大气颗粒物滞留时间的确定方法及初步实验验证

通过研究大气颗粒物中222Rn子体活度比与颗粒物平均寿命之间的关系,建立了基于活度比估算大气颗粒物滞留时间(residence time of atmospheric aerosol,RTAA)的方法,并在相对理想条件下进行了实验验证.当氡室浓度稳定为1.816kBq/m3时,由214Bi/214Pb活度比计算出的RTAA为112.17min,与氡室的平均换气时间(104.17min)相当,表明大气颗粒物中同一衰变链上的放射性核素活度比(如214Bi/214Pb,210Bi/210Pb或210Po/210Pb)可以用于估算RTAA.     

基于激光雷达探测技术的PM2.5浓度辨识研究

针对颗粒物浓度的大气分布难以测量的问题,采用532 nm激光雷达,对淮南地区2016年6月1日至12月31日进行连续观测。利用大气边界层高度、气溶胶光学厚度、温度、相对湿度、风速、能见度和实测的颗粒物浓度建立回归预测模型,实现了对颗粒物浓度的辨识研究。由于传统的反向传播(BP)神经网络易陷入局部极小,依据数据特点采用基于遗传算法的反向传播(GA-BP)神经网络进行研究,利用遗传算法寻找最优的权值和阈值,以平衡全局与局部的矛盾。通过两个回归模型的比较,可知GA-BP方法明显优于BP方法,BP方法的测试集的相关指数R~2是0.623,平均预测误差是24.692μg/m~3;GA-BP方法的测试集的相关指数R~2是0.899,平均预测误差是7.122μg/m~3。由此说明激光雷达可以有效地监测大气颗粒物的分布,并为淮南地区的颗粒物监测提供数据支持和参考依据。     

基于β-X射线分析技术的大气颗粒物浓度-元素分析仪研制

针对城市大气颗粒物监测、污染物溯源等工作现场实时分析的迫切需要,研制了基于β-X射线分析技术的大气颗粒物浓度-元素分析仪。以β射线在物质中的衰减规律和能量色散X射线荧光分析原理,通过仪器总体设计、结构设计、FPGA硬件电路设计和软件设计,实现了在线分析大气颗粒物浓度及其元素识别、含量计算等功能;通过制备纯元素颗粒沉积滤膜样品作为大气颗粒物标准样品,完成了分析仪的标定。该分析仪可在线、连续监测大气颗粒物(如TSP,PM₁₀,PM_2.5)的质量浓度及其所含的30种元素种类和含量。成都东郊的现场应用显示,分析仪对大气颗粒物的浓度测量值与成都环保局的监测值具有很好的一致性,对颗粒物中所含重金属元素(如As,Hg,Cd,Cr,Pb等)的监测较为灵敏。通过技术性能测试,表明分析仪具备检出限低、快速分析、使用方便等特点,能够满足城市大气监测过程中对颗粒物浓度和元素实时分析的迫切需求,具有较强的现场应用能力。     

基于太阳光度计测量确定分层大气消光系数

太阳光度计是地基探测整层大气光学参数的重要仪器,而在一些研究与工程应用中更需要了解低层大气光学参数。基于均匀平行球面大气分层的假定,提出了利用太阳光度计测量的数据确定分层大气平均消光系数的算法。应用该算法处理POM-02太阳光度计的实际测量数据,研究表明这种分层算法得到的大气总光学厚度与整层算法得到的大气总光学厚度的相对误差小于3%。利用该分层算法求得的低层大气平均消光系数与激光雷达测量的消光系数进行比较,两者具有较好的一致性。因此,这种利用太阳光度计测量数据确定分层大气平均消光系数的算法是可行的,该算法拓展了太阳光度计的应用。     

激光雷达监测工业污染源颗粒物输送通量

PM10指能进入呼吸道的质量中值直径小于等于10μm的颗粒物,它是反应环境质量的重要指标,大气中过多的PM10会严重危害身体健康。激光雷达可以测量大气颗粒物消光系数,近地面颗粒物消光系数与颗粒物质量浓度是相关的,利用震荡天平(TEOM)测量近地面的PM10质量浓度,与雷达测量的消光系数建立经验关系,可以推算PM10质量浓度的垂直分布。风廓线雷达可以获得不同高度上的风向风速,将PM10质量浓度与风场数据二者结合可以计算不同高度上颗粒物向城区的输送通量,最终可以估算污染源向城区的输送总量。使用激光雷达技术对北京重要工业污染源进行了长时间的连续监测,获取了颗粒物输送通量等多种参数,给出了连续监测结果。     

高功率微波作用下O-离子解吸附产生种子电子过程

种子电子是高功率微波大气击穿的根源, 研究高功率微波大气击穿时, 一般假设背景大气中存在种子电子, 此假设在低层大气环境中会给模拟结果带来较大误差. 本文建立了高功率微波强电场作用下O^-离子解吸附碰撞过程物理模型, 基于传统的空碰撞模型, 提出了改进的蒙特卡罗仿真方法, 编写了三维仿真程序, 对高功率微波作用下O^-离子的解吸附过程进行了仿真, 分析了O^-离子平均能量随时间的变化过程以及O^-离子与空气分子的碰撞过程, 得到了不同压强、场强、频率和击穿体积条件下种子电子平均产生时间. 理论与仿真结果表明, 随着频率增大, 种子电子平均产生时间变大, 随着击穿体积、场强以及压强增大, 种子电子平均产生时间变小. 最后, 考虑O^-离子与空气分子解吸附碰撞提供种子电子条件下, 给出了大气击穿时间理论与实验对比结果, 发现高功率微波频率较低时, 该种子电子产生机理可以解释实验结果, 而高功率微波频率较高时, 该机理下种子电子平均产生时间过长而与实验数据不符.     

大气颗粒物成分分析标准物质研究进展与思路

颗粒物已成为一些城市大气的首要污染物。由于准确测定大气颗粒物的化学组成难度大、技术要求高，为了确保测量结果的准确度和溯源性，需要与之相近的标准物质。从大气颗粒物标准物质候选物来源组成、样品采集、制备技术、特性量组分与分析技术等方面，梳理了国内外相关研究进展。分析了我国大气颗粒物标准物质存在的基体类型少、采样制备技术落后、样品短缺等问题。结合国外大气颗粒物标准物质研究经验，以我国生态环境监测与治理修复重大需求为导向，从标准物质的代表性和实用性角度出发，探索切实可行的研究思路。创新性提出基于大气可吸入颗粒物质组成和来源解析，针对性采集研究区内各种主要源物质，根据基体和含量特征要求，通过对源物质的组合制备，获得一系列目标含量候选物样品的方法。     

原位红外光谱法研究大气颗粒物表面非均相反应

大气污染物之间可能发生协同作用,造成严重的二次污染,产生次生环境问题.本实验通过原位红外光谱分析方法研究气态污染物和碳颗粒物之间的吸附过程,发现大气中CO2和NO极易在颗粒物表面发生吸附;CO2在颗粒物表面达到吸附平衡时间很短,NO的吸附平衡时间较长;CO2和SO2会影响NO在颗粒物表面的吸附,CO2在颗粒物表面的吸附几乎不受NO和SO2的影响.     

基于主动差分吸收光谱系统获取大气颗粒物光学特性研究

以主动差分吸收光谱遥感技术为基础,在干净大气环境条件下,结合参考光路设计技术,开展了获取近地面气溶胶颗粒物的光谱新方法研究.针对以宽带氙弧灯为光源的主动差分吸收光谱系统固有宽波段特性,建立了解析颗粒物光学厚度模型,获取了大气颗粒物光学特性.最后通过外场实验,获得测量期间气溶胶颗粒物光学厚度,然后采用对数线性回归获取Angstrom波长指数和混浊系数,以及大气能见度数据.主动差分吸收光谱系统用测量光程范围内的大气总的吸收特性,获得监测区域的颗粒物平均水平,更具有代表性和进一步应用价值.     

多光子反Jaynes-Cummings模型中混合态二能级原子的粒子数反转特性

利用多光子反Jaynes-Cummings模型研究了单模相干光场与混合态二能级原子相互作用时,二能级原子的粒子数反转特性.讨论了相干光场的平均光子数、跃迁光子数以及原子初始态的混合度等参量对粒子数反转的影响.结果表明：二能级原子的粒子数反转有周期性的崩塌和回复现象. 相干光场平均光子数和跃迁光子数的增加会改变原子的回复周期和崩塌的衰减时间;随相干光场平均光子数的增加粒子数反转的振荡频率增大;随着混合度的减少回复的周期性和崩塌的衰减时间不发生变化但粒子数反转的振荡幅度增大.     

System for calibration of track detectors used in gaseous and solid alpha radionuclides monitoring

A laboratory system for the calibration of track detectors and charcoal detectors used in monitoring of radon and its decay products/their aerosols in air, is proposed. The system consists of three main components: (i) the alpha exposure chambers, including alpha monitoring devices and the connection with the ²²⁶Ra radioactive source. The CR-39 track detectors are mounted in the monitoring devices pre-equipped or not with paper filter; (ii) the calibrated  ²²⁶Ra source. Among the three tested sources: ²²²Rn, ²²⁶Ra+²²²Rn and ²²⁶Ra, the ²²⁶Ra source is considered the most appropriate radon source for our calibration system. It is kept into an airtight flat bottom flask, the radionuclide ²²⁶Ra being always in the radioactive equilibrium with their descendants. In the alpha exposure chambers, the source assures the radon at a constant rate; (iii) the ALFAUURASE program for the computation of radioactive accumulation of the alpha ²²⁶Ra descendants. For any initial mass of the parent, the amount and the activity of each alpha decay product and of all the decay products can be calculated by this computation program. Each component of the calibration system is described in the paper. The use of the system for the calibration of CR-39 track detectors in radon measurements is tested.     

Radon decay products attached to clothes in a nuclear laboratory

A whole body counter determined the presence of radioactivities up to 21.8 kBq for ²¹⁴Bi and up to 18.7 kBq for ²¹⁴Pb attached to clothes of workers in a Nuclear Research Laboratory. A radon survey reveals that 80% of the monitoring areas have radon concentration values lower than 500 Bq m⁻³, while 10% of the sampling points with values bigger than 1 kBq m⁻³ correspond to the workers mentioned above. By exposing samples of 0.04 m² clothes in a radon chamber, it was observed that radon decay products ²¹⁴Bi and ²¹⁴Pb were attached to them with an activity of 315–618 Bq per each kBq m⁻³ of Rn concentration additionally, fibres characterised with a lower electrostatics build up showed the lower attachment.     

The use of track registration detectors to reconstruct contemporary and historical airborne radon (RN) and radon progeny concentrations for radon-lung cancer epidemiologic study

Epidemiologic studies that investigate the relationship between radon and lung cancer require accurate estimates for the long-term average concentrations of radon progeny in dwellings. Year-to-year and home-to-home variations of radon in domestic environments pose serious difficulties for reconstructing an individual's long-term radon-related exposure. The use of contemporary radon gas concentrations as a surrogate for radon-related dose introduces additional uncertainty in dose assessment. Studies of glass exposed in radon chambers and in a home show that radon progeny deposited on, and implanted in, glass hold promise for reconstructing past radon concentrations in a variety of atmospheres. We developed an inexpensive track registration detector for the Iowa Radon Lung Cancer Study (IRLCS) that simultaneously measures contemporary airborne radon concentrations, surface deposited alpha activity density, and implanted ²¹⁰Po activity density. The implanted activity is used to reconstruct the cumulative radon and radon progeny exposure from the age of the glass and the ratios of the contemporary deposited activiteis to airborne radon gas activity. We placed over 2500 of these detectors in more than 1000 homes and retrieved 97% of them after a one-year exposure period. A preliminary analysis of the 1280 detectors that have undergone quality assurance review shows that the modules are meeting their accuracy and precision goals (10%). There is good correlation (r²0.5) between the total radon exposure estimated from contemporary radon gas measurements and historical average reconstructed from the implanted ²¹⁰Po surface activity. The linear regression slope of the airborne radon exposure to implanted activity is the same as the room model slope based on typical room parameters. This correlation improves (r²0.7) when the deposited surface activity measurements are added to the linear regression. Thus, track-registration detectors can contribute to accurate radon-related dose assessment in epidemiologic studies. Additional work is planned to incorporate the deposited activities in a more sophisticated reconstruction model.     

利用强流ISOL束研究20Na的奇异衰变模式(英文)

北京放射性离子束装置（Beijing Radioactive Ion-beam Facility,BRIF）是基于在线同位素分离器技术的国家大科学平台。在BRIF装置上利用100 MeV的质子束轰击较厚的反应靶产生放射性核素;反应产物经离子源电离和在线分离,在线同位素分离段可引出100~300 keV的放射性核束,质量分辨率达20 000。在基金委科学仪器基础研究专项的支持下,建成了多用途的衰变实验终端,包括束流传输管道、通用靶室、带电粒子和γ探测器、集成电子学和数据获取系统等。利用100 MeV的质子束轰击MgO厚靶产生了流强高达1×105 pps的20Na放射性核束。通过高效率地同时测量β,γ和α,第一次直接观测到20Na非常稀有的β-γ-α衰变模式。Beijing Radioactive Ion-beam Facility(BRIF) has been commissioned as the national Radioactive Ion Beam(RIB) facility based on the Isotope Separator On Line(ISOL) technique since 2016. At BRIF, the radioactive nuclides are produced by the proton beam of 100 MeV bombarding a thick-target, the reaction products diffusing out of the target are ionized by an ion source and delivered to the online mass separator. In addition to the post-accelerated radioactive ion beams, BRIF can provide low-energy ISOL beams of 100 to 300 keV with a mass resolution of 20 000. A general-purpose decay station has been built including the ISOL beam transport line, a conventional reaction chamber, charge-particle and γ detectors with integrated electronics and data acquisition system. An intense 20Na ISOL beam up to 1×105 pps was produced by using the 100 MeV proton beam bombarding a MgO thick target. With high-efficiency measurements of β, γ and α simultaneously, very rare β-γ-α decay mode in 20Na has been directly observed for the first time in the present work.     

全剥离离子94mRu44+的衰变研究

在兰州重离子加速器冷却储存环（HIRFL-CSR）上,用等时性质量谱仪首次研究了百微秒量级全剥离离子94mRu44+的衰变。94mRu44+由初级束流112Sn轰击Be靶产生,经过放射性束流线RIBLL2的筛选后注入到等时性设置的实验环CSRe中,并利用安装在实验环中的飞行时间探测器测量离子在CSRe中的循环周期。94mRu44+退激引起的质量改变会带来其循环周期的变化,由此直接观测到了94mRu44+退激到基态的过程。确定了本次实验中衰变事例探测的灵敏区间,并讨论了衰变发生时刻的测量精度。同时,测量了短寿命核素94mRu44+的质量,其半衰期约为100 μs,这是目前储存环质量谱仪测量的最短寿命核素的质量。The decay of the fully stripped ion 94mRu44+ in the order of one hundred microseconds has been studied for the first time by using the Isochronous Mass Spectrometry (IMS) at the HIRFL-CSR facility in Lanzhou. 94mRu44+ was produced via projectile fragmentation of a 112Sn primary beam bombarding on a 9Be production target. After the in-flight separation with RIBLL2, the ions were injected into the experimental ring (CSRe) and then stored there. The revolution times of the stored ions were measured by a Time-of-Flight (TOF) detector. Due to the mass change of a 94mRu44+ ion caused by its de-excitation to the ground state, hence the revolution time change, the decay process of 94mRu44+ could be directly observed in the CSRe. The sensitive window for detection of the decay events and the measurement precision of the decay time have been determined in this work. At the same time, we measured the mass of short-lived 94mRu44+ with the half-life about one hundred microseconds, which is the shortest among nuclides that have been studied by using storage-ring mass-spectrometry.     

通过惰性气体氙判断核试验信息的方法

全面禁止核试验条约的达成是防止核武器扩散的重要手段. 如何判断一次核试验的发生是一个关键课题. 研究了基于测量惰性气体氙同位素^133mXe,¹³³Xe,¹³⁵Xe和^131mXe来鉴别核试验和民用反应堆泄漏的方法. 通过分析这些处于复杂衰变链上核素的数量随时间的变化,寻找核试验与反应堆泄露事件的区别. 对两次朝鲜可疑的事件进行了测量和分析. 为了验证理论计算结果,设计了一次热中子辐照钚的模拟实验. 关键词： 全面禁止核试验条约核查 气体裂变产物 核试验判据 惰性气体氙核素     

Environmental gamma and radon dosimetry in Venezuela

Environmental gamma exposure and radon concentration levels measured in Venezuelan regions are presented. A new generation image analyser was used for particle track counting in CR-39 detectors. Mineral water wells from where water is supplied for massive consumption have an alpha activity around 0.450 Bq L⁻¹ and few of them have concentrations above 50 Bq L⁻¹. Coastal potable water activity is on the average around 5.3 ± 12% Bq L⁻¹. Indoor radon national average is 36 ± 5% Bq m⁻³; in two of the 36 monitored sites, the measured average is above 400 ± 5% Bq m⁻³. In air gamma dose values are between 100 and 144 nGy h⁻¹. In soil, ¹³⁷Cs concentration is around 0.5 and 10 Bq kg⁻¹ at the depth of down to 20 cm. Building materials were included in this study. ⁷Be and ¹³⁷Cs were measured in low concentration in tropical plants on Tepuy-s (sacred mountains in the Amazonas State). Geological active faults were identified by radon concentration measurements using LR-115.     

Comparison of radon exposure assessment results: Po surface activity on glass objects vs. contemporary air radon concentration

Radon exposure assessment in case–control studies on radon and lung cancer is generally based on contemporary radon concentration measurements, which can be affected by significant changes in the building structures or in living habits. Another method to estimate the radon exposure of the subjects is the recently developed retrospective dosimetry technique based on the ²¹⁰Po surface activity from glass objects. In order to compare the results obtained by the two methods, a study has been carried out in a sample of 26 dwellings in Rome, with radon concentration values ranging from 28 to 623 Bqm⁻³. Retrospective detectors based on CR-39 and LR 115 were exposed on 50 glass objects in bedrooms and living rooms. The correlation factor between the two sets of data, after removing six extreme values, is 0.67, which is similar to results obtained in other validation studies of similar sample size. The correlation increases to 0.83 if the 21 objects exposed in non-smoky dwellings are selected, while it vanishes to −0.01 for the 23 objects exposed in smoky dwellings, suggesting quite larger variations of plate-out in presence of environmental tobacco smoke.