate the improvements of our procedure over the previous approaches

Effects of the electron's anomaly in relativistic laser-assisted Mott scattering

We investigate the influence of the electron's anomalous magnetic moment on the process of relativistic Mott scattering in a powerful electromagnetic plane wave for which the ponderomotive energy is of the order of the magnitude of the electron's rest mass. For this purpose, we use the Coulomb - Dirac - Volkov and the Dirac - Volkov functions with the electron's anomaly to describe the initial and final states respectively. First- order Born differential cross-sections of induced and inverse bremsstrahlung are obtained for linearly polarized laser light. Numerical calculations are carried out for various parameters values (i.e. scattering angle, the nucleus charge, photon energy, electrical field) and are compared with results obtained by Li et al 2004 ( J. Phys. B: At. Mol. Opt. Phys. 37 653). It is found that for parameters used in the present work, incorporating the anomaly of the electron in the initial and final states yields cross-sections which are strongly modified whatever the scattering geometry as compared to the outcome of the previous treatment