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。     

7Be在Au中衰变率的精确测量

对在通常实验室环境下注入到Au中的⁷Be发生电子俘获的半衰期进行测量。共测量4.8个半衰期，测得T_1/2=（53.245±0.003）d。此测量结果可作为研究⁷Be衰变率随环境不同而发生变化时的参照值。     

气溶胶7Be活度浓度的测量方法及其应用

用三层滤膜法测定⁷Be气溶胶的过滤效率,并对测量结果进行衰变修正,得到过滤效率为85.7%。同时,分析研究杭州附近气溶胶⁷Be活度浓度的年变化规律,得出主要原因是季节性降雨。     

基于SnF2靶样的加速器质谱测量裂变产物126Sn的方法研究

在中国原子能科学研究院HI-13串列加速器质谱系统上建立了以SnF₂为靶样,引出SnF₃^-分子负离子形式的¹²⁶Sn-AMS分析方法。介绍了用于AMS测量的¹²⁶Sn实验室参考标准的研制以及靶物质SnF₂的化学制备过程,通过引束实验确定了可将同量异位素¹²⁶Te本底干扰压低2～3个量级的SnF₃^-分子负离子引出形式,实现了¹²⁶Sn束流的传输以及同量异位素的探测和鉴别。对制备的3个标准样品（¹²⁶Sn/Sn原子个数比为1.033×10^-8、4.54×10^-9、6.43×10^-10）的测量结果显示,¹²⁶Sn/Sn原子个数比测量值与标称值呈良好的线性关系（R²=0.999）,通过测量空白样品获得系统探测¹²⁶Sn测量的灵敏度为（1.92±1.13）×10^-10。     

Ti、Zr、Er及Nd等金属氚化物的3He释放

利用四极质谱计（QMS）法测量了Ti、Zr、Er及Nd等4种单质金属的氚化物³He释放,通过数年监测与数据积累,对这4种金属氚化物的3He释放行为进行了比较研究。结果表明,它们贮存早期的³He释放速率极低,其释放速率均不及生成速率的1%,其中,Ti、Zr氚化物³He释放系数（RF）为10^－6～10^－5量级,Er、Nd氚化物的3HeRF为10^－3量级,随着贮存时间的增加,当金属氚化物内积累较多的3He时,其RF会迅速增长至10^－1量级,释放速率接近生成速率。     

镝活化法测量低产额脉冲中子

设计一个快中子聚乙烯慢化体，用来慢化加速器的d-T和d-D中子，利用¹⁶⁴Dy(n,γ)¹⁶⁵Dy^m在热中子区极高的反应截面，得到半衰期为75s的¹⁶⁵Dy^m，使用HPGe探测器测量¹⁶⁵Dy^m放出的γ射线。由于测得的γ射线与加速器的中子产额成一定比例，故通过这种方法可测量脉冲中子源的中子产额。     

AMS 10Be测量本底研究和改进

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.为开展岩石暴露年龄测定和黄土中10Be含量测量等应用研究,北京大学加速器质谱(PKUAMS)在设备改进的基础上对10Be测量本底进行了较为系统的研究,使测量本底达到了6×10-15.本工作主要介绍AMS 10Be测量本底的主要来源,从提高10Be离子计数率与抑制7Be干扰本底两个方面对10Be测量本底进行了较为系统的研究与改进.     

胆碱模块自动化合成11C-carfentanil及Micro PET显像

为快速、高效合成中枢神经阿片受体显像剂¹¹C-carfentanil(¹¹C-CFN),对国产商业化¹¹C-胆碱合成模块略做改动,并优化了合成条件。结果表明,采用4-哌啶乙酸钠,4-[(1-丙羰基)苯胺]-1-(2-苯乙基)[钠盐]作前体,DMSO作溶剂,¹¹CH_3-triflate作甲基化试剂,在胆碱模块上采用反应瓶法,可自动化合成¹¹C-CFN。合成的¹¹C-CFN活度＞14.8 GBq、比活度＞1.4×10¹⁴Bq/g、放化纯度＞99%,校正合成效率＞80%（n=55,以¹¹CH₃-triflate计算）,全部合成时间为18 min。经Micro PET/CT证实,¹¹C-CFN可用于μ阿片受体的PET显像研究。     

125I粒子组织间植入近距离治疗恶性肿瘤

采用¹²⁵I粒子植入法对20例恶性肿瘤患者的24个病灶进行治疗,以评价¹²⁵I粒子组织间植入恶性肿瘤的可行性及不良反应。术前制定肿瘤组织间三维立体定向放射治疗计划,在全麻剖腹直视下、全麻腹腔镜下或局麻CT、局麻彩色多普勒导向下经皮穿刺将¹²⁵I粒子植入恶性肿瘤病灶内。20例患者¹²⁵I粒子植入均顺利完成,术中及术后1周观察粒子在病灶内的分布基本与计划相符合,未观察到粒子迁移;术中及术后不良反应较为轻微且易于处理;多数患者临床症状得到不同程度的缓解,血清肿瘤标志物水平呈现不同程度的下降; 病情完全缓解（CR）20.00%（4/20例）, 部分缓解（PR）35.00%（7/20例）, 稳定（SD）30.00%（6/20例）,进展（PD）15.00%（3/20例）,总有效率（CR+PR）55.00%（11/20例）。以上结果表明,¹²⁵I粒子组织间植入近距离内放射治疗恶性肿瘤施术方便、安全有效,具有较高的临床价值,值得进一步推广及深入研究。     

D-半乳糖-1-13C的合成与表征

以硝基甲烷¹³C为原料合成D-半乳糖-1-¹³C。采用分离中间体硝基糖醇的方式,简便拆分差向异构体D-半乳糖和D-塔罗糖,合成产物的总产率为42.6%,¹³C丰度为99.1%,光学纯度为100%,化学纯度为99.7%。以高效液相色谱 蒸发散射光检测器（HPLC-ELSD）、液相色谱-质谱联用仪（LC-MS）和核磁共振（¹H NMR）对所得产物进行结构表征,确定产物结构为D-半乳糖-1-¹³C。     

Be AMS measurements at low energies (E < 1 MeV)

The longlived isotope ¹⁰Be is of great importance in earth sciences for dating applications, reconstruction of the solar activity or in climate research. Routine AMS measurements with BeO samples are performed on accelerators with a terminal voltage above 2 MV. Applying the degrader foil technique for boron suppression, first tests with BeO samples on the 0.6 MV ETH/PSI machine were limited by background to a ¹⁰Be/⁹Be ratio of 10⁻¹³. The background was identified as ⁹Be which reaches the detector by scattering processes. By applying an additional magnetic mass filter to the high energy mass spectrometer the background was effectively removed. A ¹⁰Be/⁹Be background ratio of <5 × 10⁻¹⁵ was achieved. The overall efficiency (detected ¹⁰Be compared to BeO⁻ injected into the accelerator) was 7-8%.     

Carrier-free measurements of natural 10Be/9Be ratios at low energies

At ETH Zurich a new method to measure directly the natural ¹⁰Be/⁹Be ratio of a sample with the compact (0.6 MV) AMS system Tandy has been developed, which allows us to use standard sample preparation methods and AMS techniques. Our results show that carrier-free measurements with compact AMS machines represent a fast, less expensive and more precise alternative for applications where only the relative variation of the ¹⁰Be/⁹Be ratio is needed. Increased source efficiency for (artificial) low carrier samples has been found. If this effect could be exploited for natural samples, it would open the field for other applications like in situ ¹⁰Be-dating of quartz with compact, low energy AMS systems.     

Competitive 10Be measurements below 1 MeV with the upgraded ETH–TANDY AMS facility

Competitive ¹⁰Be measurements at energies as low as 0.75 MeV are now possible with the compact ETH AMS system TANDY. In this paper we describe and discuss the modifications that led to the significantly improved performance for ¹⁰Be at the 0.6 MV accelerator. Results from the first routine measurement show that ¹⁰Be on the upgraded TANDY is now fully competitive with larger AMS systems with respect to background and measurement precision. The total efficiency for ¹⁰Be is comparable to our large 6 MV Tandem system and thus sufficient for the full range of applications in the Earth and Environmental Sciences.     

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.     

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.     

Applications of a compact ionization chamber in AMS at energies below 1 MeV/amu

The increasing demand for measuring long-lived radionuclides with small AMS machines at energies below 1 MeV per nucleon raises the need for compact detectors which still have a decent energy resolution and allow for a clear identification of the incident particles. Based on a design by the AMS group at the ETH Zurich a compact gas ionization chamber was built and installed at the 3 MV tandem AMS facility VERA (Vienna Environmental Research Accelerator). The main challenge in AMS is the detection of rare isotope species in the presence of strong isotopic and isobaric interferences. The task of the ionization chamber is the suppression of the unwanted isobar by separating the ions via their different stopping powers. Measurements of ³⁶Cl at VERA showed an achieved suppression of the unwanted stable isobar ³⁶S of 3 × 10⁻⁴ and measurements of ¹⁰Be showed an achieved suppression of ¹⁰B of at least 3 × 10⁻⁶. Additional suppression of the isobaric ions can be achieved by a degrader foil technique applied to ¹⁰Be measurements by G.M. Raisbeck. In combination with the new ionization chamber the achieved suppression of ¹⁰B is at least 10⁻¹⁰. Measurements of blank samples at VERA show that the background for AMS with ¹⁰Be is below 2 × 10⁻¹⁵.     

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.     

Towards more precise Be and Cl data from measurements at the 10 level: Influence of sample preparation

The spreading application of accelerator mass spectrometry (AMS) to the geosciences will require measurement of increasing numbers of samples with low ¹⁰Be/⁹Be and ³⁶Cl/Cl isotopic ratios. To distinguish radionuclide concentrations in samples from corresponding processing blanks, samples must be prepared using stable isotope carriers with low intrinsic radionuclide concentrations. Measurements at different AMS facilities have shown that commercially available ⁹Be carriers rarely meet these requirements and use of ⁹Be carriers prepared from Be-containing minerals such as Be₂SiO₄ is advisable. For precise determinations at the low 10⁻¹⁴ level, samples need to produce the highest ⁹Be currents possible. Measurements performed at the two AMS facilities in France show that mixing BeO with Nb powder generally yields higher ⁹Be currents than mixing with Ag powder. Contamination of BeO by other elements such as Ti or Al will reduce the current by a simple dilution effect, thus limiting the statistical precision with which ¹⁰Be can be determined. In the case of ³⁶Cl analyses, repeated water-leaching of calcite samples sufficiently removes all atmospheric ³⁶Cl contamination, allowing determination of terrestrial cosmogenic in situ produced ³⁶Cl concentrations for surface exposure dating.     

On the measurement of 10Be on the 1 MV compact AMS system at the Centro Nacional de Aceleradores (Spain)

In this work we present the most recent improvements performed by our group on ¹⁰Be measurements on the 1 MV AMS system recently set up at the CNA (Centro Nacional de Aceleradores), in Seville (Spain). Our efforts have been focused on the study of the viability of our system for BeO and BeF^? measurements. To achieve this, different standard materials have been measured to demonstrate the reliability of the system for BeO measurements in a wide ¹⁰Be/⁹Be atomic ratio range and several environmental samples have been studied both at the 1 MV AMS CNA facility and at the 6 MV AMS ETH-PSI facility of Zurich to validate our measurements. The results show a good agreement between laboratories. New experiments also have been carried out selecting 1+ and 2+ charge states at the exit of the accelerator and inserting Si₃N_3.1 foils with different thicknesses to separate ¹⁰Be from its isobar, ¹⁰B. The influence of each foil on the overall transmission (detected ¹⁰Be compared to BeO^? injected into the accelerator) and background level was also assessed. In addition some tests were also done to assess the viability of BeF₂ and BaBeF₄ measurements at our system. Several metal matrices and cathode preparation procedures for BeO samples were investigated to maximize current and cathode lifetime.