分类: 核科学技术 >> 核科学与技术 提交时间: 2025-03-28
摘要: Efficiency calibration is a critical step that enables the conversion of the detectors’ count rate into the activityof radionuclides in the examined parts for in vivo measurement. However, to date, there hasn’t been awell-accepted framework for efficiency calibration. As such, it is often found researchers employ various kindsof anthropomorphic phantoms with considerably different patterns of radionuclide distribution coupling withdrastically different numbers of detectors to derive the calibration factor, rendering the cross-comparison amongstudies challenging. Moreover, some studies employ virtual calibration, whereas others prefer experimental calibration,though their equivalency has not been fully explored. In this paper, focusing on in vivo measurement ofPb-210 in the skull, a promising technique for individualized reconstruction of radon exposure is presented, anda detailed framework for efficiency calibration covering key issues mentioned above is provided. To be specific,physical phantoms of Pb-210 in the skull are developed based on the anatomical characteristics of a Chineseadult reference male, along with the corresponding computational phantoms constructed from computed tomographyscan. In comparison, the average deviations between simulation and experimental results are within 4%for efficiency calibration at the top, left, and right sides of the head across varying detection distances. Furthermore,based on the investigation of Pb-210 distribution regions reported in literature, the calculation methodfor Pb-210 activity is improved to account for different source distributions and joint measurements with multipledetectors. The results are useful for determining the appropriate conversion procedure under differentmeasurement conditions.
分类: 生物学 >> 生物学其他学科 提交时间: 2018-07-18 合作期刊: 《古脊椎动物学报》
摘要: This paper reviews recent works on the age of Chinese terrestrial Permo-Triassic strata, mainly based on the isotopic dating and the tetrapod correlation. For the application of U-Pb dating methods for the stage-level division of Permo-Triassic strata, the best method is the Thermal Ionization Mass Spectrometer (TIMS), while the Secondary Ion Mass Spectroscopy (SIMS) can be used for many cases; however, the most popular Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS), which has nearly 4% error (>8 Myr), is of little use (Li et al., 2015).
分类: 核科学技术 >> 核科学技术其他学科 提交时间: 2024-05-08
摘要: In this study, to efficiently remove Pb(II) from aqueous environments, a novel L-serine-modified polyethylene/polypropylene nonwoven fabric sorbent (NWF-serine) was fabricated through the radiation grafting of glycidyl methacrylate and subsequent L-serine modification. The effect of the absorbed dose was investigated in the range of 5–50 kGy. NWF-serine was characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy. Batch adsorption tests were conducted to investigate the influences of pH, adsorption time, temperature, initial concentration, and sorbent dosage on the Pb(II) adsorption performance of NWF-serine. The results indicated that Pb(II) adsorption onto NWF-serine was an endothermic process, following the pseudo-second-order kinetic model and Langmuir isotherm model. The saturated adsorption capacity was 198.1 mg/g. NWF-serine exhibited Pb(II) removal rates of 99.8% for aqueous solutions with initial concentrations of 100 mg/L and 82.1% for landfill leachate containing competitive metal ions such as Cd, Cu, Ni, Mn, and Zn. Furthermore, NWF-serine maintained 86% of its Pb(II) uptake after five use cycles. The coordination of the carboxyl and amino groups with Pb(II) was confirmed using X-ray photoelectron spectroscopy and extended X-ray absorption fine structure analysis.
分类: 地球科学 >> 地质学 提交时间: 2017-08-24 合作期刊: 《古脊椎动物学报》
摘要: Tetrapod assemblages provide a useful means for global correlation of the terrestrial Triassic sedimentary deposits, but currently no reliable temporal framework has been achieved for the Middle Triassic tetrapod assemblages. Here we report U-Pb zircon chemical abrasion–thermal ionization mass spectrometry dates for five volcanic ashes interbedded with vertebrate fossils from the Ermaying and Tongchuan formations of China. Our results support a late Anisian age for the Sinokannemeyeria Fauna and an early Ladinian age for Yonghesuchus Fauna. It is now possible, through biostratigraphic correlation, to provide accurate ages to other Middle Triassic successions such as the Upper Cynognathus Assemblage Zone of the Karoo of South Africa, the Eryosuchus fauna of the Donguz Suite of Russia and the Karamayi Formation of Xinjiang, China. The base of Anisian (Lower/Middle Triassic boundary) should lie below the base of the Ermaying Formation in the Ordos Basin. 四足动物组合带是全球陆相三叠系对比的有力手段,但是迄今为止中三叠世的四足动物组合尚没有可靠的时间框架。本文报道了五个采自二马营组和铜川组,与四足动物化石共同产出的火山凝灰岩样品的锆石化学剥蚀-热电离质谱法年龄。结果表明中国肯氏兽动物群时代为安尼期晚期,而永和鳄的时代为拉丁期早期。通过生物地层对比,这一结果还为其他中三叠世的四足动物组合,如南非的犬颌兽带上部、俄罗斯的引鳄动物群以及新疆的克拉玛依组提供了准确的年龄。鄂尔多斯盆地下中三叠统界线应低于二马营组底界。
分类: 材料科学 >> 材料科学(综合) 提交时间: 2016-11-15 合作期刊: 《金属学报》
摘要: 在9Cr2WVTa低活化铁素体/马氏体钢中添加合金元素Al及Si,研究了Al、Si对9Cr2WVTa钢显微组织、力学性能、冲击性能以及耐液态Pb-Bi共晶合金(LBE)腐蚀性能的影响。结果表明Al、Si缩小9Cr2WVTa合金的奥氏体相区,促进δ铁素体的生成,且Al元素的影响更加明显。位于马氏体与δ铁素体界面的M23C6碳化物处易产生应力集中进而形成孔洞,严重降低9Cr2WVTa合金的室温冲击性能,断口呈现脆性断裂特征。通过Al、Si的复合添加,获得了具有较好力学性能和冲击性能的9Cr2WVTa合金,合金在550℃静态LBE中的腐蚀性能明显提高,其原因在于合金内层氧化层中形成的Al和Si的氧化物,提高了内层氧化层的致密性,降低了合金元素及氧的扩散速率,从而显著提高合金的耐铅铋腐蚀性能。
分类: 材料科学 >> 材料科学(综合) 提交时间: 2023-03-19 合作期刊: 《金属学报》
摘要: 在Sn, Sn-3.0Ag-0.5Cu和Sn42-Bi58 钎料中添加具有纳米结构的笼形硅氧烷齐聚物(POSS)作为增强相, 研究了增强相在恒温恒湿(85 ℃, 相对湿度85%)条件下对锡基无Pb焊层晶须生长行为的影响. 结果表明, 在恒温恒湿条件下, 锡基无Pb焊层晶须生长的驱动力是Sn 的氧化物生成引起体积膨胀从而对周围焊层产生的压应力; 添加POSS可以有效缓解金属Sn的氧化进程, 抑制Sn 的氧化物生成, 从而减缓晶须生长; 在Sn, Sn3.0Ag0.5Cu和Sn58Bi 焊层中, Sn 焊层晶须生长能力最强,Sn58Bi焊层晶须生长能力最弱.
分类: 核科学技术 >> 核材料与工艺技术 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: The existing 210Pbex mass balance models for the assessment of cultivated soil erosion are based on an assumption that 210Pbex is quite evenly mixed within the plough layer. However, the amount of 210Pbex distributed in the soils below the plough depth, like a downward tail in the lower part of the 210Pbex profile, has been largely ignored. In fact, after the initial cultivation of undisturbed soils, 210Pbex will diffuse downward from plough layer to the plough pan layer due to the concentration gradient. Assuming 210Pbex inventory is constant, the depth distribution in the two layers of the cultivated soils will achieve a steady state after continuous cultivation for 10.37 years, when 210Pbex is evenly distributed in the soils of the plough layer with an exponential concentration decline with depth in the soils of the plough pan layer, and the 210Pbex concentration at any depth will be invariable with time. The work reported in this paper attempts to explain the formation of the 210Pbex tail in the soil profile below the plough depth by theoretical derivation of the 210Pbex depth distribution process in the two layers of the cultivated soils, propose a 210Pbex mass balance model considering 210Pbex diffusion based on the existing model, and discuss the influence of the 210Pbex tail to the existing model.
分类: 材料科学 >> 材料科学(综合) 提交时间: 2017-03-31 合作期刊: 《金属学报》
摘要: 为了评价反应堆候选结构材料与液态金属的相容性,本工作针对低活化马氏体钢在液态Pb-Bi共晶中的拉伸脆化现象,采用2种拉伸速率的拉伸实验,研究了中国低活化马氏体钢(CLAM)在200~500 oC范围内的Ar气和液态Pb-Bi共晶环境中的拉伸断裂行为。结果表明,在Ar气环境中拉伸时,CLAM钢均为韧性断裂;而在液态Pb-Bi共晶环境中拉伸时,在300~450 oC温度下会出现脆性断裂现象。在300~450 oC脆化温度区间内试样强度变化不大,但总延伸率显著降低,出现“韧谷”现象。然而拉伸温度在低于或高于脆化温度区间时,脆断现象消失,总延伸率回复到与对比试样相同水平。在更低的拉伸速率下, CLAM钢发生“韧谷”现象的温度区间明显扩大,表明拉伸速率对CLAM钢在液态Pb-Bi共晶中的脆化也有影响。经低温回火硬化后,CLAM钢在液态Pb-Bi共晶中出现拉伸脆化现象是由于液态Pb-Bi接触裂纹尖端后造成表面能降低,进而降低临界解理应力而发生脆性断裂。
分类: 地球科学 >> 地理学 提交时间: 2021-12-14 合作期刊: 《干旱区地理》
摘要: 中国黄土高原保存着全世界分布范围最广、厚度最大、连续性最好的风尘堆积,是第四纪 非常有价值的陆相古气候古环境地质档案。半个多世纪以来,学界对风尘沉积的气候记录和黄 土高原的成因进行了大量研究。然而,对黄土粉尘的确切来源以及物源历史是否存在时空变迁 等问题尚存在广泛争议。通过对现有锆石年龄谱数据的统计分析,着重从黄土与周缘沙漠的亲缘关系、轨道年龄尺度和构造年龄尺度的角度着手,获得以下认识:(1)在获得北方干旱区沙漠确 切年代学信息的基础上,应用碎屑锆石 U-Pb 年龄谱法有望实现厘清黄土与风成沙之间物源亲疏 关系的远景目标。(2)现有数据识别出 L1 黄土的物源可能存在空间差异。(3)支持冰期-间冰期的 黄土物源未发生重大改变的观点。(4)在构造时间尺度上,不同地区年龄谱表现出可能发生物源 转移的时段明显重叠。(5)有限的红黏土年龄谱数据显示物源的空间差异很可能在第四纪之前就已存在。鉴于目前的数据量还较少,有必要深入开展工作。应用该方法,可以在连续的长时间尺度下对黄土物源变化历史开展研究,并为将来在黄土高原开展多地区多剖面物源对比工作积累 数据集。
分类: 材料科学 >> 材料科学(综合) 提交时间: 2023-03-19 合作期刊: 《金属学报》
摘要: 采用恒流极化, SEM, XRD, EIS 和Tafel 扫描对比研究了Pb-Ag-RE合金阳极在无Cl−和含500 mg/L Cl− H2SO4溶液中的腐蚀行为和析氧行为. 结果表明, Pb-Ag-RE阳极在含Cl−电解液中生成的氧化膜层出现“火山口”状孔洞, 合金基底上分布着大量的腐蚀坑, 呈现出明显的局部腐蚀特征. 此外, Cl−的存在会减少阳极表面氧化膜层中PbO2的含量, 抑制析氧反应中间产物的生成和吸附, 进而增加析氧反应传荷阻抗. 因此, 500 mg/L 的Cl−对Pb-Ag-RE合金阳极的耐腐蚀性能和析氧活性均会造成不利影响, 工业生产中应尽量降低电解液中Cl−的浓度.
分类: 生物学 >> 生态学 提交时间: 2018-01-05 合作期刊: 《中国生态农业学报》
摘要: 随着经济和社会的发展, 土壤重金属污染对粮食安全及人类的身体健康构成了巨大的威胁, 而目前对于土壤重金属污染的治理主要以植物修复为主。为了寻找适宜修复Cu、Pb复合污染土壤的牧草, 采用盆栽试验法通过比较紫花苜蓿(Medicago sativa)、黑麦草(Lolium perenne)、狼尾草(Pennisetum alopecuroides)的适应能力和富集特征研究了这3种常见牧草植物对受Cu、Pb复合污染土壤的修复效果。结果表明: (1)紫花苜蓿地上部和根部生物量均在Pb1处理组时最大, 显著大于其他处理组; 黑麦草地上部生物量在Cu1Pb1处理组最大, 根部生物量在Pb1处理组最大; 狼尾草地上部生物量在Cu2Pb2处理组最大, 根部生物量在Cu2处理组最大。(2)受Cu单一污染的条件下, 狼尾草抗性系数最大; 受Pb单一污染的条件下, 紫花苜蓿抗性系数最大; 受Cu-Pb复合污染的条件下, 综合来看狼尾草的抗性系数较大, 高浓度Cu处理组3种牧草植物的地上部生物量、根部生物量和抗性系数均呈现: 狼尾草>黑麦草>紫花苜蓿, 且狼尾草要显著大于黑麦草和紫花苜蓿。(3)种植3种牧草植物后, 土壤中重金属Cu、Pb含量均有所降低。在一定浓度下, 土壤Cu-Pb重金属间会相互促进对方在牧草植物中的吸收。(4)3种牧草中紫花苜蓿地上部对Cu的富集系数在Cu2Pb2处理组最大, 达到1.61, 黑麦草根部对Cu的富集系数在Cu2Pb2处理组最大, 达到3.8; 3种牧草地上部和根部对Pb的富集系数只在黑麦草根部的Cu1Pb1处理组时大于1, 达到1.46。(5)黑麦草对Pb的吸收能力较强, 且主要积累在根系; 紫花苜蓿对Cu-Pb复合污染综合修复效果最好。紫花苜蓿和黑麦草分别在Cu-Pb复合污染和Pb单一污染土壤中对Pb的转运系数大于1, 分别为2.72和2.06, 反映其对土壤中的Pb具有富集潜力。综合表明, 黑麦草对重金属Pb具有较强的耐性, 在重金属Pb单一污染土壤的的植物修复及尾矿废弃地的植被重建中, 可优先作为选择的材料; 紫花苜蓿对重金属Cu、Pb均具有较强的耐性, 在重金属Cu单一或Cu-Pb复合污染土壤的的植物修复及尾矿废弃地的植被重建中, 可优先作为选择的材料。
分类: 材料科学 >> 材料科学(综合) 提交时间: 2016-11-04 合作期刊: 《金属学报》
摘要: 采用恒流极化, SEM, XRD, EIS和Tafel对比研究了Pb-Ag-RE合金阳极在无Cl?和含500 mg/L Cl? H2SO4溶液中的腐蚀行为和析氧行为.结果表明, Pb-Ag-RE阳极在含Cl?电解液中生成的氧化膜层出现“火山口”状孔洞, 合金基底上分布着大量的腐蚀坑, 呈现出明显的局部腐蚀特征. 此外, Cl?的存在会减少阳极表面氧化膜层中PbO2的含量, 抑制析氧反应中间产物的生成和吸附, 进而增加析氧反应传荷阻抗. 因此, 500 mg/L的Cl?对Pb-Ag-RE合金阳极的耐腐蚀性能和析氧活性均会造成不利影响, 工业生产中应尽量降低电解液中Cl?的浓度.
分类: 物理学 >> 核物理学 提交时间: 2016-08-26
摘要: Measurements of the per-event charged-particle yield as a function of the charged-particle transverse momentum and rapidity are performed using p+Pb collision data collected by the ATLAS experiment at the LHC at a centre-of-mass energy of sNN−−−−√=5.02 TeV. Charged particles are reconstructed over pseudorapidity |η|<2.3 and transverse momentum between 0.1 GeV and 22 GeV in a dataset corresponding to an integrated luminosity of 1 μb−1. The results are presented in the form of charged-particle nuclear modification factors, where the p+Pb charged-particle multiplicities are compared between central and peripheral p+Pb collisions as well as to charged-particle cross sections measured in pp collisions. The p+Pb collision centrality is characterized by the total transverse energy measured in −4.9<η<−3.1, which is in the direction of the outgoing lead beam. Three different estimations of the number of nucleons participating in the p+Pb collision are carried out using the Glauber model and two Glauber-Gribov colour-fluctuation extensions to the Glauber model. The values of the nuclear modification factors are found to vary significantly as a function of rapidity and transverse momentum. A broad peak is observed for all centralities and rapidities in the nuclear modification factors for charged-particle transverse momentum values around 3 GeV. The magnitude of the peak increases for more central collisions as well as rapidity ranges closer to the direction of the outgoing lead nucleus.