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Optimized lightweight, compact and high temperature sustaining shielding materials for neutron and gamma radiation were developed by genetic algorithms (GA) combined with the Monte Carlo N-Particle (MCNP) code. A series of samples were designed according to the method. Deep penetration tests by the MCNP code were completed. The results show that the designed samples have more advantages related to the radiation shielding effects in comparison with PB202 and KRAFTON-XP3, especially the Cakes with multi-layers structures of the Fe-Interlayer-Pb have excellent performance. Taking into account the ratios designed of components among elements in the material, the manufacturing process of polymer with nano-Ti[O.sub.2] was studied experimentally by differential scanning calorimetry (DSC). Several samples have been tested. The attenuation experiments on the samples were carried out using tandem electrostatic accelerator neutron source, spontaneous fission neutron source of [sup.252]Cf and [gamma]-rays source of [sup.60]Co. The experimental results verify the correctness of optimal design and craft. The Cakes are quite suitable for applications in the practices of nuclear science and technology. Index Terms--Composite, gamma rays, genetic algorithms, Monte Carlo, neutrons, shielding.

Employing the DFT+U framework we investigate the thermodynamic stability of U 3 O 8 (100) surface. The most stable structure is predicted to gradually turn from the under-stoichiometric 0 6 - to the over-stoichiometric 5 6 -slab as the oxygen chemical potential increases, showing a continuous surface oxidation process. Oxygen atoms are found to always firstly adsorb on the lower oxidized U ions. Due to the polarity compensation, significant modification of surface charge presents on considered terminations, which is transferred via both U-5 f and O-2 p states, implying the nature of U 3 O 8 as an intermediate state between the Mott–Hubbard and charge-transfer materials. It is also shown that the displacement of the outmost U 6 O 10 layer and the surface energy are strongly related to the redistribution of surface charge. The static effect between charged layers is the major factor which influences the layer displacement. The increase in surface energy is shown to be roughly linearly dependent on the amount of the surface charge transfer. [Display omitted] • The surface chemistry of U 3 O 8 (100) is dramatically influenced by polarity compensation. • U 3 O 8 (100) surface is predicted to transform from under- to over-stoichiometric as μ O increases. • U(2) is much more favorable in adsorbing oxygen atoms than U(1). • The charge transfer is accomplished via U-5 f and O-2 p states together. [ABSTRACT FROM AUTHOR]

A systematic investigation of the transport of I in compacted GMZ bentonite containing Fe-Oxides, Fe-minerals or CuO additive was carried out by through-diffusion method. The obtained results indicate that all of the additives have positive effects on retarding the I diffusion in compacted GMZ bentonite. Especially for the CuO additive, the corresponding effective diffusion coefficient is greatly reduced. It is mainly attributed to the particular interactions between the metal ions introduced by additives and iodide ions. [ABSTRACT FROM AUTHOR]

Humic acid is ubiquitous in soils and water. It affects the migration of radionuclides by complexation or redox reactions. The effect of humic acid on the diffusion of ReO in GMZ bentonite was investigated at dry density from 1,300 to 1,800 kg/m. The effective diffusion coefficient D and rock capacity factor α were measured by through-diffusion method. The D decreased from 5.5 to 0.59 × 10 m/s and α decreased from 0.2 to 0.12 with the dry density increasing from 1,300 to 1,800 kg/m. The retardation factor R in GMZ bentonite at three dry densities was obtained, which were less than one. Archie's law was used to describe the relationship between accessible porosity ε and D. An empirical parameter n ( n = 2.2 ± 0.2) was obtained for Re diffusion in GMZ bentonite in the presence of humic acid. [ABSTRACT FROM AUTHOR]