Investigation of metal matrix systems for cosmogenic Al analysis by accelerator mass spectrometry

We report experiments designed to help optimize accelerator mass spectrometry (AMS) of ²⁶Al (in the form of Al₂O₃) for geochronologic and geomorphologic applications. Analysis times are long and the precision of AMS are restricted by counting statistics for ²⁶Al, which are in turn limited by the intensity of Al⁻ beam currents. We show that ion beam currents are affected by the metal matrix in which Al₂O₃ is dispersed, by the matrix-to-Al₂O₃ mixing ratio, and for at least some matrices, such as Ag, by the depth to which the sample is packed in the AMS cathode. Typical instantaneous Al⁺⁷ currents (μA) produced by the LLNL CAMS Cs sputter ion source and measured in a Faraday cup after the accelerator are 2.26 for samples in Ag, 2.17 in Re, 2.00 in Nb, 1.92 in V and 1.73 in Mo. The AMS counting efficiency (Al⁻ ions detected per Al atom loaded in the target) for a constant analysis time (900 s) and for equimolar mixtures of Al₂O₃ and matrix is in the range of 6 × 10⁻⁵–9 × 10⁻⁵ in the order Ag > Re > Nb > V > Mo. Additionally, we observed a correlation between the ion detection efficiency (Al ions detected per Al atoms loaded) and the matrix work function and inverse vaporization enthalpy of the matrix and beam current. Typical currents (μA) obtained with elemental Al are 13.3 for samples in no matrix, 3.23 in V, 3.14 in Nb, 3.07 in Re, 2.85 in Mo, 1.46 in Ag. The ion detection efficiency for elemental Al correlates strongly with matrix electron affinity. Thus, our data indicate that the current practice of mixing Al₂O₃ with Ag is reasonable until a means is found to produce cathodes of elemental Al.     

High precision C AMS at CIRCE

The CIRCE AMS system started operation in March 2005. The measurement of isotopic ratios ¹⁴C/¹²C in samples of archaeological and environmental interest has rapidly attained high precision and accuracy levels in routine operation. The results of the intercomparison campaign in the framework of the VIRI program, as well as the outcome of a statistical analysis of the about 200 control measurements performed with standard samples, have shown the capability of the whole system for high precision measurements (δR/R < 0.3%), allowing systematic investigations in both archaeological and environmental sciences. ²⁶Al AMS has been implemented for the measurement of the astrophysically relevant ²⁵Mg(p,γ)²⁶Al reaction cross section, while a beam line is under construction for the measurement of actinides isotopic ratios.     

环境中129 I的AMS方法测定

基于中国原子能科学研究院的串列静电加速器在我国建立了超高灵敏加速器质谱技术测定＾１２９Ｉ核素的方法，对我国可能受到人工放射性影响的环境中的＾１２９Ｉ进行了初步研究。     

10Be and 26Al measurements at the Zurich 6 MV Tandem AMS facility

The setups for the ¹⁰Be and ²⁶Al AMS measurements at the Zurich 6 MV EN Tandem AMS facility are presented and data analysis procedures for both radionuclides are discussed. Performance parameters of the system are shown. In-house AMS standards are compared to commercially available AMS standards.     

中子辐照对耐事故燃料FeCrAl合金力学性能的影响研究

FeCrAl合金具有良好的抗高温氧化和力学性能,能够作为燃料包壳材料。为研究FeCrAl合金的辐照力学性能,开展了不同元素成分含量和2×1019 cm?2、8×1019 cm?2 2种中子注量辐照下的FeCrAl合金力学性能试验,并在室温和380℃下测试了FeCrAl合金的拉伸性能,获得了不同Cr和Al含量FeCrAl合金的抗拉强度和屈服强度,并研究了Al含量、Cr/Al含量配比及中子辐照对FeCrAl合金力学性能的影响。研究表明,FeCrAl合金强度随着Al含量增加大致呈增加趋势;经2×1019 cm?2中子辐照后,FeCrAl合金强度有较大提升;再经8×1019 cm?2中子辐照后,FeCrAl合金强度升高不明显。该研究结果为耐事故燃料（ATF）包壳材料的研发选型提供了重要的数据支撑。      

Status and research programs of the multinuclide accelerator mass spectrometry system at the University of Tsukuba

We present the current status and research programs of a multinuclide accelerator mass spectrometry (AMS) system on the 12UD Pelletron tandem accelerator at the University of Tsukuba (Tsukuba AMS system), Japan. A maximum terminal voltage of 12 MV is available for the AMS system. The Tsukuba AMS system can measure environmental levels of long-lived radioisotopes of ¹⁴C, ²⁶Al, ³⁶Cl and ¹²⁹I by employing a molecular pilot beam. Recently, enhancements in AMS techniques and equipment, including sample preparation, the ion source and the data acquisition system, have improved the performance of ³⁶Cl-AMS. The standard deviation of fluctuations is typically ±2%, and the machine background level for the ³⁶Cl/Cl ratio is lower than 1 × 10^?15 with a halite sample. We have measured over 500 samples in 1 year, including samples for earth and environmental sciences and nuclear safety research.     

超灵敏小型回旋加速器质谱计分析多种放射性核素的可行性

理论分析和实验结果表明，超灵敏小型回旋加速器质谱计分析的放射性核素主要有＾１４Ｃ、＾３Ｈ、＾２６Ａｌ＾４０Ｋ、＾４４Ｔｉ等。在采取一定的技术措施后，可以分析的放射笥核素还可更多。     

Cs在碱硬锰矿固溶体中化学固溶量的研究

以cs2CO3、BaCO3、Al2O3和TiO2为原料,通过高温固相反应,合成了单相的固溶Cs的碱硬锰矿固溶体。借助于X射线衍射(XRD)、扫描电子显微镜(SEM)和波谱分析(WDS),研究了物相组成、Cs的化学固溶量等。结果表明:获得了单相的固溶Cs的碱硬锰矿固溶体,其Cs的最高化学固溶量约为0.26 mol,过量的Cs会生成Cs2Al2Ti2O8。     

AMS measurement technique after 30 years: Possibilities and limitations of low energy systems

A brief summary of the development of AMS over the last 30 years is given and major development steps for the measurement technique are described. With the appearance of compact low energy AMS systems 10 years ago, a new category of AMS instruments has been introduced. This has resulted in a boom of new AMS facilities with more than 20 installations over the last 5 years. But low energy AMS is not limited to radiocarbon only and there is a great potential for ¹⁰Be, ²⁶Al, ¹²⁹I and actinides measurements at compact AMS systems. The latest developments towards the low energy limit of AMS resulted in two new types of systems, the NEC Single Stage AMS and ETH MICADAS operating with terminal voltages of about 200 kV only. These systems have enormous impact, not only on the use of AMS in biomedical research but also on radiocarbon dating. Precision limits of radiocarbon dating will be discussed for the MICADAS type instruments.     

New results on Xi’an-AMS and sample preparation systems at Xi’an-AMS center

The Institute of Earth Environment of the Chinese Academy of Sciences and Xi’an Jiaotong University have jointly created an AMS center based on a 3 MV multi-element accelerator mass spectrometer (AMS). The main focus of the Xi’an-AMS center will be earth environmental studies, archeology and biomedical research. This paper summarizes that the end-user recognized features of the Xi’an-AMS and reports new results obtained during the final acceptance tests for nuclides ¹⁰Be and ²⁶Al, for which the background for ratio ¹⁰Be/⁹Be of 3.65 × 10⁻¹⁵ was demonstrated and the ²⁶Al precision test with terminal 3 MV was performed. We also introduce the new built graphite and BeO sample preparation systems and the preparation procedures. We also discuss the recent measurements obtained using our new machine after the acceptance tests.     

超大剂量6MeV电子束照射对大鼠脑Ca2+、Mg2+含量的影响

观察超大剂量6 MeV电子束照射对大鼠脑Ca2+、Mg2+含量的动态变化,探讨其在放射性脑损伤发病机制中的作用.对SD大鼠用6MeV电子线进行10Gy、20Gy和30Gy全脑单次照射,应用等离子直读光谱仪定量分析大鼠脑放射性损伤后不同时间、不同剂量脑组织中Ca2+、Mg2+含量的动态变化,用干-湿重法测定脑组织含水量.大鼠全脑受照射后,均存在脑组织中Ca2+含量升高、Mg2+含量下降和脑水肿的发生.其中20 Gy照射后24 h脑组织中Ca2+含量与对照组相比有显著升高(p＜0.05),Mg2+含量在照后7天与对照组相比有显著下降(p＜0.05).在照后7天,上述各指标变化的幅度为30Gy组＞20Gy组＞10Gy组.基于大鼠放射性脑损伤后脑组织中Ca2+、Mg2+含量发生的变化,探讨了电离辐射所致脑损伤的机理.     

The Spectral Emission Characteristics of Laser Induced Plasma on Tea Samples

Laser induced breakdown spectroscopy(LIBS) provides a useful technique for food security as well as determining nutrition contents.In this paper,optical emission studies of laser induced plasma on commercial tea samples were carried out.The spectral intensities of Mg,Mn,Ca,Al,C and CN vibration bands varying with laser energy and the detection delay time of an intensified charge coupled device were studied.In addition,the relative concentrations of six microelements,i.e.,Mg,Mn,Ca,Al,Na and K,were analyzed semi-quantitatively as well as H,for four kinds of tea samples.Moreover,the plasma parameters were explored,including electron temperature and electron number density.The electron temperature and electron number density were around 11000 K and 10~(17) cm~(-3),respectively.The results show that it is reasonable to consider the LIBS technique as a new method for analyzing the compositions of tea leaf samples.     

Study of Al measurement on the Shanghai Mini-cyclotron based AMS

We present a modification to the ¹⁴C-dedicated SMCAMS (Shanghai mini-cyclotron based AMS) system to allow the measurement of ²⁶Al for biomedical applications with the existing devices. This is accomplished by determining the turn number, harmonic number and RF frequency theoretically and then making the appropriate orbit programming and beam optics calculation and experimental adjustments. The tests were conducted using pencil graphite (for the carbon pilot beam), Al₂O₃ powder and metal aluminum to accelerate ions with mass number of 24, 25, 26 and 27. The frequency response curves for those ions are shown. Finally, the Al₂O₃ standard sample with a known isotope ratio of 1.0 × 10⁻¹⁰ is measured. The ²⁶Al⁻ ions are detected and its frequency response curve shows the peak of ²⁶Al⁻ though very weak is well separated from the most neighboring interfering molecular ions ²⁵MgH⁻.     

基于加速器质谱测量的~(41)Ca植物示踪样品制备方法研究

基于加速器质谱测量方法研究~(41)Ca植物示踪样品的制备。~(41)Ca是宇宙成因核素,半衰期较长,且对植物的代谢具有重要的作用。加速器质谱应用长寿命核素,检测方法具有灵敏度高、放射性剂量小、精度高、测量区间大、示踪周期长等优点。离子源引出束流是衡量加速器质谱灵敏度的重要参数,而较高束流强度的引出束流可以提高加速器质谱的灵敏度。为了获得较高的束流强度,本工作系统研究了~(41)Ca植物示踪样品的湿法、干法、以及湿法和干法相结合的二次氟化法,以建立~(41)Ca植物示踪样品制备流程,确定最高束流强度引出时的最优化~(41)Ca植物示踪样品制备参数,为~(41)Ca植物示踪样品广泛应用提供实验基础。     

用于高灵敏度AMS10Be测量的气体探测器

¹⁰Be是加速器质谱（AMS）测量中重要性仅次于¹⁴C的核素,在第四纪地质研究等方面发挥着重要作用。为更好地开展岩石暴露年龄测定和黄土中¹⁰Be浓度测量等应用研究,北京大学加速器质谱（PKUAMS）在深入研究离子鉴别物理过程的基础上,设计研制了1台气体探测器,¹⁰Be高能端测量效率达90%以上,¹⁰Be粒子计数率明显增加。在离子源引出只有1.2μA（最大值可达2μA）的情况下,标准样品NIST的¹⁰Be粒子计数率已达23s^-1。     

10Be/9Be标准样品的制备和加速器质谱测量

采用同位素稀释法由¹⁰Be标准参考物质SRM4325制备系列 ¹⁰Be/⁹Be标准样品,在北京HI-13串列加速器的AMS系统上对该系列标准（n(¹⁰Be)/n(⁹Be)范围为2.68×10^-11~2.38×10^-12）进行测量。测量结果显示，n(¹⁰Be)/n(⁹Be)测量值与标称值呈良好线性关系，且归一化后的测量值与标称值吻合。该系列标准可用于北京HI-13串列加速器的AMS系统对地质环境样品中¹⁰Be/⁹Be绝对比值的准确测定。     

基于加速器质谱测量的~(14)C呼气试验样品制备方法研究

采用加速器质谱法研究~(14)C呼气试验样品的制备方法。采用长寿命放射性核素~(14)C作为示踪核素,目前已广泛应用于生物代谢、疾病诊断和脏器功能评估。离子源引出的束流强度是衡量加速器质谱灵敏度的重要参数,为了获得较高的束流强度,本工作系统研究了~(14)C呼气试验样品的石墨法、碳酸盐法两种制备方法,拟建立~(14)C呼气试验样品制备流程,确定最高束流强度引出时的最优~(14)C呼气试验样品制备参数,为~(14)C呼气试验广泛应用提供实验基础。     

加速器质谱测量用HfF_4的固相合成研究

HfO2样品通过分离纯化流程后,与NH4HF2进行固相反应制成HfF4,并用加速器质谱进行测量。结果表明:α-安息香肟萃取是降低182W含量的重要步骤;固相合成法制备的HfF4样品中180HfF5-的引出束流强度是同等条件下液相合成法的3-4倍;制样方法(固相合成法、液相合成法)对182W/Hf值影响不大;HfF4中182W/Hf值低至10-11g·g-1量级。