加速器-电镜联机的离子光路及其调整方案

离子辐照引起的材料微结构变化是一个复杂的过程,用加速器-电镜联机装置可原位观察载能离子束辐照引起的材料微结构演变.武汉大学加速器-电镜联机装置由1台2×1.7 MV串列加速器、1台200 kV离子注入机和1台200 kV透射电镜组成,通过自行设计的传输系统实现联机.本文介绍联机装置的光路布局,给出了静电加速器离子动力学计算程序LEADS(linear and electrostatic accelerator dynamics simulation)优化计算的结果,提出了两种改进方案,并用LEADS对改造后的加速器-电镜联机中离子运动进行了计算.结果显示,调整现光路二单元四极透镜的同时,在200 kV注入机90°偏转磁铁至电镜之间增加1个二单元静电四极透镜,将提高该系统中离子束传输效率.     

直通道磁元件磁场测量

为使重离子束从注入器（ＳＦＣ）不经主加速器（ＳＳＣ）直接传输到实验终端。最近在兰州重离子研究装置（ＨＩＲＦＬ）上新建了直通管道系统。在该系统中有３台偏转磁铁和３台四极透镜。本文叙述了它们的测磁内容和方法，给出了激磁曲线、径向和轴向场分布、磁场梯度、等效长度等结果。结果表明：全部符合原设计要求，并有一定的余量。     

千兆电子伏重离子加速器——兰州冷却储存环

能量达千兆电子伏的兰州重离子加速器冷却储存环HIRFL-CSR,是一个集加速、累积、电子冷却及内外靶实验于一体的多功能双冷却储存环同步加速器系统,由主环CSRm和实验环CSRe构成,并以兰州重离子回旋加速器系统HIRFL作注入器。CSR将重离子束的能量从兆电子伏提高到千兆电子伏,同时利用空心电子束冷却技术将束流的动量分散及发射度降低1~2个数量级,并提供多种类的高电荷态重离子束以及放射性次级束(RIBs),以开展更高精度的物理实验及更广范围的应用研究。兰州冷却储存环于2006年建成并投入运行,实现了剥离注入与多圈注入、空心电子束对重离子束的冷却与累积、变谐波宽能区同步加速、等时性环型谱仪、RIBs的产生与收集以及重离子束的快慢引出,并实现了高能重离子束的空心电子束冷却,使得重离子束的动量分散降低到10^-5量级,而发射度收缩到0.1πmm•mrad以下。同时,完成了短寿命近滴线核素的高分辨质量测量物理实验及高能重离子束深层治癌的临床应用实验。     

HL-2中性束注入器离子束系统的设计计算

在受控核聚变研究中,中性束注入已经成为加热等离子体的有效手段。中性束注入器的关键部分是离子束系统,它的性能决定了中性束注入的效率和效果。文章就大功率中性束注入器离子源及离子引出、加速系统主要工作参数的设计计算方法进行了论述,并给出了HL-2装置中性束注入器离子束系统的计算结果。在强流离子束引出、加速系统束光学特     

强流氘束引出系统与加速管束流匹配的研究

为增加传输通过加速管的束流强度,提高中子发生器的中子产额,采用Particle-in-cell(PIC)程序模拟研究了入射束强度在10～150 mA范围内,不同初始参数条件下D⁺₁束在加速管中的传输状态。结果表明,当入射束在加速管入口处的归一化发射度取0.25 πcm•mrad,Courant-Snyder参数α=-4、β=60 cm/rad时,50～100 mA D⁺₁束与加速管匹配良好。根据匹配参数,对双等离子体离子源的引出系统进行了优化,结果显示,在引出系统与加速管之间放置两个螺线管透镜和1个光阑,能有效去除D⁺₂、D⁺₃离子,实现100 mA D⁺₁束顺利传输通过加速管的目的。     

基于静电分析器的全自动高精度能谱测量系统

本文实现了一种基于静电分析器的全自动高精度能谱测量系统,并成功用于微团簇离子束同石墨烯薄膜相互作用的实验研究。基于该高精度能谱测量系统,研究了1.8 MeV的H⁺₂微团簇同4层石墨烯薄膜的相互作用过程,测量了库仑爆炸后的质子能谱和透射的H⁺₂能谱,实现了全自动的能谱采集,极大提高了数据获取速度,降低了实验误差。测量结果表明,该系统在H⁺₂的入射能量1.8 MeV处的能量分辨约为0.6 keV,对于下一步开展基于加速器的高精度能谱测量研究具有重要意义。     

双离子束实验装置离子光学系统的计算机辅助设计

本文扼要介绍了一台双离子束实验装置离子光学系统的计算机辅助设计。该设计用传输矩阵方法和TRANSPORT程序完成。     

HL-2中性束注入器离子束系统的设计计算

在受控核聚变研究中,中性束注入已经成为加热等离子体的有效手段。中性束注入器的关键部分是离子束系统,它的性能决定了中性束注入的效率和效果。文章就大功率中性束注入器离子源及离子引出、加速系统主要工作参数的设计计算方法进行了论述,并给出了HL-2装置中性束注入器离子束系统的计算结果。在强流离子束引出、加速系统束光学特性的数值计算程序中,考虑了离子源等离子体参数、等离子体弥散电子及离子束内部空间电荷效应对束光学性能的影响。计算表明,对于设定的55kev,80A的离子束系统,氢和氘离子束的匹配流密度分别为0.22A·cm~(-2)和0.155A·cm~(-2)。     

N+离子注入技术在中性蛋白酶高产

为获得中性蛋白酶高产菌株,选用低能（30keV）N⁺离子束以不同剂量注入中性蛋白酶,产生菌枯草芽孢杆菌（Bacillussubtilis）AS1.398,研究其诱变效应,菌株存活率曲线为典型的“马鞍型”剂量 效应曲线,且在马鞍形区域内具有较高的正突变率。经多次筛选,获得一株稳定高产突变株ZC-12,突变株产中性蛋白酶活力为初始菌株的1.84倍。通过对PCR扩增诱变前后两菌株编码中性蛋白酶基因的DNA序列的测序和比对,在所报道的该酶催化区域内,有3个氨基酸位点发生突变,表明N⁺离子束注入细胞的辐射诱变方法具有独特的诱变效果,可用于菌种选育。     

200keV离子束生物工程装置的研制

离子束生物诱变研究是不同于传统辐射生物学的一门新兴学科。目前，我国在这方面的研究尚处于世界领先地位。本文报导了一台用于离子束生物诱变研究的２００ｋｅＶ离子束装置。该装置对强流离子束采用先分析后加速的总体设计方案，一台热阴极来复式弧放电双等离子源用于产生Ｈ、Ｎ、Ｏ、Ｃ、Ｐ和Ｆｅ、Ｃｕ、Ｚｎ等离子，最大靶流１０ｍＡ（Ｎ＋）。本文给出了这台装置的详细结构、物理设计参数和运行参数     

BRISOL钠同位素放射性核束的产生

北京放射性核束装置在线同位素分离器（BRISOL）采用100 MeV、200 μA回旋加速器提供的质子束打靶产生中、短寿命放射性核束,在线分析后供物理用户使用,其质量分辨率好于20 000。为开展²⁰Na核的奇异衰变特性研究,研制了氧化镁靶,并采用100 MeV质子束轰击氧化镁靶在线产生了^20～26Na⁺的钠同位素放射性核束。当质子束流强为8 μA时,²⁰Na⁺离子束的最大产额为2×10⁵ s^-1,²¹Na⁺离子束的最大产额为4×10⁸ s^-1。完成了北京放射性核束装置首个放射性核束物理实验,累计供束近200 h。     

北京放射性核束装置在线同位素分离器的研制

北京放射性核束装置在线同位素分离器（BRISOL）采用100 MeV、200 μA回旋加速器提供的质子束打靶产生中、短寿命放射性核束,进行在线分析后供物理用户使用,其质量分辨率好于20 000。BRISOL装置现已建成,并开展了氧化镁、氧化钙靶的在线实验,在线产生了³⁷K⁺、³⁸K⁺、²⁰Na⁺、²¹Na⁺等多种放射性核束。本文详细介绍该装置的研制及运行情况。     

Synthesis of carbon-nitride films using a fast-switched dual-source low energy ion beam deposition system

Thin C_xN_y films were deposited in UHV using alternating low energy ion beams of C⁺ and N⁺ or N₂⁺ in the energy range of 5 to 100 eV. The ion beam deposition system is equipped with two Freeman ion sources, mass analysis and fast automated beam switching, allowing perpendicular bombardment of the target with a single ion beam at a time. The composition and density of the films were studied by ARS (in situ), XPS and RBS. The dependence of the film properties and growth mechanisms on ion energy, beam switching rate, and C-to-N arrival ratio have been investigated. The influence of the deposition parameters on the film stoichiometry is discussed. Exposure of the film to atmosphere leads to oxygen incorporation, resulting in a lowered surface concentration of nitrogen. The XPS N 1s and C Is binding energies vary in a relatively broad range indicating that several bond states may be present. The influence of the substrate material on film growth has also been studied. On Si{100}, film growth commences with the formation of an interfacial silicon nitride. No film growth was observed on gold, however deposition was possible on tantalum and molybdenum.     

A dual ion beam epitaxy system

The design and characteristics of a dual ion beam epitaxy system (DIBE) are discussed. This system is composed of two beam lines, each providing a mass-separated ion beam converging finally with the other into the target chamber. The ions are decelerated and deposited on a substrate which can be heated to a temperature of 800°C. Currents of a few hundred microampères are available for both beams and the deposit energies are in the range from tens to 1000 eV. The pressure of the target chamber during processing is about 7 × 10⁻⁶ Pa. Preliminary experiments have proved that compound semiconductor materials such as GaN can be synthesized using the DIBE system.     

含杂质的卢瑟福散射的蒙特卡罗模拟

采用蒙特卡罗方法数值研究了杂质对α粒子卢瑟福散射的影响。杂质原子根据靶材的纯度以给定的概率随机替换靶材原晶格的原子。研究结果表明,考虑杂质后,出射粒子随散射角分布的曲线中形成了新的峰,峰的位置随杂质元素原子序数的增加向大角度方向移动;杂质的原子序数越低、含量越高,对卢瑟福散射出射粒子角分布的影响越明显;同时,入射粒子能量越低,杂质产生的峰对分布曲线的影响越明显。此外,对典型的C6+、N7+等重离子束的卢瑟福散射的模拟计算结果表明,重离子束对杂质有更好的分辨率。     

北京大学4.5 MV静电加速器核反应分析系统

为满足对聚变堆面向等离子体材料中氘氚滞留问题的研究,北京大学4.5 MV静电加速器在原束线基础上新增核反应分析系统,该系统使用能量0.8～3.6 MeV的H⁺、D⁺、³He⁺和⁴He⁺粒子束流,可对核反应微分截面和样品中元素浓度的深度分布进行测量分析。本文对核反应分析原理、核反应分析系统的设备布局和实验方法进行了讨论,并以D(³He,p)⁴He核反应为例,分析了微分截面计算和样品中氘元素浓度深度分布的数据结果,其深度分辨小于1.5 μm,实验误差约为7.5%。     

The development of a time of flight spectrometer for LARN

An elastic recoil detection time of flight system to depth profile light elements has been developed on ALTAÏS, the new Tandetron accelerator at LARN. The detector mounted at 45° from the beam axis consists of two isochronous electron detectors for the timing signal (START and STOP) and a 450 mm² heavy ion PIPS detector that detects the energy of the recoil atoms. The 2MV Tandem accelerator provides heavy ion beams with a maximum energy of 16 MeV depending on the charge transfer efficiency of the gas exchange canal located in the middle of the machine. A large variety of primary ion beams like ²⁸Si, ³⁵Cl, ⁶³Cu, ¹²⁷I or ¹⁹⁷Au can be produced with the SINIX heavy ion source and accelerated on the target. Typical current around 1 nA can be obtained. The energy transfer to the recoil atoms is typically in the MeV range and depends on the mass and the energy of the projectile. Some secondary effects like the energy loss in the carbon foils of the timing detector but also in the entrance window of the energy detector should not be neglected if we try to depth profile light elements with this technique. Time resolution of about 1 ns for the electrons detectors is suitable to obtain 1 amu mass resolution. Some examples of applications will be developed in this paper.     

A new concept kinetic-ejection negative-ion source for rib generation

Chemically active radioactive species are often released from target-materials in a variety of molecular forms. For example, ¹⁷F, is principally released from Al₂O₃ target-material as Al¹⁷F. Because of the low probability of simultaneously dissociating such molecular carriers and efficiently ionizing their atomic constituents with conventional hot-cathode, electron-impact ion sources, species of interest are often distributed in several mass channels in the form of molecular side-band beams. Consequently, beam intensities of the desired radioactive species are diluted. The sputter negative-ion beam generation technique is particularly effective for simultaneously dissociating molecular carriers and efficiently ionizing highly electronegative atomic constituents. Therefore, a new concept kinetic-ejection negative-ion source (KENIS), based on this principle, was conceived to address this problem. The source has proven to be highly efficient for simultaneously dissociating and negatively ionizing sputter-ejected atomic fluorine from cesiated surfaces. The source has been successfully employed on-line to generate high intensity ¹⁷F⁻ beams for use in the astrophysics research program at the Holifield Radioactive Ion Beam Facility (HRIBF) using the ¹⁶O(d,n)¹⁷F reaction. The mechanical design features, principles of operation, operational parameters, beam quality information (emittance data) and efficiencies for forming intense beams of ¹⁷F⁻ during off-line and on-line operation of the source are presented in this report.     

Capture by Highly-Charged Low-Energy Ions Studied with a Secondary Ion Recoil Source

When a highly-charged fast projectile collides with a neutral atom in a gaseous target it may, in a single collision, remove many electrons from the target while transferring no more than a few eV to the target's center of mass. These low-energy highly-charged (LEHQ) recoils may be extracted for use as a secondary ion beam to study subsequent capture reactions in a second gas target. We have developed a LEHQ ion source based on this principle, pumped by 1-2 MeV/amu beams of F, S and Cl. In this paper we discuss 1) the properties of the ion source, and 2) cross sections measured with the source for single and multiple electron capture by Ar+q from Ne for 2 < q < 10 and Ar energies between 200 and 1000 eV per q.