We point out a misleading treatment in the recent literature regarding analytical solutions for nonminimal vector interaction for spin-one particles in the context of the Duffin-Kemmer-Petiau (DKP) formalism. In those papers, the authors use improperly the nonminimal vector interaction endangering in their main conclusions. We present a few properties of the nonminimal vector interactions and also present the correct equations to this problem. We show that the solution can be easily found by solving Schrödinger-like equations. As an application of this procedure, we consider spin-one particles in presence of a nonminimal vector linear potential.
The problem of spin-0 particles subject to a nonminimal vector double-step potential is explored in the context of the Duffin-Kemmer-Petiau theory. Surprisingly, one can never have an incident wave totally reflected and the transmission amplitude has complex poles corresponding to bound states. The interesting special case of bosons embedded in a sign potential with its unique bound-state solution is analyzed as a limiting case.
A growing community of scientists has been using neutrons in the most diverse areas of science. In order to meet the researchers demand in the areas of physics, chemistry, materials sciences, engineering, cultural heritage, biology and earth sciences, the Brazilian Multipurpose Reactor (RMB) will provide 3 thermal guides and 3 cold guides, with the installation of several instruments for materials characterization. In this study, we present a standard design requirement of two primordial instruments, namely Sabiá and Araponga. They are, respectively, cold and thermal neutron instruments and correspond to a Small-Angle Neutron Scattering (SANS) and High-Resolution Powder Neutron Diffractometer (HRPND) to be installed in the Neutron Guide Building (N02) of RMB. To provide adequate flux for both instruments, we propose here an initial investigation of the use of simple and split guides to transport neutron beams to two different instruments on the same guide. For this purpose, we use Monte Carlo simulations utilizing McStas software to check the efficiency of thermal neutron transport for different basic configuration and sources. By considering these results, it is possible to conclude that the split guide configuration is, in most cases, more efficient than cases that use transmitted neutron beams independently of source. We also verify that the employment of different coating indexes for concave and convex surfaces on curved guides is crucial, at least on simulated cases, to optimise neutron flux (intensity and divergence) and diminish facility installation cost. References 21As a multipurpose reactor, the RMB project also contains applications in neutron research and instruments. The neutron applications of the RMB project are the irradiation process, which occurs inside the reflector tank, and measurement process, which takes place at the N02 building (number 14 in Figure 1) and is often complementary to synchrotron radiation investigations. According to the basic project, there will be available in-core positions for materials irradiation tests and positions inside reflector for applying the neutron activation analysis (NAA) technique, which possesses numerous applications, e.g., in geology, archaeology, biology, medicine, environment, industry, chemistry, nutrition, and agriculture.Concerning applications inside N02, the detailed project of RMB contains, according to the main current research reactors, a series of state-of-art instruments that still have to be properly defined. In this study, we present two priority neutron scattering instruments that compose the detailed project of the RMB neutron guide hall (N02), namely Small-Angle Neutron Scattering (SANS) and the High-Resolution Powder Neutron Diffractometer (HRPND).SANS is a flexible and disseminated technique for studying object structures on the nanoscale. Besides its unique property in investigating magnetic material, not contemplated by traditional SAXS technique (Small Angle X-Ray Scattering). SANS is used in looking to polymer and biological molec...
A: Neutron transport along guides is governed by the Liouville theorem and the technology involved has advanced in recent decades. Computer simulations have proven to be useful tools in the design and conception of neutron guide systems in facilities. In this study, we use a Monte Carlo method to perform simulations for an S-shaped neutron guide with different dimensions for a Small-Angle Neutron Scattering (SANS) instrument, through the MCSTAS software. A wavelength cutoff is observed and shown to be dependent on the geometrical parameters of the guide. Results for the neutron flux at sample position are presented and a greater sensitivity of cutoffs concerning the curvatures of the guides than to their lengths is noticed. Our results are in agreement with those obtained from the Acceptance Diagram method and we analyze the beam divergence behavior along the S-shaped guide. K: Instrumentation for neutron sources, Neutron sources, Instrument optimization, Simulation methods and programs.
The general Dirac equation in 1+1 dimensions with a potential with a completely general Lorentz structure is studied. Considering mixed vector-scalar-pseudoscalar square potentials, the states of relativistic fermions are investigated. This relativistic problem can be mapped into a effective Schrödinger equation for a square potential with repulsive and attractive delta-functions situated at the borders. An oscillatory transmission coefficient is found and resonant state energies are obtained. In a special case, the same bound energy spectrum for spinless particles is obtained, confirming the predictions of literature. We showed that existence of bound-state solutions are conditioned by the intensity of the pseudoscalar potential, which posses a critical value.
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