Collision of a Positron with the Capture of an Electron from Lithium and the Effect of a Magnetic Field on the Particles Balance

The processes of scattering slow positrons with the possible formation of positronium play an important role in the diagnosis of both composite materials, including semiconductor materials, and for the analysis of images obtained by positron tomography of living tissues. In this paper, we consider the processes of scattering positrons with the capture of an electron and the formation of positronium. When calculating the cross-section for the capture reaction, exchange effects caused by the rearrangement of electrons between colliding particles are taken into account. Comparison of the results of calculating the cross-section with a similar problem of electron capture by a proton showed that the mass effect is important in such a collision process. The loss of an electron by a lithium atom is more effective when it collides with a positron than with a proton or alpha particles. The dynamic equilibrium of the formation of positronium in the presence of a strong magnetic field is considered. It is shown that a strong magnetic field during tomography investigation shifts the dynamic equilibrium to the positronium concentration followed by positron annihilation with radiation of three gamma-quants.

Soil geochemistry of the municipality necropolis of Mata, RS, by fluorescence of x-rays by dispersive energy

The objective of this study was to detect the environmental impacts generated by the municipal Mata cemetery. In order to aid in the detection and monitoring of the area were used granulometric and chemical terms through EDXRF the study of soil. Considering the results obtained it is concluded that the soil analytical results showed presence of metals in all analyzes, but with levels below the maximum permitted values of metals in Brazilian soils. The Cd was an exception, for this metal values above 0.6 mg kg-1 were found. The clay/silt ratio less than 1.5 in the investigated samples indicates a more weathered soil on the surface than at depths of 30 cm in the cemetery area. Statistical data estimate highly significant Mg, Cl, Al, Fe, K, Ti and Rh factor loads on the surface and at depths, K, Ca, Cl, Al and Mg are the most important. The main ion exchanges correlate with the correlation coefficients found within the same order. Therefore, it is possible that the simultaneous increase or decrease in the cations is the result, mainly, of ionic exchange effects in the mineral assembly of the sediments investigated.

Counterintuitive effects of isotopic doping on the phase diagram of H2–HD–D2molecular alloy

Molecular hydrogen forms the archetypical quantum solid. Its quantum nature is revealed by behavior which is classically impossible and by very strong isotope effects. Isotope effects betweenH2,D2, and HD molecules come from mass difference and the different quantum exchange effects: fermionicH2molecules have antisymmetric wavefunctions, while bosonicD2molecules have symmetric wavefunctions, and HD molecules have no exchange symmetry. To investigate how the phase diagram depends on quantum-nuclear effects, we use high-pressure and low-temperature in situ Raman spectroscopy to map out the phase diagrams ofH2–HD–D2with various isotope concentrations over a wide pressure–temperature (P-T) range. We find that mixtures ofH2, HD, andD2behave as an isotopic molecular alloy (ideal solution) and exhibit symmetry-breaking phase transitions between phases I and II and phase III. Surprisingly, all transitions occur at higher pressures for the alloys than either pureH2orD2. This runs counter to any quantum effects based on isotope mass but can be explained by quantum trapping of high-kinetic energy states by the exchange interaction.