参加IAEA能力验证项目的经验和体会

介绍2004—2011年间中国辐射防护研究院分析测试中心(以下简称本实验室)参加的IAEA组织的5次放射性分析能力验证项目,分析了5种介质的26个能力验证样品,项目共要求报出数据114个,本实验室报出了107个,7个数据未报。所报出数据的通过率为90%,10%未通过。7个未报数据样品包括水中226Ra、石膏中230Th、土壤中241Am和238Pu。已报出数据未通过的包括水中234U、238U和133Ba,土壤中210Pb、208Tl、210Po和奶粉中109Cd。分析未通过的原因主要有3个,第一是当时缺少必要的化学示踪剂,因此无法保证测量准确度;第二是有些项目缺少成熟的方法,有的正在建立;第三个原因是低能γ谱分析水平有待提高。     

γ能谱法分析放射性核素时对γ射线全能峰干扰的修正

针对在中核集团公司核电厂和“两厂两院”环境监测实验室比对中γ能谱分析存在的γ射线全能峰干扰问题,开展土壤中铀、钍、镭、钾、铯等γ核素测量实验。天然土壤标准源对谱仪进行效率刻度时,分析γ射线特征峰是否受到其它射线干扰,对受到干扰的γ射线通过修正代入效率计算的核素活度值以实现效率的拟合。由谱仪分析软件分析样品核素活度时,当利用不同特征γ射线计算的核素活度相差较大时,应进行活度修正。分析用于核素活度计算的γ特征峰(如²³⁵U 185.7 keV,²³⁸U 92.6 keV)受到的干扰峰,计算干扰峰对测量能谱峰(重峰)活度贡献,扣除干扰峰活度,即为γ特征峰贡献,由此给出样品核素活度值。这种方法在中核集团土壤样品比对中报出的²³⁸U、²²⁶Ra、²³²Th、⁴⁰K和¹³⁷Cs数据全部合格。     

国际原子能机构γ能谱测量比对

介绍了参加国际原子能机构(IAEA)组织的全球实验室间样品能力验证概况。分析连云港辐射环境监测管理站近3年(2020～2022年)运用无源效率刻度方法分析IAEA样品,模拟出水样、生物、滤膜不同介质的效率曲线,分析样品中⁴⁰K、⁶⁰Co、⁷⁵Se、^110mAg、¹³⁴Cs、¹³⁷Cs、²⁴¹Am等核素的浓度,报送34个数据的准确度和精密度均满足IAEA评估要求。验证无源效率刻度方法分析IAEA样品的实用性和可靠性,为该方法在环境辐射监测中的推广应用提供依据。     

FL-PFS法快速识别γ谱中低计数率核素

探讨了一种基于模糊逻辑与概率因子迭加算法识别γ谱中低计数率核素的分析方法。对²⁴¹Am、¹³³Ba、¹³⁷Cs、⁶⁰Co、¹⁵²Eu五种核素不同测试时长的多核素实测谱进行测试。结果表明,本算法随着迭加次数的增加,核素识别率迅速上升。概率因子迭加次数达到15次以上时,核素识别准确率增长趋势变缓,对不同测试样本的识别率均在98%以上。该算法比传统算法具有更高的识别率,尤其在对多核素混合的复杂核素谱识别方面表现出较强的优势。     

海水中134Cs、137Cs和60Co的联合分析

建立了小体积海水中¹³⁴Cs、¹³⁷Cs和⁶⁰Co的联合分析方法,确定了最佳实验条件。采用磷钼酸铵富集法对海水中放射性铯进行浓集后,其上清液利用氢氧化钴沉淀载带海水中的⁶⁰Co,用γ能谱仪进行测量。结果表明：该法对海水中放射性¹³⁴Cs、¹³⁷Cs和⁶⁰Co的回收率分别为87%~95%、87%~95%和89%~93%,检测限分别为0.048、0.051、0.046 Bq/L。另外,对2017年IAEA国际比对（IAEA-RML-2017-01）海水样品中的¹³⁴Cs、¹³⁷Cs和⁶⁰Co进行分析测量,核素分析结果的最终评价均为“通过”,验证了本实验室采用的¹³⁴Cs、¹³⁷Cs和⁶⁰Co联合分析方法的可行性和可靠性,为今后该方法在常规海洋环境放射性监测中的应用推广奠定了基础。     

某核设施周边饮用水人工放射性水平及人体健康风险评价

为掌握某核设施周边饮用水人工放射性水平并进行人体健康风险评价,收集2016—2022年该核设施周边84件自来水水中³H和10种人工特征核素(^110mAg、¹⁴⁴Ce、⁵⁸Co、⁶⁰Co、¹³⁴Cs、¹³⁷Cs、⁵⁴Mn、¹²⁴Sb、⁶⁵Zn、⁹⁵Zr)的监测数据,采用美国环境保护局(USEPA)推荐的风险评价模型评价通过饮水途径引起的健康风险。结果表明,2016—2022年该核设施周边3个监测点饮用水中³H的活度浓度分别为(0.38～3.46)、(0.38～2.34)、(0.38～1.74) Bq/L,平均值分别为0.94、0.60、0.54 Bq/L,少数调查结果高于探测限(LLD)。10种人工特征核素的活度浓度均小于LLD,远低于世界卫生组织(WHO)《饮用水水质准则》(第四版)推荐的指导值。所有检测放射性核素通过饮水途径...     

放射性核素从废物体中向外释放行为初步研究

以去离子水为初始释放环境,考察了1年释放周期内,两类典型低、中水平放射性废物固化体在被水完全浸泡情景下,3种关键核素⁶⁰Co、¹³⁷Cs、⁹⁰Sr的向外释放行为。使用平均有效扩散系数作为表征参数。多个样品的测试结果表明：3种核素向外释放表现出规律性的趋势,即¹³⁷Cs最快,⁶⁰Co最慢, ⁹⁰Sr相比居中。对于不同的核素,起始活度对释放行为的影响是不同的。借助SEM探讨了废物体微观结构对核素释放的影响。     

压水堆核电厂乏燃料水池γ剂量率变化分析

⁵⁸Co是压水堆核电厂活化腐蚀产物的核心γ源项核素,受pH值和温度变化影响,含⁵⁸Co的活化腐蚀产物溶解度将持续发生变化。福清核电厂在执行某次机组调停小修过程中,一回路冷却剂中的⁵⁸Co活度浓度,随冷却剂温度下降而持续上升;在完成某次换料大修卸料工作后,乏燃料水池水温上升,池内⁵⁸Co活度浓度也随之升高,导致乏池表面最高γ剂量率达到了设计值的10倍左右。通过分析两个案例中,⁵⁸Co活度浓度、γ剂量率水平和温度变化趋势,对比工艺系统的运行记录,可以确认:两次⁵⁸Co活度浓度的升高,均与溶液温度密切相关。分析结果表明,在酸性环境下,含⁵⁸Co的活化腐蚀产物,其溶解度在一定温度范围内具有正温度系数,溶解度将随温度上升而增大;达到最大值后,溶解度表现出负温度系数,溶解度随温度上升而减小。根据该结论,通过启动乏燃料水池备用冷却回路,降低乏池温度,成功减小了池内的⁵⁸Co活度浓度,乏池表面γ剂量率迅速恢复至正常水平,避免了后续燃料操作人员的额外剂量照射。该实践的成功,对抑制和去除压水堆核电厂活化腐蚀产物中的⁵⁸Co,提供了新的思路。     

HPGe γ谱仪测量级联γ辐射152Eu、133Ba、60Co核素活度的方法

给出了HPGe γ谱仪测量级联γ辐射核素活度的一种实用方法,在探测器与样品之间放置一定厚度的水吸收层,能够很好降低探测效率,显著降低级联γ符合效应和偶然符合效应的影响。实验表明,TC-45样品中¹⁵²Eu、¹³³Ba、⁶⁰Co核素活度的探测效率和测量活度相对偏差随水吸收层厚度增加遵循指数衰减规律,当厚度增加到70 mm以上,其测量活度相对偏差小于4%。     

核电厂关键核素在海洋沉积物上的吸附动力学

为研究核电厂关键核素在海洋沉积物上的吸附动力学过程,通过静态批式实验获得三种沉积物对核素⁹⁰Sr、¹³⁷Cs、⁵⁴Mn、⁶⁰Co的吸附动力学曲线,采用多级吸附动力学模型对实验数据进行拟合,得出以下结论：⁹⁰Sr、¹³⁷Cs、⁵⁴Mn、⁶⁰Co在三种沉积物上的分配系数（Kd）分别为1.8~3.0、71.5~128.0、23.1~167.0、160.0~188.0 mL/g;采用一级吸附动力学模型所得Kd与实验所得Kd较为符合,说明4种核素在三种沉积物上的吸附行为可由一级吸附点位进行表征;获得了各样品的吸附动力学关键参数,包括吸附速率常数、解吸速率常数及单位最大吸附量。     

Plasma-assisted Co/Zr-metal organic framework catalysis of CO_2 hydrogenation:influence of Co precursors

In this study, Co/Zr-metal organic framework(MOF) precursors were obtained by a roomtemperature liquid-phase precipitation method and the equivalent-volume impregnation method,respectively, using a Zr-MOF as the support, and Co/Zr-MOF-M and Co/Zr-MOF-N catalysts were prepared after calcination in a hydrogen–argon mixture gases(V_(Ar):V_(H_2)= 9: 1) at 350 °C for 2 h. The catalytic activities of the prepared samples for CO_2 methanation under atmosphericpressure cold plasma were studied. The results showed that Co/Zr-MOF-M had a good synergistic effect with cold plasma. At a discharge power of 13.0 W, V_(H_2):V_(CO_2)= 4: 1 and a gas flow rate of 30 ml·min~(-1), the CO_2 conversion was 58.9% and the CH_4 selectivity reached 94.7%,which was higher than for Co/Zr-MOF-N under plasma(CO_2 conversion 24.8%, CH_4 selectivity 9.8%). X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N_2 adsorption and desorption(Brunauer–Emmett–Teller) and x-ray photoelectron spectroscopy analysis results showed that Co/Zr-MOF-M and Co/Zr-MOF-N retained a good Zr-MOF framework structure, and the Co oxide was uniformly dispersed on the surface of the Zr-MOF. Compared with Co/Zr-MOF-N, the Co/Zr-MOF-M catalyst has a larger specific surface area and higher Co~(2+)/Cototaland Co/Zr ratios. Additionally, the Co oxide in Co/ZrMOF-M is distributed on the surface of the Zr-MOF in the form of porous particles, which may be the main reason why the catalytic activity of Co/Zr-MOF-M is higher than that of Co/ZrMOF-N.     

NO_x storage and reduction assisted by non-thermal plasma over Co/Pt/Ba/γ-Al_2O_3 catalyst using CH_4 as reductant

N_Ox storage and reduction(NSR) technology has been regarded as one of the most promising strategies for the removal of nitric oxides(NO_x) from lean-burn engines, and the potential of the plasma catalysis method for NO_x reduction has been confirmed in the past few decades. This work reports the NSR of nitric oxide(NO) by combining non-thermal plasma(NTP) and Co/Pt/Ba/γ-Al_2O_3(Co/PBA) catalyst using methane as a reductant. The experimental results reveal that the NO_x conversion of NSR assisted by NTP is notably enhanced compared to the catalytic efficiency obtained from NSR in the range of 150 °C–350 °C, and NO_x conversion of the 8% Co/PBA catalyst reaches 96.8% at 350°C. Oxygen(O_2) has a significant effect on the removal of NO_x, and the NO_x conversion increases firstly and then decreases when the O_2 concentration ranges from 2% to 10%. Water vapor reduces the NO_x storage capacity of Co/PBA catalysts on account of the competition for adsorption sites on the surface of Co/PBA catalysts. There is a negative correlation between sulfur dioxide(SO_2) and NO_x conversion in the NTP system, and the 8% Co/PBA catalyst exhibits higher NO_x conversion compared to other catalysts, which shows that Co has a certain SO_2 resistance.     

Accurate quantitative CF-LIBS analysis of both major and minor elements in alloys via iterative correction of plasma temperature and spectral intensity

The chemical composition of alloys directly determines their mechanical behaviors and application fields.Accurate and rapid analysis of both major and minor elements in alloys plays a key role in metallurgy quality control and material classification processes.A quantitative calibration-free laser-induced breakdown spectroscopy (CF-LIBS) analysis method,which carries out combined correction of plasma temperature and spectral intensity by using a secondorder iterative algorithm and two boundary standard samples,is proposed to realize accurate composition measurements.Experimental results show that,compared to conventional CF-LIBS analysis,the relative errors for major elements Cu and Zn and minor element Pb in the copperlead alloys has been reduced from 12％,26％ and 32％ to 1.8％,2.7％ and 13.4％,respectively.The measurement accuracy for all elements has been improved substantially.     

参加WHO IRC矿泉水中低水平放射性的分析比对

本文报道了1988—1989年我院参加世界卫生组织国际放射性参考中心(WHO IRC)组织的矿泉水中放射性分析比对的结果。参加这次分析比对的有14个国家的25个实验室,要求分析的核素包括天然铀、~(234)U、~(235)U、~(238)U、~(226)Ra 和~(210)Po,其放射性浓度在0.001—0.2 Bq/L 之间。有22个实验室向IRC 报告了分析结果,完成全部测定的实验室有5个(包括 IRC 和我院)。分析比对结果表明,我院的各项分析值与 IRC 参考值或各实验室的平均值比较接近。     

全国水体中天然放射性核素浓度调查的质量保证

本文总结了全国水体中天然放射性核素浓度调查的质量保证工作，内容包括调查中的质量管理、各种核素浓度量值的可追溯性以及实验室分析的质量控制。由本实验室制备的各种参考溶液经中国计量科学研究院等实验室核实，其量值可追溯到国家计量部门。有３１个实验室参加了分析方法的考核，结果表明，Ｕ、Ｔｈ、２２６Ｒａ和Ｋ的分析误差在±１５％以内的实验室分别占９６．８％、９６．８％、８７．１％和８７．１％。全部实验室测定上述核素的误差均小于±３５％。     

核素迁移现场试验的辐射环境影响评价

本文简述了核素迁移现场试验中对辐射环境安全的基本考虑、环境质量监测结果和试验结束后污染土壤的回收结果。监测结果表明 ,试验场周围辐射环境质量未因试验活动引起可察觉的变化 ,试验未对环境造成污染。示踪核素 60 Co、13 4Cs的回收率均超过 99.99%。回收后 ,天然条件下的试验坑内残留的 3 H将保持在浅层土壤内 ,经蒸发逐渐进入大气 ;喷淋条件下的试验坑内残留的 3 H将保持在深层土壤内 ,在全部衰变前不会进入含水层。 85Sr在回收前已几乎全部衰变。回收的污染土壤运回本院用于放射生态学实验研究。试验现场土壤中残留的核素 ,无论总量还是浓度 ,都远低于《国际电离辐射防护和辐射源安全的基本安全标准》中给出的相应的豁免值     

~(60)Co-γ射线辐照合成P(AA-co-AM)/FA高吸水性复合材料

利用~(60)Co-γ射线引发合成聚丙烯酸/丙烯酰胺/黄腐酸(P(AA-co-AM)/FA)高吸水性复合材料。探讨了在室温下,吸收剂量、黄腐酸的添加量对高吸水性复合材料吸水倍率的影响,研究在60℃环境下的保水率,同时利用红外分析(FTIR)、扫描电镜(SEM)对复合材料进行结构分析。结果表明:高吸水复合材料在去离子水和w=0.9%NaCl溶液中最好吸水倍率分别为437倍、61倍,当黄腐酸添加质量分数为15%时,在60℃环境下放置12h,其保水率为54%。该方法提高了材料的吸水保水性能,克服了传统合成方法污染大、能耗高等问题,合成的高吸水性材料适合制作农林保水剂。     

Investigating the influence of gamma ray energies and steel fiber on attenuation properties of reactive powder concrete

The effect of gamma ray energies and volume ratio of micro steel fiber (1 and 1.5％) on attenuation properties of reactive powder concrete (70 MPa compressive strength) was investigated.Different characteristics have been considered such as linear attenuation coefficient,mass attenuation coefficient,and half-value thickness.Sodium iodide crystal with a gamma ray spectrometer and collimated beam of gamma ray has been implemented to perform the experimental test.Three sources (Cs-137,Co60,and Bi-207) with energies of (0.662,1.17 1.33,0.569,and 1.063)MeV were adopted in the test.The results obtained indicated that mass attenuation coefficient is proportioned inversely with gamma ray energies and directly with a volume ratio of micro steel fiber.The linear attenuation coefficient and half-value thickness of the tested samples have been calculated and discussed.The obtained results showed that increasing the volume ratio of steel fiber has modified the adequacy of the reactive powder concrete as a shielding element since it increases the density and reduces the half-value thickness.     

Quantitative analysis of the content of nitrogen and sulfur in coal based on laserinduced breakdown spectroscopy: effects of variable selection

Coal is a crucial fossil energy in today's society,and the detection of sulfir(S) and nitrogen(N)in coal is essential for the evaluation of coal quality.Therefore,an efficient method is needed to quantitatively analyze N and S content in coal,to achieve the purpose of clean utilization of coal.This study applied laser-induced breakdown spectroscopy(LIBS) to test coal quality,and combined two variable selection algorithms,competitive adaptive reweighted sampling(CARS) and the successive projections algorithm(SPA),to establish the corresponding partial least square(PLS) model.The results of the experiment were as follows.The PLS modeled with the full spectrum of 27,620 variables has poor accuracy,the coefficient of determination of the test set(R~2 P) and root mean square error of the test set(RMSEP) of nitrogen were 0.5172 and 0.2263,respectively,and those of sulfur were0.5784 and 0.5811,respectively.The CARS-PLS screened 37 and 25 variables respectively in the detection of N and S elements,but the prediction ability of the model did not improve significantly.SPA-PLS finally screened 14 and 11 variables respectively through successive projections,and obtained the best prediction effect among the three methods.The R~2 P and RMSEP of nitrogen were0.9873 and 0.0208,respectively,and those of sulfur were 0.9451 and 0.2082,respectively.In general,the predictive results of the two elements increased by about 90% for RMSEP and 60% for R2 P compared with PLS.The results show that LIBS combined with SPA-PLS has good potential for detecting N and S content in coal,and is a very promising technology for industrial application.     

Atmospheric-pressure dielectric barrier discharge generation by a full-bridge flying capacitor multilevel inverter

A new configuration of a resonant full-bridge flying capacitor multicell inverter has been designed and constructed with the aim of achieving an extended output voltage frequency range with low harmonic distortion and reduced semiconductor commutation losses. This configuration was tested as a power supply for two different coaxial dielectric barrier discharge reactors, one of them employed for electric characterization and the other one for inorganic compound elimination in an aqueous solution. Two different gas mixtures, 90% Ar–10% O_2 and80% Ar–20% O_2, were individually supplied during the experiments; the results showed a highefficiency removal of meta-cresol(m-cresol) to the order of 98%, which was obtained by adding more oxygen to the plasma gas mixture.