Remains of 137Cs contamination in the city of Goiânia, Brazil

The results of measurements, performed in 1999, of the remaining 137Cs contamination in some of the sites where fragments of a radioactive source of a teletherapy unit had been manipulated in 1987 are presented. This episode occurred in the city of Goiania, during Brazil's worst radiological accident ever reported. Using the technique of gamma ray spectrometry, analyses of both surface and profile soil and vegetable samples were made. High values of 137Cs activity per unit mass were found in soil layers at depths between 10 and 40cm from the surface. Some values exceeded by up to eight times the action level of 22.5 kBq x kg(-1) proposed by the Brazilian National Nuclear Energy Commission (CNEN) during the decontamination process at the time of the accident, for the first year after the accident. Absorbed dose rates at 1 m above the ground were calculated from the data of 137Cs concentration in the soil and compared with those obtained from in situ gamma ray spectrometry and from thermoluminescence dosimetry.     

~(137)Cs γ射线空气比释动能基准石墨空腔电离室的研制

根据Bragg-Gray理论研制了圆柱形石墨空腔电离室,用于~(137)Cs空气比释动能基准的建立。通过理论计算灵敏体积内部电场分布,优化了电离室壁和收集极之间接地保护的结构设计,在此基础上,对研制的电离室的饱和曲线、本底电流以及稳定性等电学性能进行了测试,其结果表明完全达到设计要求。对电离室的各项修正因子进行了理论计算和实验测量,实现了~(137)Cs空气比释动能的量值复现,其合成标准不确定度为0.25%。     

Measurement of the <Superscript>137</Superscript>Cs concentration by its own β-radiation using liquid scintillation spectrometry

The possibility of measuring the ¹³⁷Cs concentration in seawater by its own β-radiation using liquid scintillation spectrometry after preliminary sorption on cellulose fiber impregnated with copper(II) ferrocyanide was studied. This measurement procedure allows the ¹³⁷Cs detection efficiency to be increased to 50% and the sample volume to be decreased from 1000 (as in γ-ray spectrometry) to 50 L and less.     

Studies on the current 137Cs body burden of children in Belarus--can the dose be further reduced?

After the Chernobyl reactor accident wide areas of Belarus were contaminated with radioactive fallout. The verification and documentation of the long-term development of radiation doses is still going on. A population group of special concern are the children living in contaminated regions. The annual dose limit of 1 mSv is still exceeded in some cases, essentially due to high body burdens of (137)Cs as indicated by screening measurements with portable incorporation monitors. In this situation the evaluation of possible dose reduction measures in addition to the control of food contamination is being investigated. Special attention is given to the therapeutic application of a pectin preparation (Vitapect), for which a dose-lowering effect is presumed by Belarusian scientists. In a placebo-controlled double-blind study, several groups of contaminated children received a pectin compound named Vitapect for a two-week period during their stay in a sanatorium. For comparison the same number of control groups were given a placebo preparation. The (137)Cs body burden of the children was measured at the beginning and the end. The mean relative reduction of the specific activity within the Vitapect groups was found to be approximately 33%, whereas the specific activity of the children who received a placebo decreased only by approximately 14%, due to clean food supply. It is known that pectins chemically bind cations like caesium in the gastrointestinal tract and thereby increase faecal excretion. Theoretical calculations based on this assumption and considering metabolism processes are qualitatively consistent with the experimentally found retention of radiocaesium in the human body after pectin treatment.     

Optical absorption and thermoluminescence of barytes single crystals irradiated with γ-rays

The optical absorption in the wavelength region 200 to 800 nm of barytes single crystals before and after -ray irradiation for different times has been measured. The thermoluminescence (TL) of the irradiated crystals has also been studied. -ray irradiation produces absorption bands at 590 and 370 nm possibly due to Ba⁺ and (SO₄)^– centres, respectively. Partial thermal bleaching experiments carried out on these absorption bands show that the absorption in both bands gradually decreases up to 200° C beyond which it falls rapidly. The -ray irradiated barytes exhibits TL peaks at 90, 180 and 208° C. An attempt is made to understand the results.     

Variation in Creep Rupture of γ′ Strengthened Superalloys with Stacking Fault Energy of Matrices

The correlation between the creep rupturebehaviour and the stacking fault energy of matricesof γ′strengthened superalloys has been studied dur-ing constant load creep.At high temperature andintermediate stress,the creep rupture time andstrain strongly depend on the stacking fault energyof matrices rather than the creep friction stress,butat higher stress,the role of grain boundary carbidesbecomes more obvious.However,in the considerably extensive stressrange investigated here,the mean creep rate is apower function of the stacking fault energy ofmatrices and the power index decreases with in-creasing initial applied stress.Particularly,at inter-mediate stresses the product of this index and theinitial applied stress compensated by the shearmodulus is same for two series of superalloys.Hence,this product may be a criterion predictingthat the matrix deformation controls high tempera-ture creep rupture.     

Sorption of <Superscript>137</Superscript>Cs from seawater onto resorcinol–formaldehyde resin

Sorption of ¹³⁷Cs from seawater onto a selective cation exchanger based on resorcinol–formaldehyde resin was studied. The maximal distribution coefficient of ¹³⁷Cs at the ratio S: L = 1: 1000 is (4.1–4.5) × 10³ cm³ g^–1. The sorption-selective characteristics of the resin are negatively affected by alkaline earth meal ions. In the dynamic regime, the operation life of the resorcinol–formaldehyde resin exceeds 700 bed volumes with more than 95% efficiency of cesium sorption. More than 95% of ¹³⁷Cs is eluted with a 1–3 M HNO₃ solution. The eluate volume does not exceed 10 bed volumes.     

Molecular Dynamics Simulation of Tensile Deformation and Fracture of γ-TiAl with and without Surface Defects

Molecular dynamics simulation of uniaxial tension along [001] has been performed to study the influence of various surface defects on the initiation of plastic deformation and fracture of γ-TiAl single crystals.The results indicate that brittle fracture occurs in perfect bulk; surfaces and edges will be detrimental to the strength of materials and provide dislocation nucleation site. The defects on surfaces and edges cause further weakening with various effects depending on defect type, size, position and orientation,while the edge dimples are the most influential. For γ-TiAl rods with surface dimples, dislocations nucleate from an edge of the rod when dimples are small, dimple dislocation nucleation occurs only when the dimples are larger than a strain rate dependent critical size. The dislocations nucleated upon [001]tension are super dislocations with Burger vectors 011] or 1/2 112] containing four 1/6 112 partials. The effects of surface scratches are orientation and shape sensitive. Scratches parallel to the loading direction have little influence, while sharp ones perpendicular to the loading direction may cause crack and thus should be avoided. This simulation also shows that, any type of surface defect would lower strength,and cause crack in some cases. But some may facilitate dislocation nucleation and improve ductility of TiAl if well controlled.     

Increasing the Resolution and SNR of an ADC＇s Measurement with a Method of OverSampling and Averaging

By analyzing the theory of over-sampling and averaging, the conclusion is educed that white noise accompanies the signal and the addition of each bit of resolution can be achieved via a fourfold sampling frequency. The addition of each bit will approximately increase the SNR （signal to noise ratio） to 6dB.     

Variation of the optical energy gap with γ-radiation and thickness in Bi-thin films

The effect of -radiation and thickness on the optical energy gap of Bi-thin films has been investigated by measuring their optical absorbance. The measurements were carried out on thermally evaporated films having thicknesses in the range 5–20 nm. Different -radiation doses were used ranging from 0–300 Mrad. The optical energy gap as well as the absorption coefficient were found to be -dose dependent.     

One-step functionalization of multi-walled carbon nanotubes with Ag/polymer under γ-ray irradiation

We reported an easy strategy of using γ-ray irradiation to functionalize multi-walled carbon nanotubes (MWCNTs) without the use of aggressive acid treatment, all in a single processing step. In this paper, we tried to decorate MWCNTs with Ag nanoparticles relying on covalently bonded polymers, via one-step covalent grafting of the polymer to the surface of MWCNTs, and simultaneous reducing of Ag(+) ions to Ag which are then efficiently anchored onto the MWCNTs. Herein, the polymer involved was the commercially available polymer poly(vinyl alcohol) (PVA) and two of its derivatives, polyvinylacetone with ketalization degree D(H) = 0.22 and 0.53. It is envisioned that this simple but efficient method could be extended to fabricate other CNT-based hybrids for both theoretical study and applications in biological and technological fields.     

Visible Light Photocatalytic Properties of Metastable γ-Bi_2O_3 with Different Morphologies

The metastable γ-Bi_2O_3 photocatalysts with different morphologies were fabricated by means of a chemical precipitation method.The microstructure of as-prepared samples was characterized by X-ray diffraction,transmission electron microscopy and ultraviolet-visible diffusion reflectance spectroscopy.The photocatalytic performance of Bi_2O_3 powder was evaluated using rhodamine B as a model pollutant under visible light irradiation.The visible light photocatalytic activity of Bi_2O_3 with different morphologies is as follows,nanorod nanorod/nanoflake N doped TiO_2 irregular particle agglomerated particle.The γ-Bi_2O_3 shows the best photocatalytic performance and it can effectively degrade 97%RhB within 60 min.     

A facile solvothermal route to synthesis of γ-alumina with bundle-like and flower-like morphologies

Boehmite with bundle-like morphology assembled from nanofibres has been successfully synthesized by solvothermal method from AlCl₃·6H₂O in ethylene glycol (EG) at 200 °C for 10 h. Using 1,4-Butanediol instead of EG, the Al₁₁(OH)₃₀Cl₃ with flower-like morphology assembled from nanosheets was obtained at 200 °C for 6 h. The γ-alumina with similar morphology was obtained by thermal decomposition of the boehmite or Al₁₁(OH)₃₀Cl₃ at 500 °C for 3 h in air. The products were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectrometry (FTIR), transmission electron microscopy (TEM), and thermogravimetric analysis (TG). The method is simple and does not need any surfactant or template or base.     

Simultaneous Measurement of Torsional Oscillator and?NMR in Solid 4He with 10?ppm of 3He

We have performed the simultaneous measurement of torsional oscillator and NMR in solid ⁴He with 10 ppm of ³He at 3.6 MPa. In this solid, NCRI response appears below about 400 mK. NMR measurement shows that there is the same kind of phase-separated ³He cluster which is found in our previous measurement in solid ⁴He with over a hundred ppm of ³He. When we warm the solid above the phase separation temperature, the cluster disappears gradually. Below and above the phase separation temperature, the distribution of ³He atoms changes significantly with long time constant, which is as long as a day. However, even in such a long time span, we do not observe any systematic changes in the torsional oscillator response. This result suggests that the phase separation and related changes of the distribution of ³He is not directly related to the impurity effect of the NCRI response.     

Increasing the Resolution and SNR of an ADC′s Measurement with a Method of Over- Sampling and Averaging

1IntroductionFor many applicable systems, the cost is greatly increased by adopting expensive extra ADC to raisethe measuring resolution. Through studying the method of over sampling and averaging, the reasolu-tion of A/D conversion and SNR can be raised without extra ADC.2Circuit modelConverting ADC may cause various noises, for instance, thermal noise, power voltage and standardvoltage variations, phase noises caused by fluctuation of the sampling clock, quantitative noise dueto quanti…     

Effect of (n, γ) and (n, α) reactions of framework atoms on the (n, γ) recoils in Ba and Cs cations in high-silica zeolites

The effects of (n, γ) and (n, α) reactions of framework atoms on the fate of (n, γ) recoil species ¹³¹Ba²⁺ and ¹³⁴Cs⁺ from Ba²⁺ and Cs⁺ loaded in high-silica aluminosilicate and borosilicate zeolites (boron-zeotypes) have been studied. Studies were made of the recoil from “open to locked-in” and “locked-in to open” sites. In open to locked-in recoil, target ions were eluted with efficiencies of 90% where only (n, γ) processes were in operation, but in the presence of (n, γ) and (n, α) reactions, the efficiency fell to 80%. For locked-in to open site recoil, the corresponding efficiencies were in the ranges 50–60% and 40–50%. The effect of calcination temperature on the exchange of cations present was also ascertained. The high-silica zeolites used were synthesized according to published methods and were characterized by XRD, i.r., SEM, and t.g.-d.t.g./d.s.c. techniques, and all were found to be crystalline. In boron-zeotype materials, the magnitude of (n, α) damage was increased by the use of ¹⁰B isotope.     

Simulation of rafting type and stress distribution in nickel-based superalloys with different volume fractions of γ′ phase

A representative volume element is introduced to represent the microstructure of γ/γ′ morphology with periodic boundary conditions to formulate the full mode of the micromechanical analysis. [0 0 1]-oriented alloys with γ′ volume fractions from 60 to 70% are simulated under tensile loading. A raft criterion is implemented into the user subroutine to predict the rafting type. The misfit stress is considered by different thermal expansion coefficients of the two phases. It is very high in γ phase and slightly decreases with the increasing of γ′ volume fraction. The stress distributions in the two phases change during creep deformation. The creep crack initiation time slightly increases with the increase of γ′ volume fraction. The stress components decrease with the increasing of γ′ volume fraction at the beginning and change due to the stress redistribution during creep loading.