一种用于SPM分析的大气气溶胶单颗粒样品的制备方法

介绍了一种用于扫描质子微探针分析的大气气溶胶单颗粒样品的制备方法。通过实验摸索出一种适合于支撑颗粒物的材料聚乙烯醇缩丁醛(PVB)。大气颗粒物被直接采集在PVB薄膜上从而制成样品,保持了颗粒物的原始信息。用显微镜观察了采集的颗粒物,颗粒物之间完全分开,颗粒物间距合适。样品的扫描质子微探针试验结果表明,所制成的单颗粒样品能经受住质子束的长久轰击。对PVB薄膜的本底测试表明,这种膜的本底很小,不会对被测颗粒物的元素产生干扰。     

上海市钢铁工业尘单颗粒分析

用高分辨率、高灵敏度的扫描质子微探针对上海市工业尘进行单颗粒分析,研究了在颗粒物中不同元素的分布以及元素平均含量随粒径大小的变化。结果表明,Fe、Cr、Mn等元素在颗粒物中均匀分布的,而K、Ca则富集在颗粒物的表面。而且这些元素的平均含量随粒径的变化呈现出一规律性,其中大部分重金属元素（如Cu、Cr、Ni、Zn、Pb）聚集在颗粒粒径＜5μm的颗粒物上。     

Identification of origin of single aerosol particles using polycapillary X-ray lens

A micro X-ray fluorescence (Micro-XRF) spectrometer based on a polycapillary focusing X-ray lens (PFXRL) and a laboratory X-ray source was designed to carry out the XRF analysis of single aerosol particles. The minimum detection limit (MDL) of this Micro-XRF spectrometer was 9 ppm for the Fe-Kα. The percentage of the particles of vehicle exhaust among aerosol particles was studied in Beijing, Chinese capital, during the test of odd-even driving restrictions for Beijing 2008 Olympics Games. This Micro-XRF spectrometer had potential applications in the analysis of single aerosol particles.     

基于扫描核探针技术的大气气溶胶单颗粒物源识别与解析方法研究与应用

将高分辨、高灵敏的扫描核探针(SNM)技术与人工神经网络(ANN)模式识别方法相结合,以单个气溶胶颗粒物化学表征为基础,开展大气气溶胶源识别与解析的新方法研究。摸索出单颗粒气溶胶SNM靶样的制备方法。建立了SNM多站多参量分析模式的数据获取系统和分析条件。用SNM测定了单个大气气溶胶粒子的元素谱特征。基于标准的误差反向传输神经网络算法,建立ANN模式识别系统,直接对单个气溶胶粒子的SNM分析能谱模式进行识别,判别其来源,计算源的贡献率。将建立的方法初步应用于上海市大气PM10源识别与解析研究。结果表明该方法解析能力强,解析结果客观,具有查找未知污染源、解析低浓度污染源的特点。     

Size-resolved source apportionment of aerosol particles using polycapillary X-ray lens with a plateau in its focal spot

A laboratory micro X-ray fluorescence spectrometer based on a special polycapillary X-ray lens (PXRL) was used to carry out the source apportionment of aerosol particles. In the curve of the distribution of the X-ray intensity in the focal spot of the special PXRL, there was a plateau with a diameter of 21.3 μm in which the distribution of the X-ray intensity was homogeneous. The gain in flux density in the plateau of the PXRL is 1490. The uniformity of this plateau was 2.9%. This was helpful for the quantitative X-ray fluorescence analysis of a single aerosol particle with smaller size than that of the plateau of the PXRL. The fingerprint database of aerosol particles with given sizes from various air pollution sources was established with the single particle analysis method. The size-resolved source apportionment of aerosol particles in haze in Beijing city was performed with this fingerprint database.     

基于Micro-PIXE能谱的大气单颗粒物污染源模式识别研究

来自不同排放源的大气气溶胶,其化学组成特别是微量元素组成具有各自的特征,在Micro-PIXE上呈现不同的特征峰。因此单个气溶胶颗粒物的Micro-PIXE能谱特征可作为其指纹,查找污染源。本文提出了适应于Micro-PIXE谱的模式识别算法,并对这种以Micro-PIXE能谱特征溯源的方法进行了可靠性检验。结果表明以此种方法进行源解析具有较高的可信度。相应的模式识别算法具有准确,快速的特点。     

严重事故下吸湿性气溶胶的自然去除研究

反应堆发生严重事故时,堆芯释放出的吸湿性气溶胶会在潮湿的安全壳内增大,从而影响其自然去除过程。本文理论推导了吸湿性气溶胶的增大模型并通过多种方法对其进行了验证。模型计算结果表明,气溶胶的增大过程由于受到溶解度的限制而存在临界湿度值,在该临界值以下时气溶胶不发生吸湿,但这未被其他严重事故分析程序所考虑。同时,基于某三代先进压水堆的特定严重事故工况,本文分析了干颗粒半径及湿度对气溶胶的平衡半径和自然去除系数的影响。结果表明:气溶胶的自然去除系数随干颗粒半径的增大将先减小后增加,并在1 μm时达到最小值;相同湿度下,干颗粒半径对气溶胶半径的最大增大比例的影响不大;湿度的增加对不同干颗粒半径气溶胶去除系数的影响不同。      

Molecular dynamics simulations of laser disintegration of amorphous aerosol particles with spatially nonuniform absorption

A series of molecular dynamics (MD) simulations are performed in order to provide qualitative information on the mechanisms of disintegration of aerosol particles as used in aerosol mass spectrometry. Three generic types of aerosol particles are considered: strongly absorbing particles with homogeneous composition, transparent particles with absorbing inclusion, and absorbing particles with transparent inclusion. To study the effect of the mechanical properties of the aerosol material on the disintegration process, the results for crystalline (brittle) and amorphous (ductile) particles are compared. For large laser fluences, nearly complete dissociation of the absorbing material is observed, whereas the nonabsorbing portions remain fairly intact. Because large fluences can cause photofragmentation of constituent molecules, multiple pulses at low laser fluence and/or lasers with different wavelengths are recommended for the best representative sampling of multicomponent aerosol particles in laser desorption/ionization (LDI) mass spectrometry.     

Study of emission episodes of urban aerosols by ion beam analytical techniques

The quantitative elemental composition and morphology of over 500 atmospheric aerosol particles were determined by nuclear microscopy and scanning electron microscopy (SEM). The samples originated from eight sampling campaigns, when hourly variation and sources of the urban aerosol elemental components were studied in Debrecen between 2007 and 2010. Aerosol which could be connected to heavy metal pollution episodes and high aerosol pollution levels deposits were selected for the nuclear microprobe study.Ion beam analytical methods (micro-PIXE and STIM) provided the elemental composition of coarse (particles with aerodynamic diameter between 2.5 and 10 μm) aerosols while the morphology of the different particle types was determined by SEM.Through the elemental composition, elemental correlations and morphology different particle types were identified and attributed to different anthropogenic sources like biomass burning, oil combustion, traffic or industry.     

负载型多分散气溶胶在管道内的传输规律

放射性气溶胶的传输一直是倍受关注的环境问题。为研究放射性气溶胶在管道内的传输规律,首先自制了能够产生稳定的、多分散气溶胶的发生器。主要考察了稀释气流速（5~25 L/min）、气溶胶颗粒粒径（多分散体系）及固体颗粒密度（土壤、石英砂）对气溶胶在管道内传输的影响。即考察了粒径多分散的石英砂、土壤颗粒形成的气溶胶及表面负载Ag的石英砂颗粒模拟负载型放射性气溶胶,在不同稀释气流速作用下进入管道内的传输,针对每一节管道内的沉积物进行收集分析,从而得到气溶胶在管道内的传输及沉降规律。研究结果表明：密闭管道内,在一定流速范围内,沉积物最高频度粒径随着管道距离的增长而先增大后减小;小粒径的颗粒在传输过程中自重沉降,且由于布朗运动吸附在大粒径颗粒物表面加速其沉降速率,即减小了其在管道内的传输距离;表面负载Ag的石英砂颗粒形成的气溶胶随着稀释气吹扫导致Ag和石英砂颗粒之间有不同程度的分凝,气流速率越大,分凝现象越明显。     

通排风系统中239PuO2气溶胶微粒的流动特性

运用计算流体动力学(CFD)方法模拟研究了事故状态下有人员工作时,²³⁹PuO₂微粒在不同工况下的流动特性及其粒子轨迹。结果表明：工作间关门,有利于放射性气溶胶微粒及时从排风口排出。研究结果对工作人员在事故条件下规避放射性气溶胶的危害提供了重要的参考。     

Study of individual atmospheric aerosol particles at the Debrecen ion microprobe

Aerosol samples collected in outside and indoor environments with a 9-stage PI cascade impactor were analysed using PIXE, STIM (on and off-axis) and RBS ion beam analytical techniques at the Debrecen ion microprobe. Elemental composition, size and morphology of single aerosol particles were determined.Since the quantitative determination of light element concentrations requires a support material with small or no light element content, impactor surfaces made of different materials were tested in order to optimize the sampling and analysis. Thin polymer and Al foils were found to be possibly adequate substrate materials.     

MAPPIX: A software package for off-line micro-pixe single particle aerosol analysis

In the framework of a multiannual experiment performed at Baia Terra Nova, Antarctica, size-segregated aerosol samples were collected by using a 12-stage SDI impactor (Hillamo design). Approximately 2800 particles, belonging to the first four supermicrometric SDI stages – 8.39, 4.08, 2.68, 1.66 μm dynamic aerosol diameter cuts – were analyzed at the INFN-LNL micro-PIXE facility, a three lens Oxford Microprobe (OM) product, installed in the early nineties. Four regions on each of the 12 sub-samples were measured; 60 aerosol particles were detected on average in each of the analyzed regions.The off-line single aerosol particle (SAP) analysis of such big amount of data required software that is able to rapidly handle the acquired data, with a simple and fast area selection procedure; the subsequent automated PIXE spectra analysis with a specialized code was also needed.The MAPPIX 2.0 software was designed to make easier and faster the user jobs during the SAP analysis. The package is composed of two separate routines: the first one is devoted to data format conversion (OM-LMF file format to MAPPIX format), while the second one is devoted to micro-PIXE maps graphical presentation and aerosol particle selection procedure.The MAPPIX data format and software features will be discussed; a short report of the speed performances will be presented.     

State of development of the computer programme BACCHUS-3D/TP for the description of transient two-phase flow conditions in LMFBR fuel pin bundles

The three-dimensional transient two-phase flow version of the computer programme BACCHUS-3D/TP (Two Phase) relies upon the basis supplied by the single phase flow version of the code. The bundle geometry typical of LMFBRs is modeled by means of the porous body approach based on the concepts of volume porosities, surface permeabilities, distributed resistances and heat sources. Two phase flow is described by means of two physical models available in two distinct versions of the code. One of these two-phase models is a three-equations Slip Model (SM) which provides as a subcase the Homogeneous Equilibrium Model (HEM) if no slip between the phases is assumed. The second is a six equation model referred to as Separated Phases Model (SPM) in which two coupled systems of governing equations are solved for the vapour and liquid phases.

A fully implicit treatment of the conservation equations for the coolant flow is followed in the SM and a half-implicit approach in the SPM. The article outlines the present state of the code development and future activities aiming at unifying both variants in a comprehensive code version describing the transition between different two-phase flow regimes from bubbly flow to dispersed annular flow. An assessment of the present capabilities of the code has been made with the theoretical interpretation of out-of-pile sodium boiling experiments in a 7- and 37-pin bundle. Numerical results are discussed and compared with experimental data.     

爆轰条件下的气溶胶粒径分布及Ag质量分数与粒径的关系

用货币银化爆实验研究了爆轰条件下气溶胶生成量及粒径分布规律.实验结果表明,爆炸后气溶胶粒子粒度分布的变化,主要取决于布朗凝并以及重力沉降相结合的过程,相对稳定气相中的气溶胶粒度主要分布在1.8μm左右;用中子活化法分析不同粒径的气溶胶粒子中Ag的质量分数,结果表明,Ag存在着明显的分凝效应;经过SEM和XRD方法分析,10μm以下的Ag气溶胶粒子多以由较小的多晶聚合体逐级凝并成较大的聚合体结构存在,平均晶粒尺寸为27.3nm.     

Calibration of Cascade Impactor by Two-Stage Method

A simple method of calibrating the cascade impactor has been developed by applying Hongo et al.'s two-stage method to evaluate the particle-size distribution. The constants ψ and σfor a function representing the impaction efficiency were determined for the UNICO cascade impactor, using the test particles produced by a spinning-disc aerosol generator. The values were ψ=0.35, σ=1.46, respectively.

The validity of the method for the UNICO cascade impactor was confirmed from microphotographic observation of a sample artificial aerosol containing different sizes of uranine methylene-blue particles. Both the mass median aerodynamic diameter and the geometric standard deviation obtained with the method agreed with the microphotographie measurements with relative errors not exceeding 10%.     

AHMED experiments on hygroscopic and inert aerosol behaviour in LWR containment conditions: experimental results

Hygroscopic NaOH, CsI, CsOH and inert Ag aerosol behaviour at different temperatures and relative humidities (RH) has been studied in a well instrumented and controlled vessel of 1.81 m³ total free volume. Homogeneous thermal-hydraulic conditions for aerosol measurement in the vessel were achieved. The aerosol number and mass concentration were measured continuously during the experiments using a Condensation Nucleus Counter and a Tapered Element Oscillating Microbalance. The particle size distribution and chemical composition in the test conditions were measured by Berner low pressure impactors. In the case of NaOH the half life of the aerosol mass concentration was more than four times longer at low RH (22%) as compared to high RH (96%). The half lives of the CsOH and CsI aerosols were only twice as long at low RH as compared to high RH. Thus at high RH (96–97%) the half lives of CsOH and CsI were twice as long as the half life for the NaOH aerosol. The faster decay of the NaOH aerosol is due to the smaller density decrease of NaOH during water condensation. CsOH particles grew rapidly to their equilibrium size at all humidities. The measured equilibrium size for CsOH aerosol agree well with the calculated particle size at different RHs. Experimental results were also compared with calculations obtained by severe accident computer codes. These calculated results will be presented in a later paper.     

The aerosol release factor for Pu as a consequence of an ion exchange resin fire in the process cell of a fuel reprocessing plant

One of the upper limit accidents usually considered in the safety analysis of a fuel reprocessing plant is an accidental explosion, followed by a fire, of an ion exchange column containing resin loaded with large quantities of plutonium. In such accidents, a certain fraction (release factor) of Pu is released in the form of an aerosol into the ventilation system, and finally to the environment through HEPA filters and the stack. The present study was undertaken to determine the aerosol release factor for Pu in the process cell of a typical fuel reprocessing plant.Geometrically similar scaled-down models of three different sizes were built, and suitably scaled-down quantities of resin loaded with thorium in nitric acid medium were burnt in these model cells. Thorium was used in place of Pu because of its physical and chemical similarities with Pu. The release factor was obtained by comparing the amount of Th in air with the total. The study also dealt with aerosol characteristics and kinematics of process of fire.The aerosol release factors for the three models were found to lie in the range 0.01–0.07%, and varied non-monotonically with model size. The analysis of scaled down results in conjunction with simplified aerosol modelling yielded the release factor for the actual cell conditions as 0.012% with an upper limit value of 0.1%. The particle size analysis based on Th-radioactivity and particle-mass indicated nonuniform tagging of Th to aerosol particles. These particles were irregularly shaped, but not as long chain-like aggregates.The study proposes, with a reasonable degree of conservatism, the release factor of 0.1% for such fires, and aerosol parameters, AMAD and σ_g, as 2 μm and 2 respectively. However, for situations significantly different from the present one, the release factor of 1% recommended by the American National Standards Institute may be used with a greater degree of confidence in the light of the present work.     

全陶瓷微密封燃料有效多群截面计算方法研究

全陶瓷微密封（FCM）燃料是一种弥散颗粒燃料。由于弥散颗粒燃料存在双重非均匀性,传统的确定论方法及蒙特卡罗方法皆难以处理这种双重非均匀效应以获得有效多群截面。本文基于超细群方法建立FCM燃料的有效多群截面计算方法。为描述燃料棒内TRISO颗粒的非均匀性,在共振能量段,通过采用超细群方法求解包含TRISO颗粒的一维球模型得到超细群缺陷因子,通过超细群缺陷因子修正所有核素的超细群截面即可将颗粒和基质均匀化。由于TRISO颗粒在热能区也存在较强的自屏效应,在热能区,利用穿透概率及碰撞概率等价得到多群缺陷因子,通过多群缺陷因子修正所有核素的多群截面将燃料和基质均匀化。均匀化后的FCM燃料组件即可视为普通压水堆燃料组件进行共振计算。利用丹可夫修正因子等价得到FCM燃料组件各燃料棒的等效一维棒模型,对一维棒模型求解超细群慢化方程从而得到共振能量段的有效自屏截面。数值结果表明,该方法能有效处理FCM燃料的双重非均匀性,得到精确的有效自屏截面。     

Source apportionment of single aerosol particles in the atmosphere of Shanghai city

A nuclear microprobe with high spatial resolution and high analytical sensitivity was applied to analyze atmospheric aerosol at five monitoring sites in Shanghai city.Meantime,a new pattern recognition technique,which used the micro-PIXE spectrum of a single aerosol particle as its fingerprint.was developed to identify the origin of the particle.The results showed that the major contributors to the atmosphere pollution were soil dust(31.6%) ,building dust(30.8%),and the next were vehicle exhaust(13.7%),metallurgic industry excrements(5.6%).oil combustion(5%) and coal combustion(2.3%).Besides these ,about 10% of the particles could not be identified.Based on the cluster analysis of these particles.they could be divided into eight groups.By inference,they might belong to some sub-pollution sources from soil dust,building dust and metallurgic industry excrements.Moreover,some new pollution sources from tyres and chemical plants were also revealed.