不同能量加载条件下核材料放射性气溶胶特征分析

通过开展一系列不同爆炸能量加载条件下的核材料爆炸转化实验,结合放射性分析和化学分析等方法,得到爆炸后放射性气溶胶转化份额和粒径分布等重要信息。实验结果表明,爆炸产生的气溶胶粒子以中小粒径为主且粒度分布范围较广,其放射中位空气动力学直径主要集中在3.5~7.0μm之间,几何标准差介于3~4μm之间;炸药爆炸能量对核材料的气溶胶产生份额有着十分重要的影响,爆炸能量越大,对应气溶胶转化份额也越高。该项研究成果可为开展重大核材料爆炸事故场景下的放射性污染分布和人员受辐照危害评估提供重要的技术依据。     

铀自燃对放射性气溶胶的影响研究

以国内某金属铀真空蒸镀实验室的金属铀物料加工工艺为对象,采用放射性气溶胶连续监测,向心式气溶胶粒度分级采样,垂直高度分级采样等方法,研究了金属铀自燃对实验室空气中放射性气溶胶浓度、粒径分布、空间竖直分布的影响。结果表明,金属铀自燃明显提高了实验室空气中放射性气溶胶的浓度;所产生的气溶胶活度中位直径为9.89μm,粒径分布中大粒径气溶胶粒子占优;燃烧产生的放射性气溶胶在物料高度处浓度的增大水平高于工作人员呼吸带的增大水平。     

大气气溶胶中7Be的粒径分布

利用5级大流量串级撞击器采集大气气溶胶样品,高纯锗γ谱仪系统测量放射性,分析了大气气溶胶中放射性核素⁷Be的浓度及粒径分布规律。在样品采集期间,环境大气中⁷Be浓度平均值为7.29 mBq/m³,且在春季出现较大的浓度。研究发现,在粒径＞3.0 μm的气溶胶样品中,基本测量不到⁷Be;在粒径＞0.95 μm的气溶胶样品中,⁷Be仅占总量的10%左右;⁷Be主要分布在粒径＜0.95 μm的气溶胶粒子上。     

气溶胶采样技术简介(三)

五、各种粒度分级采样器介绍吸入有害气溶胶的剂量与其沉积部位有关,而沉积部位又与粒径有关。当危害正比于粒子质量时,剂量大小最好用不同粒径范围的质量浓度来估算,它可以用以下三种方法获得。1.对已收集的样品做粒度分布分析;2.对气载物质做粒度分析;3.在对气载物质的收集过程中就把其分成几个预计的区域沉积部分。在这些方法中,气溶胶粒子应按空气动力学直径分级,以消除由于粒子的形状和密度的不同而引起的差异。其分级方式     

凝聚式单分散气溶胶发生方法研究

自行设计建立了一套凝聚式单分散气溶胶发生实验装置。采用蒸发冷凝法,用不同浓度的NaCl溶液作为凝结核源,并分别采用DEHS(癸二酸二异辛酯)、DOP(邻苯二甲酸二辛酯)、PAO-4(聚癸烯,俗称金刚砂3004)作为试剂,进行了气溶胶的发生试验以及气溶胶性能测试。结果表明,严格控制各种影响气溶胶性能的参数,三种试剂均能发生出单分散气溶胶粒子(几何标准偏差σg≤1.25),粒径范围分别为DEHS(0.33～0.36μm)、DOP(0.35～0.37μm)、PAO-4(0.36～0.37μm),粒子数浓度均达到106粒/cm3以上。该装置产生的单分散气溶胶粒径特征和浓度基本符合高效粒子空气过滤器效率测试要求。     

220Rn子体气溶胶粒径分布测量的方法研究

应用ELPI系统、α谱仪和能量甄别法测量程序,建立了1套²²⁰Rn子体气溶胶活度粒径分布的测量方法;利用该方法收集了南华大学²²⁰Rn实验室不同粒径的²²⁰Rn子体气溶胶,并进行了²²⁰Rn子体气溶胶活度粒径分布测量。实验结果表明：ThB气溶胶的活度中位粒径(AMAD)平均值为237 nm,ThC气溶胶的AMAD平均值为245 nm。该方法简便易行、测量周期短,能实时得到²²⁰Rn子体气溶胶粒子数粒径分布的情况,能同时得到ThB和ThC气溶胶的活度粒径分布情况,且能谱法的测量精度也相对较高。     

安全壳过滤排放系统实验用气溶胶的确定及相关参数的选取

为了满足安全壳过滤排放系统的气溶胶过滤性能测试实验的要求,进行实验用气溶胶选取的方案研究。对安全壳内气溶胶实际特性进行计算评估,得出严重事故后安全壳内气溶胶的特性随时间的变化规律。综合考虑分析结果和国外的研究成果,确定实验用气溶胶为BaSO4、TiO2。实验用气溶胶的配送压力为0.1~0.65 MPa;主管道浓度为50~900 mg/m3,气溶胶质量中值直径为1μm,粒径分布的几何标准偏差为1~2。     

某污染区含钚再悬浮气溶胶的粒度特征

实验采集了某污染区的土壤和分级气溶胶样品,分析了其中239Pu的含量,研究了含钚再悬浮气溶胶的粒度特征,并结合土壤风蚀机理对核素再悬浮的过程进行了讨论。研究表明:在未扰动情况下,239Pu的活度中值空气动力学直径均值为3.1μm;在扰动情况下,大颗粒的浓度显著增加,而小颗粒中的239Pu的比例明显下降;239Pu的典型粒度分布样式基本符合文献提出的137Cs的部分粒度分布样式;再悬浮气溶胶中的239Pu的富集因子在0.002~0.2,与粒径的关系不显著。     

220Rn子体结合态放射性气溶胶粒径分布实验研究

放射性气溶胶粒径分布是评价环境中Rn、Tn子体所致呼吸道内照射剂量的重要参数.采用CR-39作探测器,ThB作示踪粒子,反推计算得到了Tn子体结合态气溶胶的中位径(CMD)和方差(GSD).在广东省阳江市(高本底地区)进行的现场测量结果表明,CMD分布为30～130 nm,GSD分布为1.9～3.3.与北京大学技术物理楼的实验结果相比较可知,潮湿的农村的CMD较小,且环境越潮湿,CMD一般会越小.另外,通风对气溶胶粒径的影响也很明显,砖房在通风状况好的情况下有较大的CMD.砖房的CMD普遍比水泥房间的小.     

秦山核电厂气态流出物气溶胶粒径分布测量

对秦山核电基地烟囱流出物的粒径分布谱进行了实验测量,结果表明:气态流出物中的气溶胶粒径大多在1 μm以下,但总粒子数浓度随机组类型不同而不同。测量结果为评估核电厂气态流出物监测系统采样的有效性提供了参考。     

A nanoparticle formation model considering layered motion based on an electrical explosion experiment with Al wires

To study the evolution of nanoparticles during Al wire electrical explosion, a nanoparticle formation model that considered layered motion was developed, and an experimental system was set up to carry out electrical explosion experiments using 0.1 mm and 0.2 mm Al wires. The characteristic parameters and evolution process during the formation of nanoparticles were calculated and analyzed. The results show that the maximum velocities of the innermost and outermost layers are about 1200 m·s−1 and 1600 m·s−1, and the velocity of the middle layer is about 1400 m·s−1, respectively. Most of the nanoparticles are formed in the temperature range of 2600 K‒2500 K. The characteristic temperature for the formation of Al nanoparticles is ∼2520 K, which is also the characteristic temperature of other parameters. The size distribution range of the formed nanoparticles is 18 to 110 nm, and most of them are around 22 nm. The variation of saturated vapor pressure determines the temperature distribution range of particle nucleation. There is a minimum critical diameter of particles (∼25 nm); particles smaller than the critical diameter can grow into larger particles during surface growth. Particle motion has an effect on the surface growth and aggregation process of particles, and also on the distribution area of larger-diameter particles. The simulation results are in good agreement with the experiments. We provide a method to estimate the size and distribution of nanoparticles, which is of great significance to understand the formation process of particles during the evolution of wire electrical explosion.     

核材料炸药化学爆炸条件下烟云源项的实验与仿真

为获取核材料化学爆炸事故烟云参数和气溶胶扩散规律,本文理论分析了核材料化学爆炸事故烟云扩散过程与机理,建立了基于CFD技术的烟云扩散数值仿真方法,并通过爆炸烟云外场扩散实验对该方法进行了验证。研究结果表明：CFD方法能实现烟云扩散的数值仿真;实验和仿真均显示小当量TNT爆炸高度远小于Church经验公式,宽度比例却增加;气溶胶颗粒在蘑菇云形态的双涡环烟云流场中分布不均匀,粒径大于50 μm的颗粒物大多位于烟柱中,而大部分可吸入颗粒物在烟云顶部聚集;气溶胶在烟云稳定前的驱散与沉降会改变其源项参数,以Operation Roller Coaster实验气溶胶积累质量分布为例的计算显示,空载释放率约为地面气化率的58%,可吸入比率由20%升高至31%,可吸入释放率约为18%。     

~(60)Co γ辐照制备钠米铜粉的研究

研究了60Co γ辐照硫酸铜水溶液体系制备纳米铜粉。用X射线衍射仪(XRD)、透射电子显微镜(TEM)、激光粒度仪分析(LSPSDA)和差示扫描量热仪(DSC)分别表征材料的结构、形貌、大小以及材料的熔点。结果表明,随着辐照剂量的逐步增加,辐照产物越接近纯铜,铜粒径逐渐减小,当辐照剂量达到400kGy时辐照产物为纯铜。不同辐照剂量对粒子的形貌没有影响,粒子主要呈球形。     

GISAXS and GIWAXS analysis of amorphous–nanocrystalline silicon thin films

Amorphous–nanocrystalline silicon thin films were deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) on glass substrate with various silicon nano-crystal size distributions and volume fractions. The samples were examined by Grazing Incidence Small Angle X-ray Scattering (GISAXS) and Grazing Incidence Wide Angle X-ray Scattering (GIWAXS) at the Austrian SAXS beamline (Synchrotron Elettra, Trieste) using an X-ray beam energy of 8 keV. The grazing incidence angle varied from the critical angle to 0.2° above the critical angle. This allowed the examination of the samples at different depths, and the distinction of the surface scattering contribution from the particles scattering in the bulk. The sizes of the “particles” obtained from the horizontal and vertical sections of 2D GISAXS patterns were between 2 nm and 6 nm. Since GISAXS is sensitive to electron density differences (contrast) between the scattering bodies and the surrounding matrix, it is not evident whether the particles are nano-crystals or just voids embedded in amorphous matrix. However, the size of the crystals calculated from the line-shape analysis of peaks in GIWAXS spectra and the crystal size distribution obtained from High-Resolution Transmission Electron Microscopy (HRTEM) images agree well with the size of “particles” estimated from GISAXS, strongly indicating that the observed particles are silicon nano-crystals.     

Characteristics of a plasma flow field produced by a metal array bridge foil explosion

To improve the energy utilization efficiency of metal bridge foil explosion, and increase the function range of plasmas, array bridge foil explosion experiments with different structures were performed. A Schlieren photographic measurement system with a double-pulse laser source was used to observe the flow field of a bridge foil explosion. The evolution laws of plasmas and shock waves generated by array bridge foil explosions of different structures were analyzed and compared. A multi-phase flow calculation model was established to simulate the electrical exploding process of a metal bridge foil. The plasma equation of state was determined by considering the effect of the changing number of particles and Coulomb interaction on the pressure and internal energy. The ionization degree of the plasma was calculated via the Saha–Eggert equation assuming conditions of local thermal equilibrium. The exploding process of array bridge foils was simulated, and the superposition processes of plasma beams were analyzed. The variation and distribution laws of the density, temperature, pressure, and other important parameters were obtained. The results show that the array bridge foil has a larger plasma jet diameter than the single bridge foil for an equal total area of the bridge foil. We also found that the temperature, pressure, and density of the plasma jet's center region sharply increase because of the superposition of plasma beams.     

Understanding the Mechanism of Nanoparticle Formation in a Wire Explosion Process by Adopting the Optical Emission Technique

In the present study nano-tungsten carbide particles were generated in a wire explosion process.The plasma generated during the wire explosion process was analyzed using optical emission spectroscopy(OES).The impact of ambient pressure on the plasma temperature,electron density and plasma lifetime was studied.Lifetime variations of the plasma produced under different experimental conditions were analyzed.The produced nanoparticles were characterized through wide angle X-ray diffraction(WAXD) and transmission electron microscopy(TEM) studies. Particles produced with a negative DC charging voltage had a larger mean size when compared to a positive charging voltage.Polarity dependence on the plasma duration was observed where plasma was sustained for a longer duration with a negative DC charging voltage.     

激光烧蚀铀材料生成铀微粒的形态学研究

本文以激光器作光源,利用激光的高温烧蚀特性,以激光束烧蚀金属铀和二氧化铀材料,模拟高温条件下形成铀微粒的过程,用扫描电子显微镜和透射电子显微镜对铀材料及产生的含铀微粒的形态学特点进行了表征。实验表明,在激光束的轰击下,两种靶材料均出现熔化现象,铀金属表面呈现明显波纹状结构,二氧化铀的表面轰击边缘处呈现趋球状物堆积。生成的铀氧化物微粒为μm级形态不规则微粒及1 μm左右的球形微粒,说明铀在高温过程中产生球形微粒。对比研究了来自高温爆炸过程的金属银微粒,进一步验证了高温高压过程会产生球形微粒。结果表明,密实的铀氧化物微球是铀材料参与高温化学过程的结果,与低温过程中的剥蚀作用有明显的差别,是高温化学过程的特征,这为高温高压环境中的微粒分析提供了参考依据。     

熔融物液柱碎化模型对先进压水堆堆外蒸汽爆炸计算的影响分析

在堆外蒸汽爆炸计算中,液柱碎化模型影响着熔融物液滴生成速率、液滴直径、液滴分布、液滴凝固和气泡比例等粗混合参数和现象,从而影响了蒸汽爆炸的冲击载荷。本文基于MC3D V3.8程序,采用不同的液柱碎化模型（CONST模型和KHF模型）对先进压水堆堆外蒸汽爆炸进行计算分析,探讨了CONST和KHF模型对蒸汽爆炸计算的影响。结果表明,两种模型计算的粗混合状态类似;在熔融物触底时刻,爆炸性准则几乎相同,此时触发爆炸得到的冲击载荷差别很小,表明该时刻触发爆炸时不同液柱碎化模型对爆炸冲击计算的影响较小;在本文所定义的工况下,先进压水堆堆坑墙体承受的最高压力约为20 MPa,最大冲量小于0.2 MPa•s。     

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。