[en] Cosmic-ray muon radiography which has good penetrability and sensitivity to high-Z materials is an effective way for detecting shielded nuclear materials. The cosmic-ray muon imaging is designed to detect nuclear materials by taking advantage of natural cosmic-ray produced muons. The principle of the technique, its advantages in nuclear detecting field and main algorithm being used have been reviewed. At last we introduce some development of cosmic-ray muon imaging these years and prospect the application in detection of nuclear materials. (authors)

[en] Cosmic-ray muon radiography which has good penetrability and sensitivity to high-Z materials is an effective way for detecting shielded nuclear materials. The cosmic-ray muon imaging is designed to detect nuclear materials by taking advantage of natural, cosmic-ray produced muons. The principle of the technique, its advantages in nuclear detecting field and main algorithm being used have been reviewed. At last we introduce some development of cosmic-ray muon imaging these years and prospect the application in detection of nuclear materials. (authors)

[en] In muon tomography based on multiple Coulomb scattering, the scattering properties of cosmic-ray muons are distinctive even for the same target due to their different momentum distribution, which, to some extent, cast down the imaging resolution. For the purpose of suppressing or eliminating this effect, a multi-group model (MGM) of the momentum spectra of cosmic-ray muons was set up and validated by measuring the thicknesses of Pb slabs and by identifying the materials of unknown slabs. The results show that MGM can give a precise calculation of Pb slab thickness in the range of 1-16 cm, within an error of 5%. Moreover, MGM can also identify the materials of slabs by calculating the corresponding radiation lengths, which is especially effective for high-Z materials with an calculation error below 4%. (authors)

[en] Background: Due to the effect of near-field artifacts, the clearity of reconstructed image obtained by coded aperture imaging was decreased. Purpose: In order to explore a way to eliminate the effect and to enhance the image quality, a Geant4 simulation was performed in this work. Methods: On the basis of the principles of near-field artifact generation and elimination, coded aperture imaging of a 300 keV gamma source was simulated by Geant4 at near-field conditions with a mosaicked MURA (19×19) mask by single- and double-mode measurements, respectively. Results: The near-field artifacts were apparent in the images obtained by single-mode measurement, while they were almost eliminated by double-mode measurement. Similar results showed up in the imaging experiments with a commercial gamma camera. Conclusions: The near-field artifacts would be inhibited or even eliminated by the double-mode measurement otherwise from the conventional single-mode measurement, resulting with an enhanced signal-to-noise ratio (SNR) of reconstructed images. (authors)

[en] A precise, detailed description of the characteristics (such as flux, energy spectrum and angular distribution) of the natural cosmic-ray muons was significant for muon tomography. However, the muon characteristics may vary from day to day, and location to location, as a result of the effects of the solar cycle, geomagnetic field and atmosphere. For a comprehensive study on the effects, a Monte Carlo simulation was applied based on the 1976US model of atmosphere to explore how the flux, energy spectrum and angular distribution of muons were changed as the measuring conditions varied. The data were obtained using the code 'Cosmic RaY generator' (CRY). The results demonstrated that the flux was reduced at the solar maximum or near the equator, where the geomagnetic field blue-shifted the spectrum. As well, the flux was definitely increased at elevated locations while the mean energy dropped away. The simulation results agreed well with previous experimental data. (authors)

[en] The reaction of LiH with vapor in atmosphere and Ar was in-situ investigated by laser Raman spectroscopy and atomic force microscope (AFM), etc. Experiments show that a product layer composed of LiOH, LiOH·H₂O and Li₂CO₃ forms as a result of the immediate reactions of LiH with H₂O and CO₂. The reaction velocity differs at distinct locations. In detail, the product distribution in depth and the variation rules of Raman intensity were discussed. Growth rates of surface products at different time were measured by AFM. Owing to stress release, microcracks appear in growing process, redounding to continuous penetration of H₂O through the product layer into LiH bulk for further reactions. The reaction of LiH with H₂O was considerably dependent on humidity that even in Ar with purity up to 99.995%, LiOH was still identified. (authors)

[en] Abstract Background: Muon tomography based on multiple Coulomb scattering (MCS) has been widely used in structural detection of nuclear objects. However, for some particular objects, the tomographic method would be thwarted by failing to imaging them. Purpose:In view of the technical difficulties in structural detection of those objects, a novel method named 'Forward Comparison Method (FCM)' was proposed. Methods: Both the deformation and its scale were identified effectively by directly evaluating the evolution of muon scattering properties with respect to the object. This method, instead of the traditional inverse one, showed a methodological superiority in detection of nuclear objects with prior knowledge of the original structure. Results: Preliminary results based on a computational simulation demonstrated that FCM could be used to identify the horizontal slit in a uranium slab and evaluate its width on the magnitude of sub-millimeters, on condition that the muon flux was reasonable. Conclusion: The FCM method can be effectively applied in structural detection of particular nuclear objects of hollow structure on a satisfactory timescale. (authors)

[en] It was studied by XPS that the surface hydrolysis product LiOH of the conserved LiH reacted in sealed dry condition at the room temperature. The results show that LiOH reacts with bulk LiH to form Li₂O by the solid diffusion with the release of H₂. The reaction results in the producing of bubbling and separation of the organic coating and LiH during its dry conservation. It is found that some conserved samples are in good form without these problems because most of LiOH in the hydrolysis layer reacted with ambient CO₂ and transformed to Li₂CO₃ before surface coated with polymer. So, using CO₂ as protecting gas can make LiOH transform to Li₂CO₃. It is an effective way while machining LiH and it will be greatly attributed to preserving the materials. (authors)

[en] In present work, Tikhonov regularization method is applied to the inverse analysis of the multi-shielding layer thicknesses by taking the point source ¹⁵²Eu with single, double and three shielding layers as examples. It is shown that by comparing with the least square method, Tikhonov regularization method can provide much more accurate results. The selection of gamma-ray energy lines is the major factor influencing the inverse result relative to the deviation of absorption coefficient calculation and statistical error of the detection. (authors)

[en] Coded aperture imaging of various shaped γ sources was simulated by Geant4 toolkit, with a mosaicked MURA (19 × 19) mask. Two correlation decoding algorithms (Finely Sampled Balanced and δdecoding), as well as the iterative Maximum Likelihood-Expectation Maximization (MLEM) algorithm, were applied for digital reconstruction of the coded images. The qualities of reconstructed images were compared by calculating the contract-to-noise ratio (CNR).The results showed that each of the algorithms represented a clear, exact image for every single source and that high-quality images with a better resolution and CNR were obtained by MLEM algorithm, as the statistic noise was effectively inhibited. Accordingly, coded aperture imaging was applicable in γ camera. (authors)