RESUMEN
Plastic organic scintillators such as the blue-emitting BCF-12 are versatile and inexpensive tools. Recently, BCF-12 scintillators have been foreseen for investigation of the spatial distribution of neutrons emitted from dense magnetized plasma. For this purpose, small-area (5 mm × 5 mm) detectors based on BCF-12 scintillation rods and Hamamatsu photomultiplier tubes were designed and constructed at the Institute of Nuclear Physics. They will be located inside the neutron pinhole camera of the PF-24 plasma focus device. Two different geometrical layouts and approaches to the construction of the scintillation element were tested. The aim of this work was to determine the efficiency of the detectors. For this purpose, the experimental investigations using a neutron generator and a Pu-Be source were combined with Monte Carlo computations using the Geant4 code.
Asunto(s)
Cámaras gamma , Método de Montecarlo , Neutrones , Fibras Ópticas , Plásticos , Conteo por Cintilación/instrumentación , Simulación por Computador , Diseño de Equipo , Dosis de Radiación , Conteo por Cintilación/métodosRESUMEN
A method of tomographic reconstruction of the neutron emissivity in the poloidal cross section of the Joint European Torus (JET, Culham, UK) tokamak was developed. Due to very limited data set (two projection angles, 19 lines of sight only) provided by the neutron emission profile monitor (KN3 neutron camera), the reconstruction is an ill-posed inverse problem. The aim of this work consists in making a contribution to the development of reliable plasma tomography reconstruction methods that could be routinely used at JET tokamak. The proposed method is based on Phillips-Tikhonov regularization and incorporates a priori knowledge of the shape of normalized neutron emissivity profile. For the purpose of the optimal selection of the regularization parameters, the shape of normalized neutron emissivity profile is approximated by the shape of normalized electron density profile measured by LIDAR or high resolution Thomson scattering JET diagnostics. In contrast with some previously developed methods of ill-posed plasma tomography reconstruction problem, the developed algorithms do not include any post-processing of the obtained solution and the physical constrains on the solution are imposed during the regularization process. The accuracy of the method is at first evaluated by several tests with synthetic data based on various plasma neutron emissivity models (phantoms). Then, the method is applied to the neutron emissivity reconstruction for JET D plasma discharge #85100. It is demonstrated that this method shows good performance and reliability and it can be routinely used for plasma neutron emissivity reconstruction on JET.
Asunto(s)
Procesamiento de Imagen Asistido por Computador/métodos , Neutrones , Tomografía , Electrones , Gases em Plasma , Reproducibilidad de los Resultados , IncertidumbreRESUMEN
The thermal neutron diffusion parameters of a rock material depend on the rock matrix itself and on the water content. The effect has been studied in quartz by Monte Carlo (MC) simulations of the variable buckling experiment for nine series of samples. A hyperbolic dependence of the density-removed diffusion cooling coefficient on the water content shows a variability of this parameter by two orders of magnitude. The function obtained for wet quartz is compared with the analogous dependence for wet dolomite.
Asunto(s)
Simulación por Computador , Método de Montecarlo , Neutrones , Cuarzo/química , Agua/química , DifusiónRESUMEN
The water content in a rock material can significantly change the thermal neutron diffusion parameters with respect to those of the dry medium. The effect has been studied for dolomite, CaMg(CO3)2, by Monte Carlo simulations of the variable buckling experiments for 10 series of samples. The density-removed diffusion cooling coefficient C(M) varies hyperbolically by two orders of magnitude with water content in the range of 0-20%.
RESUMEN
The pulsed neutron experiment (the variable geometric buckling experiment) in spherical geometry has been simulated using the MCNP code. The time decay of the thermal neutron flux has been observed as a function of the sample size. The thermal neutron diffusion cooling coefficient C with the correction F has been determined for three basic rock minerals (quartz, calcite, dolomite) at the given specific densities. The corresponding density-removed parameters have also been obtained.
RESUMEN
The thermal neutron absorption cross section of a heterogeneous material is lower than that of the corresponding homogeneous one which contains the same components. When rock materials are investigated the sample usually contains grains which create heterogeneity. The heterogeneity effect depends on the mass contribution of highly and low-absorbing centers, on the ratio of their absorption cross sections, and on their sizes. An influence of the granulation of silicon and diabase samples on the absorption cross section measured with Czubek's method has been experimentally investigated. A 20% underestimation of the absorption cross section has been observed for diabase grains of sizes from 6.3 to 12.8 mm.