Physics Procedia最新文献

In the search for a suitable detector for demonstration neutron radiography measurements on the zero-power VR-1 training reactor at the Czech Technical University in Prague, some options were considered. Due to the reactor's low power and spatial limitations, an easy and practical solution had to be found. Self-developing films represent a flexible detection tool in x-ray imaging. Therefore, the goal of this study was to evaluate their potential for neutron detection. For this purpose, bare and converter covered films were studied in the thermal and epithermal neutron beams at the LVR-15 research reactor in Rez, Czech Republic.

The experimental results show the sharply strengthened effects of acoustic emission from a breakdown zone by the joint influence of laser and ultrasonic irradiation. Various breakdown thresholds and character of acoustic emission in fresh and sea water are observed. The experimental result established that acoustic emission from optical breakdown of sea water in the presence and absence of ultrasound exceeds acoustic emission for the same experimental conditions in fresh water.

Line broadening analysis was performed on the time-of-flight neutron diffraction data for the plastically bent plates of a ferritic steel and a duplex stainless steel. A Rietveld analysis program, Z-Rietveld ver. 1.0 was used to fit the anisotropically broadened patterns where the increase in Lorentzian full width at half maximum (FWHM) and the Gaussian FWHM involves information of the crystallite size and the dislocation density, respectively. The derived results were compared with those obtained by using Bragg-edge transmission spectrum analysis and electron backscatter diffraction (EBSD) observations.

A new facility, named CERN-MEDICIS, is under construction at CERN to produce radionuclides for medical applications. In parallel, the MEDICIS-PROMED, a Marie Sklodowska-Curie innovative training network of the Horizon 2020 European Commission‘s program, is being coordinated by CERN to train young scientists on the production and use of innovative radionuclides and develop a network of experts within Europe. One program within MEDICIS-PROMED is to determine the feasibility of producing innovative radioisotopes for theranostics using a commercial middle-sized high-current cyclotron and the mass separation technology developed at CERN-MEDICIS. This will allow the production of high specific activity radioisotopes not achievable with the common post-processing by chemical separation. Radioisotopes of scandium, copper, arsenic and terbium have been identified. Preliminary studies of activation yield and irradiation parameters optimization for the production of Tb-149 will be described.

We have performed neutron radiography and tomography using a CCD camera-type detector for some test samples at RADEN. The current spatial resolution for neutron radiography is estimated to about 350 μm in the largest field-of-view of 300 × 300 mm² and 100 μm in the field-of-view of 60 × 60 mm². It is thought that the latter spatial resolution is strongly affected by the image blur in the scintillator screen. In the case of neutron tomography, the current spatial resolution is estimated to be better than 0.5 mm using an iron and aluminum test sample. Furthermore, we have performed neutron tomography for a cast aluminum product. As a result, small blowholes are found in the center of the product. This demonstrates the importance of non-destructive testing by neutron radiography and tomography for industrial products.

In a current laser welding production process of components of stainless steel, a butt joint configuration may lead to failures in the form of blowouts, causing an unacceptable welding quality. A study to improve the laser welding process was performed with the aim of solving the problem by designing a suitable pattern of multiple small laser spots rather than a single spot in the process zone.

The blowouts in the process are provoked by introducing small amounts of zinc powder in the butt joint. When the laser heats up the zinc, this rapidly evaporates and expands, leaving the melt pool to be blown away locally. Multiple spot pattern designs are tested. Spot patterns are produced by applying diffractive optics to a beam from a single mode fiber laser.

Results from welding while applying spot patterns both with and without trailing spots are presented. Data showing the power ratio between a trailing spot and two main spots as a function of spot distance is also presented.

The results of the study show that applying multiple spots in the welding process may improve the process stability when welding materials with small impurities in the form of zinc particles.

For neutron tomography, reconstruction accuracy greatly relies on exact registration of the projection and the back-projection coordinate system. Since the manufacturing and installing errors of mechanical components make the rotation axis projected in CCD camera deflect a certain angle, a mismatch between the projection coordinate and the detector coordinate will be caused consequently, resulting in obvious artifacts on the reconstructed images. In this paper, a calibration and correction method of the deflection angle of rotation axis projection is proposed to eliminate artifacts on neutron tomography images. First, all the projections among 360° rotation range are superposed together to create an averaged image with a unique symmetry axis. Then by segmentation and principal component analysis on the averaged image, the deflection angle is figured out. The calibrated angle is introduced to the reconstruction algorithm as an extra correction parameter, and artifacts-free images are finally obtained.

In this work the theoretical model of holographic formation of controllable waveguide channels system in photopolymer-liquid crystalline composition is developed. The ability to control the light propagation conditions in waveguides by external electric field impact is demonstrated.