Institutional Repository of Institute of Modern Physics, CAS
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Gas-phase isothermal chromatography with short-lived technetium isotopes
No full textIn order to study the gas-phase chemical behavior of transactinides, an on-line isothermal chromatography apparatus has been developed and applied to separate short-lived technetium isotopes in the form of TcO3 from fission products. The fission products from a Cf-252 source were continuously and rapidly transported through the capillary to the isothermal chromatography apparatus using the N-2/KBr gas-jet techniques. Volatile oxide molecules were formed at the reaction zone kept at 900 degrees C since a trace amount of oxygen existed in the N-2 carrier gas. With the new developed isothermal chromatography apparatus, a selective separation of Tc from fission products was achieved. After isothermal chromatographic separation, Tc-101,Tc-103,Tc-104,Tc-105,Tc-106,Tc-107,Tc-108 were dominantly observed together with their Ru daughters in the gamma-spectrum, The chemical yields of Tc-101, and Tc-104 and Tc-105 isotopes with longer half-lives are about 55-57%, and those of Tc-103, Tc-106 and Tc-108 isotopes with shorter half-lives dropped down to 25-28%. The adsorption enthalpy of the investigated compounds on quartz surfaces was determined to be -150 +/- 5 kJ/mol by fitting the measured retention curves with a Monte Carlo model. The observed species of technetium oxide is attributed to TcO3, which is in good agreement with previous experimental results. That means our system worked properly and it can be used to investigate the gas-phase chemical behavior of transactinides
Segmented All-Platinum Nanowires with Controlled Morphology through Manipulation of the Local Electrolyte Distribution in Fluidic Nanochannels during Electrodeposition
No full textSynthesis of segmented all-Pt nanowires is achieved by a template-assisted method. The combination of a suitably chosen electrolyte/template system with pulse-reverse electrodeposition allows the formation of well-defined segments linked to nanowires. Manipulation of the morphology is obtained by controlling the electrokinetie effects on the local electrolyte distribution inside the nanochannels during the nanowire growth process, allowing a deviation from the continuously cylindrical geometry given by the nanoporous template. The length of the segments can be adjusted as a function of the cathodic pulse duration. Applying constant pulses leads to segments with homogeneous shape and dimensions along most of the total wire length. X-ray diffraction demonstrates that the preferred crystallite orientation of the polycrystalline wires varies with the average segment length. The results are explained considering transitions in texture formation with increasing thickness of the electrodeposit. A mechanism of segment formation is proposed based on structural characterizations. Nanowires with controlled segmented morphology are of great technological importance, because of the possibility to precisely control their substructure as a means of tuning their electrical, thermal, and optical properties. The concept we present in this work for electrodeposited platinum and track-etched polycarbonate membranes can be applied to other selected materials as well as templates and constitutes a general method to controlled nanostructuring and synthesis of shape controlled nanostructures
MEASUREMENT OF THE PROTON-PROTON CORRELATION FUNCTION FROM THE BREAK-UP OF Mg-22 AND Ne-20
No full textAn experiment of Mg-22 and Ne-20 beams bombarding on a C-12 target at an energy of 60 similar to 70 A MeV has been performed at the RIKEN projectile fragment separator (RIPS)in the RIKEN Ring Cyclotron Facility to study the two-proton correlated emission from Mg-22 and Ne-20 excited states. The two-protons momentum correlation functions have been obtained for Mg-22 and Ne-20, respectively. The trajectories of the Mg-22 decayed products (Ne-20 + p + p) were also measured to get the angular correlations between the two protons in Center of Mass of decaying system by relativistic-kinematics reconstruction. The results exhibit that Mg-22 has the features of He-2 cluster decay mechanism
Quench Protection Design and Simulation of a 7 Tesla Superconducting Magnet
No full textA 7 Tesla superconducting magnet with a clear warm bore of 156 mm in diameter has been developed for Lanzhou Penning Trap at the Institute of Modern Physics for high precision mass measurement. The magnet is comprised of 9 solenoid coils and operates in persistent mode with a total energy of 2.3 MJ. Due to the considerable amount of energy stored during persistent mode operation, the quench protection system is very important when designing and operating the magnet. A passive protection system based on a subdivided scheme is adopted to protect the superconducting magnet from damage caused by quenching. Cold diodes and resistors are put across the subdivision to reduce both the voltage and temperature hot spots. Computational simulations have been carried in Opera-quench. The designed quench protection circuit and the finite element method model for quench simulations are described; the time changing of temperature, voltage and current decay during the quench process is also analysed
A 3 Tesla Superconducting Magnet for Hall Sensor Calibration
No full textA 3 T superconducting magnet with a 70 mm diameter warm bore and energy storage of 47 kJ has been successfully fabricated and tested, which can be used to calibrate Hall sensors in high magnetic field as well as conduct superconducting experiments. The magnet consists of three solenoid coils and an iron yoke. The homogeneity of the magnetic field in the region of interest (ROI) is +/- 6.0 x 10(-5). The coils of the magnet were fabricated with NbTi-Cu superconducting wire and the stray magnetic field is shielded by an iron yoke. The coils and yoke are fully immersed in a helium vessel. The optimized structural design, stress and quench simulation, fabrication and test results are presented in this paper
New parameters of many-body potentials: studying the thermal and mechanical properties of noble metals
No full textNew parameters of nearest-neighbor EAM (1N-EAM), n-th neighbor EAM (NN-EAM), and the second-moment approximation to the tight-binding (TB-SMA) potentials are obtained by fitting experimental data at different temperatures. In comparison with the available many-body potentials, our results suggest that the 1N-EAM potential with the new parameters is the best description of atomic interactions in studying the thermal expansion of noble metals. For mechanical properties, it is suggested that the elastic constants should be calculated in the experimental zero-stress states for all three potentials. Furthermore, for NNEAM and TB-SMA potentials, the calculated results approach the experimental data as the range of the atomic interaction increases from the first-neighbor to the sixth-neighbor distance
RFQ 冷却聚束器 RFQ1L的研制
No full textRFQ冷却聚束器是目前国际上核物理研究领域中常用的一种束流操控手
段，现已经被用于中国科学院近代物理研究所正在研制的重核及核结构研究
谱仪SHANS 和精密质量测量彭宁离子阱LPT中。SHANS的最终目标是对熔
合蒸发反应产生的远离β稳定线的奇异核进行电荷数Z和质量数A的直接指定，
而LPT是对原子核质量进行高精度的测量。通过RFQ冷却聚束器，我们可以有
效地降低核反应产生的放射性束流的能散、发射度和束斑，高速高效地提高束
流品质。由于这些产物的反应产额非常低，出射束流品质很差，对余核的操控
非常困难，因此RFQ冷却聚束器的研制难度也非常大。
本论文的工作以RFQ1L的模拟、机械设计、加工装配及离线调试为主要内
容。受计算机硬件的限制，RFQ1L的模拟分为冷却约束段和束流引出段两部分
进行。通过模拟研究，获得了和原理一致的结论，了解了离子在冷却约束段的
运动情况，为机械设计及调试提供了参考。
从机械加工原材料的选择开始，详细讲述了RFQ1L的机械结构、零部件加
工要求及总体装配过程。除主体部分之外，RFQ1L还需要相应的配套系统，包
括真空系统、气压控制系统、离线调试所需离子源及其束流传输线、离子引出
系统、供电系统及探测器等。文中也对其进行了详细的介绍，讲述了各部分的
原理及测试结果。
离线调试是设备建设的一个必需环节。论文首先阐述了缓冲气体高压击穿
的实验测试，离子源及其传输线的调试，以及通过浮动电压来调节离子入射能
量方面的测试。然后，细致论述了高频电场的电压及频率、缓冲气体压强、轴
向电场引导、不同离子能量等对离子冷却约束的作用和影响，获得了很重要的
调试结果，即：我们已经成功调试了专用的测试离子源、束流传输和差分系
统，观察到缓冲气体的降能和阻止作用、RF电场的约束作用和轴向电场的引
导作用。
作为阶段性成果，本论文的工作将为后续的在线调试提供重要的指导及参
考
The Magnetic Field Optimization Design ofa 7T highly homogeneous SuperconductingMagnet for Lanzhou Penning Trap
No full textPenning 离子阱是当前核物理研究的重要装置之一，是当前原子核质量测
量精度最高的装置;迄今为止，最精确的原子核质量都是通过Penning离子阱获
得的。精密的质量测量不仅具有重大的科学意义，而且由于 Penning 离子阱的
研制涉及到仿真计算、超导技术、机械设计和制造、电子学控制、计算机编程
等诸多方面，因此其研制的本身也是一个国家总体科技发展水平的标志之一，
目前，只有美国，加拿大，西欧和北欧的一些科技发达国家建立了 Penning 离
子阱。兰州Penning离子阱（Lanzhou Penning Trap,简称LPT）是中国科学院
近代物理研究所自主开发研制的用于高精度质量测量的 Penning 离子阱系统，
LPT的主要目的是测量由熔合蒸发反应产生的放射性核素的质量，并在可能的
条件下对超重核的质量进行直接的精确测量，预期达到的质量分辨率为10−7。
在 LPT 装置中，超导磁体系统是一个重要的组成部分，其性能的优劣是
决定离子阱测量精度的主要指标。该超导磁体在直径为 156 mm的温孔中产生
用于安放离子阱的两个均匀场区，均匀度好于 0.5 ppm，轴向相距 22 mm，且
要求很好的磁屏蔽以保证低漏场，因此对超导磁体的设计和制造提出了非常高
的要求。本论文对高均匀度超导磁体系统的优化设计方法进行了深入的研究。
研究内容涉及到超导磁体的磁场优化、超导磁体的加工误差与不确定性分析、
无源匀场优化等，主要包括几个方面：
1. 主磁体优化设计
提出了一种两步优化设计方法，首先利用线性规划算法进行拓扑优化，
获得线圈最优形状，然后将通用优化软件 DAKOTA 与磁场计算软件结
合，利用非线性优化算法对线圈形状进行简化。利用这一优化设计方法，
设计出了满足LPT磁场要求的主动屏蔽型高均匀度超导磁体。
2. 加工误差和不确定性分析
利用拉丁超立方采样方法对磁体的加工误差等进行了全局不确定性分析，
评估了磁体优化设计方案的稳健性和可靠性。
3. 无源匀场优化设计
设计了用于修正加工误差等所带来的不均匀磁场分量的无源匀场系统，
基于线性规划方法和积分方程法开发了无源匀场软件，提出了基于匀场
片面积的精细匀场方法，并利用磁场仿真软件 Radia 对无源匀场过程进
行了仿真，仿真结果表明，由于加工误差等原因导致的上千 ppm 的磁场
不均匀度能够通过该匀场方法修正到几个ppm的量级
VACUUM SYSTEM OF HIRFL’S CYCLOTRONS
No full textHIRFL has 2 cyclotrons: a sector focus cyclotron (SFC)<br />and a separate sector cyclotron (SSC). SFC was built in<br />1957. In the past 50 years, the vacuum system of SFC has<br />been upgraded for three times. The vacuum chamber was<br />redesigned to double-deck at the third upgrade. The<br />working pressure in beam chamber was improved from<br />10-6mbar to 10-8mbar. SFC has delivered Pb, Bi and U<br />beams in the past few years since the last upgrading of its<br />vacuum chamber. SSC began to operate in 1987. The<br />vacuum chamber of SSC has a volume of 100m3. 8<br />cryopumps keep the pressure from 5×10-7mbar to 8×10-<br />8mbar depending on the used pump numbers (2~8). In the<br />past 20 years, because of the contamination of oil vapour<br />and leaks occurred in some components inside the SSC<br />vacuum chamber, the vacuum condition has worsened<br />than the beginning. It is a big problem to accelerate the<br />heavier ions. The upgrade for the SSC vacuum system<br />will be an urgent task for us. The rough pumping systems<br />of both SFC and SSC have been rebuilt recently. As a<br />result, the oil vapour in two cyclotrons will be eliminated<br />and the vacuum condition of them will be improved.<br />A new small cyclotron will be built in HIRFL as an<br />injector of the Heavy Ion Therapy Facility in Lanzhou<br />(HITFiL). The brief introduction of the vacuum system<br />design is given in the paper
STATUS OF THE HZB# CYCLOTRON: EYE TUMOUR THERAPY IN BERLIN
No full textThe mission of the ion beam laboratory<br />(Ionenstrahllabor) ISL was the provision of fast ions for<br />solid state physics, materials analysis and medical<br />applications in basic as well as applied research. Eye<br />tumours are treated since 1998 with 68 MeV protons in<br />collaboration with the University Hospital Benjamin<br />Franklin, now Charité - Campus Benjamin Franklin. In<br />autumn 2004 the board of directors of the HMI decided to<br />close down ISL at the end of 2006. In December 2006, a<br />cooperation contract between the Charité and the HMI<br />was signed to assure the continuity of the eye tumour<br />therapy, at this moment being the only facility in Germany.<br />We have now experienced the first three years under<br />the new boundary conditions; treating more than 600<br />patients in that time. The main challenge is to supply<br />protons for the therapy with less man-power but keeping<br />the same high reliability as before. The conversion<br />process is not yet finished. The installation and<br />commissioning of a new, facile injector for protons will<br />be discussed. In addition to the routine treatment, proton<br />therapy of ocular tumours for very