摘要:
Accurate measurement of unattached radon progeny is important for dose evaluation of radon exposure. For quality control of field surveys, a series of comparison measurements were carried out using three commercial unattached radon progeny monitors in real environments as well as in a radon chamber. The results show that the radon equilibrium equivalent concentrations (EECs) of different monitors agree very well, mostly within +/- 3.0% where there is no thoron progeny interference in the radon chamber. However, the unattached fraction of radon progeny is not so consistent, and the relative difference is 3.3% similar to 39.5% in different environments. The unattached fraction of radon progeny is affected by aerosol concentration. Anomalously high unattached fraction was found in the environment with extremely high humidity and low aerosol concentration. For accurate measurement of unattached radon progeny, specific attention should be paid to the collection efficiency of unattached radon progeny and the interference of attached radon progeny on a wire screen.
摘要:
To understand the physical and chemical characteristics, particle size distribution and sources of size-separated aerosols in Lhasa, which is located on the Tibetan Plateau (TP), six sizes of aerosol samples were collected in Lhasa in 2014. Ca(2+), NH4(+), NO3(-), SO4(2-) and Cl(-) were the dominant ions. The ratio of cation equivalents (CE) to anion equivalents (AE) for each particle size segment indicated that the atmospheric aerosols in Lhasa were alkaline. SO4(2-) and NO3(-) could be neutralized by Ca(2+), but could not be neutralized by NH4(+), according to the [NH4(+)]/[NO3(-)+SO4(2-)] and [Ca(2+)]/[NO3(-)+SO4(2-)] ratios. Mobile sources were dominant in PM0.95-1.5, PM1.5-3 and PM3-7.2, while stationary sources were dominant in the other three size fractions according to the [NO3(-)]/[SO4(2-)] ratios. The particle size distribution of all water-soluble ions during monsoon and non-monsoon periods was characterized by a bimodal distribution due to the different sources and formation mechanisms, and it was revealed that different ions had different sources in different seasons and different particle size segments by combining particle size distribution with correlation analysis. Source analysis of aerosols in Lhasa was performed using the Principal component analysis (PCA) for the first time, which revealed that combustion sources, motor vehicle exhaust, photochemical reaction sources and various types of dust were the main sources of Lhasa aerosols. Furthermore, Lhasa's air quality was also affected by long-distance transmission, expressed as pollutants from South Asia and West Asia, which were transmitted to Lhasa according to backward trajectory analysis.
摘要:
Two fusion methods were established for rapid determination of Pu in soil and sediment samples. The methods consisted of NH4HSO4 or NH4HF2 fusion procedures incorporated with procedures for CaF2/LaF3 co-precipitation, extraction chromatography and SF-ICP-MS measurement. The fusion procedures were done on a portable hot plate instead of in a cumbersome muffle furnace and took only 15min heating-up time from room temperature to 250 degrees C and 15min fusion time at 250 degrees C. Chemical recoveries of Pu after completing the NH4HSO4 and NH4HF2 fusion methods for 0.5-1g sample were approximately 70% and more than 90%, respectively, and decreased with the increase of sample weight from 0.5g to 5g. Sediment samples were pre-ignited at different temperatures ranging from 450 degrees C to 1000 degrees C to form refractory fractions of Pu, with which the dissolution rates of Pu by the NH4HSO4 and NH4HF2 fusion were investigated. With the increase of pre-ignition temperature of the sediment samples, the dissolution rates of Pu from the samples prepared by NH4HSO4 fusion declined dramatically from near 100% for 450 degrees C to 8% for 1000 degrees C. In contrast, the NH4HF2 fusion was capable of completely releasing Pu from samples that were pre-ignited at temperatures over 450 degrees C to 1000 degrees C, which was comparable to releases obtained by the hazardous and time-consuming HNO3-HF digestion, and was superior to the conventional HNO3 digestion. Additionally, because HF is not used in any procedure of the NH4HF2 fusion, a safer and greener alternative to NH4HSO4 fusion and HNO3-HF digestion is realized for rapid Pu determination in environmental samples for nuclear emergency response and application in environmental studies.
摘要:
本文阐述了单球中子谱仪的原理,介绍了基于单慢化球和19对6Li-7Li闪烁体探测器构成的单球中子谱仪的结构及解谱方法,使用蒙特卡罗中子榆运程序模拟了单球中子谱仪的中子响应函数.计算结果表明,该谱仪具有较好的空间对称性,能根据谱仪中各探测器的计数对源的大致方位进行判断;模拟了单球谱仪在241 Am-Be源照射下各探测器的计数,使用Unfolding with Maxed and Gravel (UMG)解谱程序在不同解谱算法以及初始谱的情况下对模拟数据进行解谱计算,在使用最大熵散发以及与源项相同的预置谱的情况下,解谱结果最为准确,验证了响应函数的准确性.
关键词:
organic carbon;elemental carbon;water-soluble organic carbon;size distribution
摘要:
In this paper, we intensively collected atmospheric particulate matter (PM) with different diameters (size ranges: <0.49, 0.49–0.95, 0.95–1.5, 1.5–3.0, 3.0–7.2, and >7.2 μm) in Lhasa during the monsoon and non-monsoon seasons. The results clearly showed that the concentrations of PM, organic carbon (OC), elemental carbon (EC), and water-soluble organic carbon (WSOC) during the non-monsoon season were much higher than the concentrations during the monsoon season. During the monsoon season, a bimodal size distribution of the OC and WSOC, which were at <0.49 μm and >7.2 μm, respectively, and a unimodal size distribution at <0.49 μm for the EC were observed. However, during the non-monsoon season, there was a trimodal size distribution of the OC and WSOC (<0.49 μm, 1.5–3.0 μm, and >7.2 μm), and a unimodal size distribution of the EC (<0.49 μm). Possible sources of the carbonaceous components were revealed by combining the particle size distribution and the correlation analysis. OC, EC, and WSOC were likely from the photochemical transformation of biogenic and anthropogenic VOC, and the incomplete combustion of biomass burning and fossil fuels at <0.49 μm, whilst they were also likely to be from various types of dust and biogenic aerosols at >7.2 μm. OC and WSOC at 1.5–3.0 μm were likely to have been from the burning of yak dung and photochemical formation. The above results may draw attention in the public and scientific communities to the issues of air quality in the Tibetan Plateau.
摘要:
Radon, known to be a human carcinogen, is one of the most concerned radionuclides in uranium mining which need to be monitored and controlled. A large amount of radon is discharged to the atmosphere mainly through underground ventilation shafts for underground uranium mining. There are many studies on radon release of uranium mine, but the differences of the measured radon results are very big. In this paper, a typical underground uranium mine in China is chosen as a case study. This study finds that distribution of radon concentration and airflow speed inside the ventilation shaft are extremely uneven, but the distributions are respectively stable and regular for a fixed cross-section at the wellhead depth of 0-1m. There is also a stable numerical relationship between the radon release rate and the product of radon concentration and airflow speed at the center for any cross-section in the shaft. Based on this regulation, a multipoint interpolation-integration method and a one-point method for calculating radon release from underground ventilation shaft are proposed in this paper. The results show that the difference between these two methods is 2-10%, the one-point method is more suitable and convenient to be applied for the long-term monitoring radon release rate from uranium mine ventilation. The research results in this paper can be applied in the estimation of radon release rate for other underground uranium ventilation shafts.