Nuclear reactions in the uppermost Earth atmosphere as a source of the magnetospheric positron radiation belt

A physical mechanism for the formation of a natural positron belt in the Earth's magnetosphere is considered. It is assumed that a natural source of energetic positrons as well as electrons can be created owing to the decay of charged pions pi (+/-) --> mu (+/-) --> e(+/-), which have their origin in nuclear collisions between energetic trapped inner zone protons and heavier atoms (He and O) in the upper atmosphere of the Earth. Simulations of these processes demonstrate that there is a predominant production of positive pions over negative pions, and consequently the decays result in a substantial excess of positrons over electrons at energies greater than tens of MeV. This positron excess is found to be energy-dependent and to decrease with increasing incident proton energy; this excess is essentially absent at proton energies corresponding to cosmic ray primaries of greater than or equal to8 GeV. Our numerical computations for the resulting e(+)/e(-) fluxes provide ratio values of similar to4 at multi-MeV energies and at L = 1.2 +/- 0.1. The simulation results presented herein are compared to the existing and recent experimental evidence.O TEXTO COMPLETO DESTE ARTIGO, ESTARÁ DISPONÍVEL À PARTIR DE FEVEREIRO DE 2015.106A11261112611

On positron radiation belt in the Earth's magnetosphere

The ratio of positron/electron fluxes originated in nuclear spallation reactions in the Earth's magnetosphere is considered. It is supposed that positrons as well as electrons are produced in the decay of charged pions (pi(+/-) --> mu(+/-) --> e(+/-)) born in nuclear collisions of trapped relativistic inner zone protons with the residual atmosphere. These positrons and electrons are captured in the magnetosphere and create positron and electron radiation belts of nuclear origin. The positron/electron trapped magnetospheric fluxes formed with this mechanism are simulated and the resulting computed e(+)/e(-) flux ratio approximate to 4 appears in agreement with the recent observations. This ratio is significantly different from the ratio approximate to 1 obtained from the primary cosmic ray source through the same mechanism.30359059

Effect of Carbamide Peroxide on the Push-out Bond Strength of Different Composition Glass-Ionomer Cement to Root Canal Dentin when used as Cervical Barrier

Aim: To evaluate the effect of 37% carbamide peroxide on the bond strength of conventional or resin-modified glass-ionomer cements when used as a cervical barrier in endodonticallytreated teeth. Materials and methods: After root canal instrumentation and obturation, 40 specimens of the cement-enamel junction were obtained after transversal root canal sectioning from human extracted canines. The root canal specimens were standardized and filled with the following materials (n = 10, each group): G1: zinc phosphate (control), G2: Ketac glass-ionomer, G3: vitrebond glass-ionomer or G4: GC GL glass-ionomer. After 24 hours, the specimens were subjected to an application of 37% carbamide peroxide for 21 days, changed each 7 days and stored in an artificial pulp chamber. The specimens were then submitted to push-out bond strength testing with an electromechanical test machine (EMIC) and the failure mode in each specimen was analyzed with confocal microscopy (LEXT). Results: G3 and G4 showed higher bond strengths values than the other groups (p 0.05). G1 showed the lowest bond strength value (p < 0.05). Conclusion: Glass-ionomer cements showed higher bond strength values than the zinc phosphate cement, and resinmodified glass-ionomer cements presented the highest push-out values to root canal dentin (GC, GL and Vitrebond).Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Department of Postgraduate Program in Dentistry School of Dentistry CEUMA UniversityDepartment of Restorative Dentistry School of Dentistry Univ Estadual PaulistaDepartment of Dentistry School of Dentistry Univ Estadual PaulistaDepartment of Postgraduate Program in Integrated Dental Science School of Dentistry University of Cuiabá-UNICDepartment of Restorative Dentistry School of Dentistry Univ Estadual PaulistaDepartment of Dentistry School of Dentistry Univ Estadual Paulist