[en] The crystallite sizes of simulated DUPIC fuel powders were measured by the neutron diffraction line broadening method. The amount of fission products in spent fuels was calculated by the ORIGEN-2 code and the oxides of stable isotopes were added into natural uranium oxide. The mixed UO₂ and fission product oxides powders were dry-milled in an attritor with a rotation speed of 200rpm, ball-to-powder ratio of 4:1 for 30, 60, and 120 minutes. The simulated DUPIC fuel powders were compacted into pellets under a pressure of 3 ton/cm² and 4 pellets were stacked in a vanadium can for neutron diffractometry by the HRPD in HANARO. The wavelength of neutron beam was 1.8348, and the monochrometer was Ge(331) single crystal. The diffraction patterns were obtained from 20 to 155 .deg. by 2θ interval of 0.05 .deg., and the maximum intensity was about 20000 cps. Fullprof 1.9c code was used for the Rietveld refinement and the full-width-at-half-maximum (FWHM) was obtained. A more reliable result of crystallite size was obtained by Cauchy-Gaussian convolution method using the FWHM from fitting of each diffraction profile. The most reliable result was the fitting by the Voigt function and Warren-Averbach deconvolution method

[en] The characteristics of a neutron diffractometer using a ³He one-dimensional position-sensitive detector (PSD) with delay line readout, a 200 (length) x 100 (height) mm² active window and 2.5 mm spatial resolution have been studied and compared with those of the High-Resolution Powder Diffractometer (HRPD) of KAERI with 32 ³He conventional tube (diameter 50 mm) detectors and Soller collimators (10') before detectors. For the sample to PSD distance R=1200 mm, the PSD subtends 8 deg. angle of 2θ and provides the resolution and the peak-to-background ratio close to that for HRPD. Time for scanning (with the same statistics) of a 0-160 deg. interval is about 1.6 times longer and the multi-PSD system providing efficiency about 10 times higher than HRPD is proposed. Because of the small angle subtended by the PSD, the parasitic peaks from the sample environment are eliminated and operation without an oscillating radial collimator is possible. Additionally, the proposed diffractometer has an advantage for small samples

[en] The static property of an Ising-like quasi one dimensional antiferromagnets are studied by using the neutron scattering measurements based on the background of theoretical calculations. We have found the magnetic three dimensional transition temperatures with an addition of magnetic impurities drastically decreases for the polycrystalline sample. The study of the critical phenomena near the transition temperature has not been possible in this measurements caused by the lack of large scattering intensities. This work, though, open the possibility of further studies in this system with single crystals. This work also enables us to have confidence in magnetic studies for other systems

[en] The structural, magnetic, and transport properties of a mono-layered manganite La_0.7Sr_1.3MnO_4+δ were investigated using variable temperature neutron powder diffraction as well as magnetization and transport measurements. The compound adopts the tetragonal I4/mmm symmetry and exhibits no magnetic reflection in the temperature region of 10 K ≤ T ≤ 300 K. A weak ferromagnetic (FM) transition occurs about 130 K, which almost coincides with the onset of a metal-insulator (M-I) transition. Extra oxygen that occupies the interstitial site between the ((La,Sr)O) layers makes the spacing between the (MnO₂) layers shorten, which enhances the inter-layer coupling and eventually leads to the M-I transition. We also found negative magneto resistance (MR) below the M-I transition temperature, which can be understood on the basis of the percolative transport via FM metallic domains in the antiferromagnetic (AFM) insulating matrix

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[en] The lattice parameters of simulated DUPIC fuel and UO2 were measured from room temperature to 1273 K using neutron diffraction to investigate the thermal expansion and density variation with temperature. The lattice parameter of simulated DUPIC fuel is lower than that of UO2 and the linear thermal expansion of simulated DUPIC fuel is higher than that of UO2. For the temperature range from 298 to 1273 K, the average linear thermal expansion coefficients for UO2 and simulated DUPIC fuel are 10.471 ''10-6 and 10.751 ''10-6 K-1, respectively

[en] The purpose of this paper was to investigate the effect of photon flux on the recorded energy spectrum and images produced with a photon-counting detector. We used a photon-counting cadmium telluride (CdTe) x-ray detector (model PID350, Oy Ajat, Finland). The CdTe array was composed of 16 384 pixels, each 0.35 × 0.35 × 0.75 mm³ in dimension. The photon flux is controlled by an additional aluminum filter (1, 10, 20, 30 and 40 mm). Images were acquired at three different tube voltages (50, 70 and 90 kVp) with various thicknesses of photon flux control (PFC) filters. The data acquisition time was changed to acquire an approximately equal number of counts within the selected energy window between different thicknesses of PFC filters at the same tube voltage. A phantom was manufactured to evaluate the photon flux effect on the image. The phantom was made from polymethyl methacrylate and four concentrations of iodine. The photon flux effect on the image was evaluated by the signal-difference-to-noise ratio (SDNR) between iodine and the background material. The changes of photon flux affected the recorded energy spectra and image. The thickness of the PFC filter that showed the maximum SDNR differed according to the tube voltage. The 10 mm PFC filter showed the highest SDNR at 50 and 70 kVp, while the 30 mm PFC filter exhibited the highest SDNR at 90 kVp. The SDNR was improved up to, on average, 30-fold in optimal photon flux conditions which acquired a spectrum including the lowest electronic noise with no pulse pile-up effect. The results of this study showed that the photon flux affected not only the acquired energy spectrum but also the image. Based on these results, the spectral distortion correction should be considered in connection with the image that is the ultimate purpose of medical imaging. (paper)

[en] Recently, there has been an increase in the demand for semiconductor detectors in the field of nuclear medicine imaging. The development of semiconductor detectors using materials such as CdTe that allowed for improved spatial resolution greatly advanced the field. However, the pinhole collimator that allows for high spatial resolution compromises the sensitivity due to the small size of the hole. An improvement in both sensitivity and spatial resolution may be achieved by using a pixelated parallel-hole collimator where the hole and pixel sizes are the same. The purpose of this study was to optimize the design of a detector and collimator system to achieve excellent resolution and high sensitivity for a SPECT detector based on a CdTe detector. We performed a simulation study of the PID 350 (Ajat Oy Ltd., Finland) CdTe detector by using a Geant4 Application for Tomographic Emission (GATE). In addition to the above-mentioned pixelated parallel-hole collimator, we also designed a hexagonal parallel-hole collimator with similar hole size, and we evaluated the sensitivity and spatial resolution of each to determine which set-up was optimal for the PID 350 CdTe detector. Our results indicated that the average sensitivity and spatial resolution were 33.48% and 10.97% higher for the pixelated parallel-hole collimator than for the hexagonal parallel-hole collimator, respectively. We resolved a diameter of 0.5 mm in hot-rod phantom images with the pixelated parallel-hole collimator at a distance of 2 cm. Based on our results, we recommend the pixelated parallel-hole collimator for improving the sensitivity and spatial resolution of SPECT systems with CdTe semiconductor detectors.

[en] Spontaneous and magnetic field induced incommensurate – commensurate magnetic phase transitions have been studied in Tb_1-xEr_xNi₅ compounds near the critical concentration x _c = 0.125. Compounds crystallize in the hexagonal CaCu₅ type phase (P6/mmm space group). In compounds with x ≥ x _c the magnetic order is a commensurate ferromagnetic one. The samples with x < x _c have an incommensurate structure that is a fan like magnetic structure and described by two propagation vectors. An incommensurate – “lock in” magnetic transition takes place at 10 K at cooling regime. (paper)