Tuning method for nonuniform traveling-wave accelerating structures

The tuning method of uniform traveling-wave structures based on the non-resonant perturbation field distribution measurement has been widely used in tuning both constant-impedance and constant-gradient structures. In this paper, the method of tuning nonuniform structures is proposed on the basis of the above theory. The internal reflection coefficient of each cell is obtained from analyzing the normalized voltage distribution. A numerical simulation of tuning process according to the coupled cavity chain theory has been done and the result shows each cell is in right phase advance after tuning. The method will be used in the tuning of a disk-loaded traveling-wave structure which is being developed at the Accelerator Laboratory, Tsinghua University.     

土壤中稀土元素的形态分析

稀土元素对土壤环境的影响不但与其总量有关,而且与其化学形态关系更为密切。分别采用酸法消解和形态连续提取法对土壤样品中稀土元素总量和稀土元素的形态进行提取分析,并利用电感耦合等离子体质谱法测定了土壤样中稀土元素含量和稀土元素各形态含量。结果表明,采集土壤样品中稀土元素含量为200~1418 mg/kg,轻稀土元素含量远高于重稀土元素;稀土元素各结合形态总和相对于总量的回收率为88.2%~110%,表明采用的连续萃取法适合土壤样品中稀土元素的分析。土壤样品中稀土元素主要以残渣态存在,为33%~80%;晶体铁锰氢氧化物共沉淀态为10%~31%;腐殖质和无定形氧化物吸附态为5.0%~18%;可交换态和碳酸盐结合态为4.0%~23%;无定形铁锰氧化物共沉淀态低于3%。分析了采样点位置和稀土元素性质对稀土元素含量的影响,并讨论了土壤性质对形态分布的影响。     

分散液液微萃取-气相色谱-质谱联用法测定饮料中4种对羟基苯甲酸酯类防腐剂

对羟基苯甲酸酯是在化妆品、食品和药物制品中广泛使用的一类防腐剂.但近年来的毒理学研究表明,该类物质具有一定的雌激素活性,对皮肤、生殖和内分泌系统有不同程度的副作用,发展简单、灵敏、快速测定食品中的痕量对羟基苯甲酸酯类防腐剂的分析方法越来越受到人们的关注.     

土壤对外源钍的吸附行为表征

外源钍对土壤的污染风险和程度取决于钍在土壤中的吸附行为.以包头稀土工业区土壤样品和土壤环境矿物组分为研究对象,通过静态吸附方法研究外源钍在土壤样品和环境矿物组分(高岭土、蒙脱土、碳酸钙、水合氧化铁/锰和腐殖酸)上的吸附,并对吸附行为进行了表征.结果表明,土壤样品对外源钍有很强的吸附能力,对加入的外源钍(10-4mol/L)吸附率在97%以上;土壤环境矿物组分对加入的外源钍(1g/L)吸附率在28%～46%之间.通过扫描电镜-能谱(SEM-EDS)分析可知,外源钍进入土壤后与矿物组分发生相互作用,可能形成了稳定化钙质钍碳酸盐和钍磷酸盐;傅里叶变换红外光谱(FTIR)分析表明,钍是与土壤环境矿物组分上的活性吸附位点发生相互作用而吸附并保持在土壤中,是物理吸附和化学吸附共同作用的过程;X射线衍射分析(XRD)表明,土壤在吸附钍前后,其矿物组分基本相同,而矿物晶体相态发生明显变化.由于不同土壤矿物组分对钍的吸附方式不同,导致吸附的钍以不同形态存在于土壤中.     

氯化物发生-电感耦合等离子体发射光谱法测定含锗保健品中无机锗

基于电感耦合等离子体发射光谱(ICP-OES)法研究了无机锗和有机锗在HCl介质中的氯化物发生情况.结果表明,有机锗(Ge-132)不形成氯化物,而无机锗在以浓 HCl为载流,载气压力0.14 MPa,样品溶液中HCl浓度为6 mol/L时能实现最佳的氯化物发生效率,由此建立了含锗保健品提取液中无机锗的选择性测定新方法...     

A tuning method for nonuniform traveling-wave accelerating structures

The tuning method of uniform traveling-wave structures based on non-resonant perturbation field distribution measurement has been widely used in tuning both constant-impedance and constant-gradient structures. In this paper, the method of tuning nonuniform structures is proposed on the basis of the above theory. The internal reflection coefficient of each cell is obtained from analyzing the normalized voltage distribution. A numerical simulation of tuning process according to the coupled cavity chain theory has been done and the result shows each cell is in right phase advance after tuning. The method will be used in the tuning of a disk-loaded traveling-wave structure being developed at the Accelerator Laboratory, Tsinghua University.     

Analyzing the effects of post couplers in DTL tuning by the equivalent circuit model

Stabilization of the accelerating field in Drift Tube Linac（DTL） is obtained by inserting Post Couplers（PCs）. On the basis of the equivalent circuit model for the DTL with and without asymmetrical PCs, stabilization is deduced quantitatively： we let δω/ω0 be the relative frequency error, then we discover that the sensitivity of field to perturbation is proportional to √δω/ω0 without PCs and to δω/ω0 with PCs. Then we adapt the circuit model of symmetrical PCs for the case of asymmetrical PCs. The circuit model shows how the slope of field distribution is changed by rotating the asymmetrical PCs and illustrates that the asymmetrical PCs have the same effect as the symmetrical ones in stabilization.     

悬浮进样-电感耦合等离子体质谱水溶液校正法测定高纯石墨中的超痕量硼

建立了悬浮进样-电感耦合等离子体质谱 (SN-ICP-MS) 直接测定高纯核石墨中的超痕量硼的方法.石墨粉经过研磨和过筛后,粒径<5 μm.选择聚乙烯吡咯烷酮 (PVP)作为分散剂,石墨与分散剂优化的质量比(m /m)为 0.5.通过磁力搅拌保证样品溶液的均一性与稳定性.以 0.1 mol/L 氨水维持悬浮液(pH 10)和消除硼的记忆效应.ICP-MS选择高分辨模式(0.6 amu)消除基体 12C的拖尾干扰.在等离子体中加入流量为60 mL/min的氧气,以消除有机试剂对样品锥和截取锥产生的积碳影响,还可以加速样品粒子在等离子体中的解离.采用水溶液外标法定量,以Be为内标元素考察了对基体效应校正情况.本方法的线性范围为2～200 μg/L, 相关系数为0.9995,检出限为 0.095 μg/g.方法简单,快速,损失少.应用此法测定4个核石墨样品(纯度为 99.999%),加标回收率为 97.2%～103.1%, 实验结果令人满意.