Chaohui He

Level and source of 129I of environmental samples in Xi'an region, China

Iodine-129 is widely used as a tracer in various environmental practices such as monitoring of nuclear environmental safety, seawater exchange and transport, geochemical cycle of stable iodine and dating of geological events. The spatial distribution of (129)I concentration varies significantly on global scale because of anthropogenic input from nuclear activities coupled with scarcity of data on environmental (129)I variability in many parts of the world including Asia. Here we report new data on (129)I and (127)I concentrations in soil, vegetation, river water and precipitation collected from Xian area, China. The results indicate values for environmental (129)I/(127)I ratios in the investigated area range from 1.1×10(-10) to 43.5×10(-10) with a mean of 20.6×10(-10), which is 1-3 orders of magnitude lower than the ratios observed in Europe, but comparable with those observed in the locations far from direct effect of point release sources and at similar latitude. The main source of (129)I in the investigated area is attributed to the global fallout of both atmospheric nuclear weapons testing and long distance dispersion of fuel reprocessing releases.

Application of NKF-6 zeolite for the removal of U(VI) from aqueous solution

To better understand the application of NKF-6 zeolite as an adsorbent for the removal of U(VI) from radionuclides and heavy metal ions polluted water, herein, NKF-6 zeolite was employed to remove U(VI) at different experimental conditions. The influence of solid/liquid ratio, contact time, pH, ionic strength, humic substances and temperature on sorption of U(VI) to NKF-6 zeolite was investigated using batch technique under ambient conditions. The experimental results demonstrated that the sorption of U(VI) on NKF-6 zeolite was strongly dependent on pH. The sorption property of U(VI) was influenced by ionic strength at pHxa0<xa07.0, whereas was independent of ionic strength at pHxa0>xa07.0. The presence of fulvic acid or humic acid promoted the sorption of U(VI) on NKF-6 zeolite at low pH values while restrained the sorption at high pH values. The thermodynamic parameters (i.e., ΔS0, ΔH0, and ΔG0) calculated from the temperature-dependent sorption isotherms demonstrated that the sorption process of U(VI) on NKF-6 zeolite was endothermic and spontaneous. At low pH values, the sorption of U(VI) was dominated by outer-sphere surface complexation and ion exchange with Na+/H+ on NKF-6 zeolite surfaces, while inner-sphere surface complexation was the main sorption mechanism at high pH values. From the experimental results, one can conclude that NKF-6 zeolite can be used as a potential adsorbent for the preconcentration and solidification of U(VI) from large volumes of aqueous solutions.

Impact of Bias Conditions on Total Ionizing Dose Effects of

The effect of bias condition on total ionizing dose (TID) of Silicon-Germanium heterojunction bipolar transistors (SiGe HBTs) is investigated. The SiGe HBTs are set at forward, saturated, cutoff, and all-grounded biases during 60Coγ irradiation. After each irradiation stops, the forward Gummel characteristic and inverse Gummel characteristic are measured, and a 3-D simulation of TID for SiGe HBT is performed. The mechanism of TID in different bias conditions is obtained by analyzing normalized excess base current. The results show that the TID damages are different at various irradiation biases of the SiGe HBT, and the worst bias between forward and inverse Gummel characteristics exhibits inconsistently. The reason could be attributed to different defects produced and accumulated in oxide layers by irradiation at various bias conditions. To be specific, the oxide trap charges (Not) in emitter/base (E/B) Spacer is important to the forward Gummel characteristic, yet the Not in LOCOS determines the inverse Gummel characteristic. However, after long time irradiation, the interface states (Nit) both in E/B Spacer and LOCOS dominate the damage to the SiGe HBT despite in forward Gummel mode or inverse Gummel mode.

^{60}{\hbox{Co}}\gamma

A rapid and simple method was developed for speciation analysis of (129)I in seawater by selective coprecipitation of carrier-free iodide and accelerator mass spectrometry (AMS) measurement of (129)I. Iodide was separated from seawater and other species of iodine by coprecipitation of AgI with Ag2SO3, AgCl, and AgBr by addition of only 100 mg/L Ag(+) and 0.3 mmol/L NaHSO3 at pH 4.2-5.5. The separation efficiency of iodide was more than 95%, and crossover between (129)IO3(-) and (129)I(-) fractions is less than 3%. Iodate and total inorganic iodine were converted to iodide by use of NaHSO3 at pH 1-2 and then separated by the same method as for iodide. Ag2SO3 in the coprecipitate was removed by washing with 3 mol/L HNO3 and the excess AgCl and AgBr was removed by use of diluted NH3, and finally a 1-3 mg precipitate was obtained for AMS measurement of (129)I. The recovery of iodine species in the entire procedure is higher than 70%. Six seawater samples collected from the Norwegian Sea were analyzed by this method as well as a conventional anion-exchange chromatographic method; the results from the two methods show no significant difference (p = 0.05). Because only one separation step and fewer chemicals are involved in the procedure, this method is suitable for operation on board sampling vessels, as it avoids the transport of samples to the laboratory and storage for a longer time before analysis, therefore significantly improving the analytical capacity and reliability of speciation analysis of (129)I. This improvement can stimulate oceanographic tracer studies of (129)I.

in SiGe HBT

Abstract The incorporation and the diffusion of helium (He) with and without the intrinsic vacancy defects in the cubic ZrO 2 are investigated through the first-principles total-energy calculations, in which the projector-augmented-wave (PAW) method with the generalized gradient approximation (GGA) is adopted. Ab initio calculations are carried out to identify the dominant defects and understand their electronic properties as well. Both the intrinsic oxygen interstitials and the oxygen vacancies in the cubic ZrO 2 show the negative- U behavior. The incorporation energy of He impurity indicates that it is preferable to occupy the Zr vacancy at first, whereas the solution energy suggests that He would be accommodated in the interstitial site at the thermodynamic equilibrium concentration. By calculating the He migration energies corresponding to both the interstitial diffusion and the vacancy assisted diffusion, we suggest that it is most likely to diffuse by hopping through a single vacancy. Remarkably, our calculated vacancy-assisted diffusion energy barrier of He is consistent well with the experimental measurement.

Speciation analysis of 129I in seawater by carrier-free AgI-AgCl coprecipitation and accelerator mass spectrometric measurement.

A method has been developed for speciation analysis of ultra low level (129)I in soil using sequential extraction combined with coprecipitation for separation of carrier free iodine and AMS measurement of (129)I. Two loess profiles collected from northwest China were analyzed for species of (129)I and (127)I. Similar partitioning of (129)I and (127)I was observed in the loess profiles, the distribution of iodine isotopes followed an order of organicxa0>xa0leachablexa0>xa0reduciblexa0>xa0residue. The (129)I concentrations and (129)I/(127)I ratios decreased exponentially with the depth, and 2 orders of magnitude lower in the deepest layer (60 and 90xa0cm) compared with the top layer, indicating a significant contribution of anthropogenic input in the upper layer, and high retention of (129)I in soil. The mobility of (129)I in different fractions decreased in an order of leachablexa0>xa0organicxa0>xa0oxidesxa0>xa0residue. The results suggest that migration of iodine downwards in the soil profile is a slow process; the oxides and residue are the less mobile fractions of iodine.

First-principles study of the incorporation and diffusion of helium in cubic zirconia

The sorption behavior of Se(IV) on Fe- and Al-modified bentonite is studied through batch experiments. In order to introduce active centers for Se(IV) sorption, bentonite was modified with iron, iron oxocations and aluminum oxocations at 400, 600 and 800xa0°C. It was found that calcined temperature had great effect on the sorption with above 80xa0% sorption at 400xa0°C, whereas with only 5xa0% sorption at 800xa0°C. The sorption capacities for Se(IV) were 112.5xa0mg/g by FeOH-B, 60.1xa0mg/g by AlOH-B and 71.9xa0mg/g by Fe-B, respectively. The pH-dependent and ionic strength-independent Se(IV) sorption on these modified bentonites demonstrated that the sorption mechanism of Se(IV) was inner-sphere surface complexation at low pH values.

Speciation and migration of 129I in soil profiles

The atomic hydrogen adsorption on Zr(0001) surface is systematically investigated by using density functional theory within the generalized gradient approximation and a supercell approach. The coverage dependence of the adsorption structures and energetics is studied in detail for a wide range from 0.11 to 2.0 monolayer. At low coverage of 0<Θ≤1.0, the most stable adsorption site is identified as the on-surface hcp site followed by the fcc site, and the adsorption energy gradually increases with the coverage, thus, indicating the higher stability of on-surface adsorption and the tendency to form H clusters. The origin of this stability is carefully analyzed by the projected density of states and the charge distribution showing the Zr-H chemical bonding with a mixed ionic/covalent feature during the surface hydrogenation. In addition, the minimum energy paths as well as the activation barriers of the on-surface diffusion and the penetration from on-surface sites to subsurface sites are also calculated. At ...

Sorption of Se (IV) on Fe-and Al-modified bentonite

Abstract A molecular dynamics study has been performed to investigate the generation and evolution of damage states in irradiated β-SiC at high temperature. It is found that most of the C antisites (SiC) are created during the early collisional phase, while the Si antisites (CSi) are significantly produced during the thermal spike phase. A modified near-neighbor point defect density (NPDD) is introduced to study the spatial aggregation of different defects during the displacement cascades, and feature of defect clusters evolution is analyzed in details. The dominated types of vacancy clusters after the displacement cascades are two- and three-size chainlike ones. And the vacancy NPDD (V-NPDD) decreases as the recoil energy increases. Furthermore, after the thermal spike phase, there is an additional annealing process during which the interstitials and antisites turn into defect clusters, respectively.

First-principles study of atomic hydrogen adsorption and initial hydrogenation of Zr(0001) surface

Abstract In this paper, experimental methods are emphatically described for measuring the proton single event effects (SEE) in Xilinx Zynq-7010 system-on chip. Experimental data are presented showing that low energy (3xa0MeVxa0≤xa0Energyxa0≤xa010xa0MeV) proton irradiation can cause single event effects in different hardware blocks of Xilinx Zynq-7010 SoC, including D-Cache, programmable logic (PL), arithmetic logical unit (ALU), float point unit (FPU) and direct memory access (DMA). Moreover, the sensitivities of different hardware blocks to single event effects are different. Finally, the Stopping and Range of Ions in Matter (SRIM) software calculations show the possible reasons for this difference.