类水滑石材料在核废水处理领域的应用

核能已成为我国能源结构的重要组成部分, 但含放射性物质的废水所带来的危害不容忽视. 如何高效解决核废水污染问题迫在眉睫. 类水滑石材料是一类阴离子型粘土化合物, 因其层板组成及层间阴离子种类的可调控性、 较大的比表面积及粒径和形貌的可调控性等特点已在含放射性核素废水的处理中崭露头角. 本文主要阐述了类水滑石材料对废水中放射性核素的吸附行为及其作用机制, 探讨了存在的问题及可能的解决方法, 并对其发展前景进行了展望.     

Acoustic Radiation Force Impulse-Imaging for the evaluation of the thyroid gland: a limited patient feasibility study

Purpose

Real-time tissue elastography, a qualitative elastography method, has shown promising results in the diagnostic work up of thyroid nodules. However, to our knowledge no study has evaluated a quantitative elastography method in the thyroid gland. The present study is a feasibility study evaluating Acoustic Radiation Force Impulse-Imaging, a novel quantitative elastography method in the thyroid gland.

Methods

ARFI-imaging involves the mechanical excitation of tissue using short-duration acoustic pulses to generate localized displacements in tissue. The displacements induce a lateral shear-wave propagation which is tracked using multiple laterally positioned ultrasound “tracking“ beams. Inclusion criteria were: thyroid nodules ?1 cm, non-functioning or hypo-functioning on radionuclide scanning, and cytological/histological assessment of thyroid nodule as reference method. All patients received conventional ultrasound, and examination of the thyroid gland including Power Doppler Ultrasound using a 9 MHz linear transducer, in addition real-time elastography (RTE) was performed at 9 MHz frequency and ARFI-imaging was performed at 4 MHz using Siemens (ACUSON S2000) B-mode-ARFI combination transducer.

Results

Sixty nodules in 55 patients were analyzed. Three nodules were papillary carcinoma. The stiffer the tissue the faster the shear wave propagates. The results obtained indicated that the shear wave velocity in thyroid lobes ranged between 0.5 and 4.9 m/s. The median velocity of ARFI-imaging in the healthy nodule-free thyroid gland, as well as in benign and malignant thyroid nodules was 1.98 m/s (range: 1.20-3.63 m/s), 2.02 m/s (range: 0.92-3.97 m/s), and 4.30 m/s (range: 2.40-4.50 m/s), respectively. While no significant difference in median velocity was found between healthy thyroid tissue and benign thyroid nodules, a significant difference was found between malignant thyroid nodules on the one hand and healthy thyroid tissue (p = 0.018) or benign thyroid nodules (p = 0.014) on the other hand. Specificity of ARFI-imaging for the differentiation of benign and malignant thyroid nodules was comparable with RTE (91-95%).

Conclusions

ARFI can be performed in the thyroid tissue with reliable results.     

A computational method for the hydrodynamics of fractured-porous media

A numerical method based on the boundary-fitted finite difference method (BFDM) is presented in this paper. The boundaries are external (the boundary of the physical domain) and internal (which corresponds to the fracture network). The difference between this approach and the usual one lies in the inclusion of discrete fractures in the volume that represents the porous medium. The numerical model has been used in the prediction of the flow pattern in several internationally recognized verification cases and applied to the solution of hypothetical problems of interest to us in the field of nuclear waste repository modelling. The results obtained show that the numerical approach considered gives accurate and reliable predictions of the hydrodynamics of fractured-porous media, thus justifying its use for the above-mentioned studies.     

Reductive immobilization and long-term remobilization of radioactive pertechnetate using bio-macromolecules stabilized zero valent iron nanoparticles

Carboxymethyl cellulose-and starch-stabilized nZVI nanoparticles were prepared and showed high efficiency for reductive immobilization of ⁹⁹TcO₄^- in simulated groundwater.     

Natural radionuclide concentrations in soils around Baoji coal-fired power plant,China

Radionuclides are released together with fly ash from the coal-fired power plant and thus add to the natural radiation. Fifty soil samples were collected around the Baoji coal-fired power plant from 25 locations and the natural radionuclide concentrations were determined by a gamma ray spectrometric system. The results show that the activity concentrations in soil samples range from 12.54 to 40.18 Bq kg^?1, 38.02 to 72.55 Bq kg^?1 and 498.02 to 1126.98 Bq kg^?1 for ²²⁶Ra, ²³²Th and ⁴⁰K with the mean values of 27.35, 52.66 and 764.72 Bq kg^?1, respectively. In order to evaluate the radiological hazard of the natural radioactivity, the radium equivalent activity (Ra_eq), the absorbed dose rate (D) and the annual effective dose rate have been calculated and compared with the internationally approved values. The radium equivalent activity in all the soil samples is lower than the safe limit set in the Organization for Economic Cooperation and Development report (370 Bq kg^?1). The average value of the calculated dose rates is higher than the global average value 55 nGy h^?1, and the calculated annual effective dose rate is significantly lower than the average annual external effective dose rate (460 μSv y^?1) of the normal background radiation.     

First approach to radionuclide mixtures quantification by using plastic scintillators. Influence of the diameter of the plastic beads

Recent studies have evaluated the capability of plastic scintillation (PS) as an alternative to liquid scintillation (LS) in radionuclide activity determination without mixed waste production. In order to complete the comparison, we now assess the extent to which PS can be used to quantify mixtures of radionuclides and the influence of the diameter of the plastic scintillation beads in detection efficiency.

The results show that the detection efficiency decreases and the spectrum shrink to lower energies when the size of the plastic scintillation beads increases, and that the lower the energy of the beta particle, the greater the variation takes place. Similar behaviour has been observed for beta–gamma and alpha emitters.

Two scenarios for the quantification of mixtures are considered, one including two radionuclides (¹⁴C and ⁶⁰Co) whose spectra do not overlap significantly, and the other including two radionuclides (¹³⁷Cs and ⁹⁰Sr/⁹⁰Y), where the spectra of one the isotopes is totally overlapped by the other The calculation has been performed by using the conventional window selection procedure and a new approach in which the selected windows correspond to those with lower quantification errors. Relative errors obtained using the proposed approach (less than 10%) are lower than those of the conventional procedure, even when a radionuclide is completely overlapped, except for those samples with extreme activity ratios that were not included in the window optimization process.     

Covalent Organic Frameworks(COFs) for Sequestration of99TcO4–

Covalent organic frameworks(COFs), as a class of crystalline porous materials with periodic lattices and porous structures, have received extensive attention in the fields of gas storage and separation, energy storage, catalysis and optoelectronics and so on. However, COFs are still in their infancy in the field of nuclear waste treatment, especially for sequestration of long-live problematic radionuclides, such as ⁹⁹Tc. Battle of decontamination of pertechnetate(TcO₄^–), a main existence of ⁹⁹Tc under aerobic environments, is far from finished. In this review, recent progresses of COFs and some relative materials in the sequestration of pertechnetate, and perspective on surmounting the unmet issues are elucidated.