Physics Procedia最新文献

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.

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.

The radiocarbon concentration is reduced in urban areas, generally due to high CO₂ emissions derived from fossil fuels. In this paper, new Δ¹⁴C measurements in cellulose extracted from the growth rings of two trees over a 43-year period are presented. The first is in a zone with clean air (El Nayar, Durango, Mexico) and the second is from the Greater Mexico City area (Chapultepec). Data from El Nayar is consistent with that reported for Zone 2 of the Northern Hemisphere while that from the urban area shows a significant decrease in Δ¹⁴C. Our results are compared with data from other cities (Nagoya, Japan and Valladolid, Spain).

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.

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.

For the neutron phase imaging with a Talbot-Lau interferometer, we have fabricated neutron absorption gratings with a pitch of 9 μm by oblique evaporation of gadolinium. The performances of these gratings for the phase measurement were experimentally evaluated at RADEN in J-PARC, by observing the neutron transmission and the visibility of moiré fringe in the interferometer. A new analysis method using the wavelength-resolved neutron transmission was also attempted to estimate the characteristics of gratings.

The Colorado School of Mines installed a neutron radiography system at the United States Geological Survey TRIGA reactor in 2012. An upgraded beamline could dramatically improve the imaging capabilities of this system. This project performed computational analyses to support the design of a new beamline, with the major goals of minimizing beam divergence and maximizing beam intensity. The new beamline will consist of a square aluminum tube with an 11.43 cm (4.5 in) inner side length and 0.635 cm (0.25 in) thick walls. It is the same length as the original beam tube (8.53 m) and is composed of 1.22 m (4 ft) and 1.52 m (5 ft) flanged sections which bolt together. The bottom 1.22 m of the beamline is a cylindrical aluminum pre-collimator which is 0.635 cm (0.25 in) thick, with an inner diameter of 5.08 cm (2 in). Based on Monte Carlo model results, when a pre-collimator is present, the use of a neutron absorbing liner on the inside surface of the beam tube has almost no effect on the angular distribution of the neutron current at the collimator exit. The use of a pre-collimator may result in a non-uniform flux profile at the image plane; however, as long as the collimator is at least three times longer than the pre-collimator, the flux distortion is acceptably low.

Spectroscopic neutron Bragg-edge imaging was performed to study a lithium-ion battery (LIB) product. This non-destructive neutron imaging method is suitable for the evaluation of industrial products, but presents some difficulties for application to multicomponent products. The LIB includes a strong neutron scatterer and an absorber, and is thus a suitable test case for the use of neutron imaging in actual product measurement. In this study, we analyzed the variation of the graphite anode structure with changes in the battery charge level. The experiments were carried out using the compact neutron source at the Hokkaido University neutron source facility (HUNS). To eliminate the effect of scattered neutron contamination, we first determined the distance between the sample and detector required to reduce this effect to under 1%. Using this separation, the charge level dependence of the anode structure was measured. The graphite {002} Bragg-edge could be recognized on the neutron transmission spectra. The Bragg-edge was shifted and broadened with increasing battery charge. The edge was consistent with the existence of multiple graphite structural stages. The layer spacing distribution images for different charge levels showed the inhomogeneous fluctuation on the LIB lattice plane. Based on the images the fraction of the graphite structural stages were analyzed. The ratio of each stage varied with the charge level, and the ideal intercalation structure, in which the graphite layers are stuffed with Li-ions, was found to be minor in the final charging state.