Search

The ultrasmall- and wide-angle neutron diffraction methods are used to study multiscale structures and phase transformations in synthetic opals at different temperatures and pressures (as high as 1500°C and 10 GPa, respectively). Monodisperse colloidal particles of amorphous silica dioxide ( a-SiO) with an average diameter of 150-1700 nm whose deviation from the mean is less than 5% are synthesized to fabricate the samples. Opal matrices up to 3 cm thick are obtained via the natural sedimentation of a SiO-globule suspension followed by drying and heat treatment. Neutron-diffraction processes are investigated using a DISK multidetector superposition diffractometer mounted at the IR-8 reactor of the National Research Centre Kurchatov Institute at a neutron wavelength of 1.668 Å. Ultrasmall-angle diffraction experiments are performed in the two-crystal mode of a STOIK spectrometer. [ABSTRACT FROM AUTHOR]

Filtered neutron techniques were applied to produce quasi-monoenergetic neutron beams in the energy range of 1.5–133 keV at research reactors. A simulation study was performed to characterize the filter components and transmitted beam lines. The filtered beams were characterized in terms of the optimal thickness of the main and additive components. The filtered neutron beams had high purity and intensity, with low contamination from the accompanying thermal emission, fast neutrons and γ-rays. A computer code named “QMNB” was developed in the “MATLAB” programming language to perform the required calculations. [ABSTRACT FROM AUTHOR]

Abstract: A computer package QMENF-G was developed in a general form to calculate the optimum amounts and components of quasi-mono-energetic neutron filters and their transmitted spectra in order to meet requirements for different applications in various fields. This code is a complete system to assist the user with input preparation, running calculations and analysis of output results. It is written in standard FORTRAN that runs on any personal computer using windows operating system. As a test case, the components and amounts of elements for producing a neutron filter at ∼3.8keV was calculated using QMENF-G code. It was found that 54Fe, 80Se or 90Zr, can be used as the main components of such filter. However, its transmission, resolution and purity were found to depend upon the accompanying components and their amounts. [Copyright &y& Elsevier]

Abstract: A formula is given which, for neutron energies in the range 10−4 < E <10eV, permits calculation of the nuclear capture, thermal diffuse and Bragg scattering cross-sections as a function of magnesium oxide (MgO) temperature and crystal parameters. Computer program has been developed to calculate the total neutron cross-section and transmission through mono-crystalline MgO. The calculated neutron transmission and effective attenuation coefficient values for MgO-single crystal at different temperatures are compared with measured ones. An overall agreement is indicated between the formula fits and experimental data. A feasibility study for the use of MgO-single crystal is discussed in terms of the optimum MgO-single crystal thickness, mosaic spread, temperature and cutting plane for efficient transmission of thermal-reactor neutrons, and also for rejection of the accompanying fast neutrons and gamma rays. Calculation shows that 10cm thick MgO-single crystal cut along its (100) plane, with 0.5° FWHM on mosaic spread and cooled at 77K, is a good thermal neutron filter, with high effect-to-noise ratio. [Copyright &y& Elsevier]

Abstract: Neutron filters/attenuators have been designed and constructed as an upgrade of the JET gamma-ray cameras (GRC''s). This diagnostics upgrade should reduce the neutron flux at the gamma-ray detectors in a way that it would make possible gamma-ray imaging measurements in high power deuterium JET pulses, and eventually in deuterium–tritium discharges. The attenuators will be placed within the GRC diagnostics system between the vacuum vessel port and the camera collimator radiation shields in the case of both the horizontal camera and the vertical one and they have to be moved out of the detector line of sight when the neutron/gamma camera diagnostics is used for neutron measurements. The neutron filters will operate in a very harsh electromagnetic environment. It is thus recommended to avoid as much as possible the use of electrical and electronic components for the attenuator steering and control (in particular, for attenuator steering). Therefore a steering and control system based on pneumatic components was designed and constructed. The attenuators together with the steering and control system have been installed on a test stand, which is a 1–1 scale replica of the JET structures where neutron filters are to be installed and successfully tested. [Copyright &y& Elsevier]