Design studies on the 4 pi gamma-ray calorimeter for the ETF experiment at HIRFL-CSR

A high detection efficiency calorimeter which is used to detect gamma-rays with energies from 1 MeV up to 10 MeV as well as light charged particles has been proposed. Design of the geometry, results of the crystal tests and Monte Carlo simulations are presented in this paper. The simulation results confirm that the calorimeter can obtain high detection efficiency and good energy resolution with the current designed geometry. And the calorimeter is competent for the future External Target Facility (ETIF) experiments.

Electron impact excitation rate coefficients of N II ion

This paper calculates the electron impact excitation rate coefficients from the ground term 2s(2)2p(2) P-3 to the excited terms of the 2s(2)2p(2), 2s2p(3), 2s(2)2p3s, 2s(2)2p3p, and 2s(2)2p3d configurations of N II. In the calculations, rnulticonfiguration Dirac-Fork wave functions have been applied to describe the target-ion states and relativistic distorted-wave calculation has been performed to generate fine-structure collision strengths. The collision strengths are then averaged over a Maxwellian distribution of electron velocities in order to generate the effective collision strengths. The calculated rate coefficients are compared with available experimental and theoretical data, and some good agreements are found for the outer shell electron excitations. But for the inner shell electron excitations there are still some differences between the present calculations and available experiments.

Influence of core property on multi-electron process in slow collisions of isocharged sequence ions with neon

Influence of core property on multi-electron process in the collisions of q = 6-9 and 11 isocharged sequence ions with Ne is investigated in the keV/u region The cross-section ratios of double-, triple-, quadruple- and total multi-electron processes to the single electron capture process as well as the partial ratios of different reaction channels to the relevant multi-electron process are measured by using position-sensitive and time-of-flight techniques The experimental data are compared with the theoretical predictions including the extended classical over-barrier model, the molecular Columbic barrier model and the semi-empirical scaling law Results show a core effect on multi-electron process of isocharge ions colliding with Neon, which is consistent with the results of Helium we obtained previously

Theoretical study of the 4d photoabsorption of the Cs+ ion

Calculations of the 4d absolute photoabsorption cross sections of the Xe-like Cs+ ion covering the energy region from 80 to 190 eV have been performed by using the multi-configuration Dirac-Fock method. The calculated cross sections are compared with the absolute experimental photoabsorption cross-section spectrum (Kjeldsen et al 2002 J. Phys. B: At. Mol. Opt. Phys. 35 2845) and other available theoretical results. In the 80-90 eV region, the discrete structure resulting from photoexcitation of a 4d electron into nf and np orbits are successfully identified. Above the 4d threshold, i.e. in the 90-190 eV energy region, a reasonable agreement between experiment and computations is found for the intense 4d -> epsilon f shape resonance.

Two Electron Transfer and Stabilization in Slow O6+ and Rare-Gas Collisions

The stabilization ratios.. for double-electron transfer, i.e., the cross section ratios of true double capture to total double-electron transfer, are measured in O6++ He, Ne and Ar collisions at 6 keV/u. A high.. value about 68% is obtained for the He target, while for the Ar target, the.. value is only 8%. The high R value for the He target is due to the significant direct population of the (2l, nl') configurations with high n For the Ar target, the (quasi) symmetric configurations (3l, nl') lead to the much lower.. value. Neglecting the core effects, the O6+ ion can be taken as a bare ion C6+ except the occupied 1s shell, and then the measured R values are compared with previous experimental results of C6+ projectile ions at similar impact velocity. It yields good agreement with the Ne and Ar target, while the occupied 1s shell for the O6++ He system results in a higher R value than that in C6++He collisions.

X-ray spectrum emitted by the impact of Xe-129(q+) on Mo surface

We studied the characteristic X-ray spectra produced by the interaction of highly charged ions of X-129(q+) (q =25, 26, 27) with surface of metallic Mo. The experimental result shows that highly charged ions can excite the characteristic X-ray spectra of L-shell of Mo when the beam' s intensity is not more than 120 nA. The X-ray yield of single ion reaches a quantitative level of 10(-8) and increases with the increment of the ion' s kinetic energy and ionic charge (potential energy). By measuring the X-ray spectra of Mo-L alpha(1) the M-level lifetime of Mo atom is estimated by using Heisenberg uncertainty relation.

New development of advanced superconducting electron cyclotron resonance ion source SECRAL (invited)

Superconducting electron cyclotron resonance ion source with advance design in Lanzhou (SECRAL) is an 18-28 GHz fully superconducting electron cyclotron resonance (ECR) ion source dedicated for highly charged heavy ion beam production. SECRAL, with an innovative superconducting magnet structure of solenoid-inside-sextupole and at lower frequency and lower rf power operation, may open a new way for developing compact and reliable high performance superconducting ECR ion source. One of the recent highlights achieved at SECRAL is that some new record beam currents for very high charge states were produced by 18 GHz or 18+14.5 GHz double frequency heating, such as 1 e mu A of Xe-129(43+), 22 e mu A of Bi-209(41+), and 1.5 e mu A of Bi-209(50+). To further enhance the performance of SECRAL, a 24 GHz/7 kW gyrotron microwave generator was installed and SECRAL was tested at 24 GHz. Some promising and exciting results at 24 GHz with new record highly charged ion beam intensities were produced, such as 455 e mu A of Xe-129(27+) and 152 e mu A of Xe-129(30+), although the commissioning time was limited within 3-4 weeks and rf power only 3-4 kW. Bremsstrahlung measurements at 24 GHz show that x-ray is much stronger with higher rf frequency, higher rf power. and higher minimum mirror magnetic field (minimum B). Preliminary emittance measurements indicate that SECRAL emittance at 24 GHz is slightly higher that at 18 GHz. SECRAL has been put into routine operation at 18 GHz for heavy ion research facility in Lanzhou (HIRFL) accelerator complex since May 2007. The total operation beam time from SECRAL for HIRFL accelerator has been more than 2000 h, and Xe-129(27+), Kr-78(19+), Bi-209(31+), and Ni-58(19+) beams were delivered. All of these new developments, the latest results, and long-term operation for the accelerator have again demonstrated that SECRAL is one of the best in the performance of ECR ion source for highly charged heavy ion beam production. Finally the future development of SECRAL will be presented.

TIME-DEPENDENT DENSITY FUNCTIONAL STUDY OF MULTIELECTRON TRANSFER IN Cq+-Na-4 COLLISIONS

The process of multielectron transfer from a Na-4 cluster induced by highly charged C6+, C4+, C2+ and C+ ions is studied using the method of time-dependent density functional theory within the local density approximation combined with the use of pseudopotential. The evolution of dipole moment changes and emitted electrons in Na-4 isobtained and the time-dependent probabilities with various charges are deduced. It is shown that the Na-4 cluster is strongly ionized by C6+ and that the number of emitted electrons per atom of Na-4 is larger than that of Na-2 under the same condition. One can find that the detailed information of the emitted electrons from Na-4 is different from the same from Na-2, which is possibly related to the difference in structure between the two clusters.

Some Superconducting Magnets at IMP

Some superconducting magnets research at IMP (Institute of Modern Physics, CAS, Lanzhou) will be described in this paper. Firstly, a superconducting electron cyclotron resonance ion source (SECRAL) was successfully built to produce intense beams of highly charged heavy ions for Heavy Ion Research Facility in Lanzhou (HIRFL). An innovation design of SECRAL is that the three axial solenoid coils are located inside of a sextupole bore in order to reduce the interaction forces between the sextupole coils and the solenoid coils. For 28 GHz operation, the magnet assembly can produce peak mirror fields on axis of 3.6 T at injection, 2.2 T at extraction, and a radial sextupole field of 2.0 T at plasma chamber wall. Some excellent results of ion beam intensity have been produced and SECRAL has been put into operation to provide highly charged ion beams for HIRFL since May 2007. Secondly, a super-ferric dipole prototype of FAIR Super-FRS is being built by FCG (FAIR China Group) in cooperation with GSI. Its superconducting coils and cryostat is made and tested in the Institute of Plasma Physics (IPP, Hefei), and it more 50 tons laminated yoke was made in IMP. This super-ferric dipole static magnetic field was measured in IMP, it reach to the design requirement, ramping field and other tests will be done in the future. Thirdly, a 3 T superconducting homogenous magnetic field solenoid with a 70 mm warm bore has been developed to calibrate Hall sensor, some testing results is reported. And a penning trap system called LPT (Lanzhou Penning Trap) is now being developed for precise mass measurements.

近玻尔速度高电荷态离子与表面作用诱发的溅射离子能谱

近玻尔速度高电荷态离子在物质表面诱发的溅射离子能谱研究在理论和实验上尚是一片空白。本工作针对溅射离子能谱测量，设计、建立了一台径向位置灵敏127o柱形静电离子能谱仪。该谱仪结合位置灵敏探测器，克服了传统静电谱仪只能通过扫描电场单次、单能量点取谱的缺陷，实现了分段取谱——单次可获取宽为0.85Ec ≤ E ≤ 1.15Ec的能谱，极大提高了实验测量效率。利用该谱仪，首次获得了0.8至1.8倍玻尔速度Ar7，8，9+离子与金属铍靶和高定向性石墨靶碰撞产生的溅射离子能谱（入射角45o ，出射角135o）。结果表明：1）能谱分布很宽，其峰值位于130eV至600eV之间，远大于线性级联碰撞区的几到十几eV；且峰位随入射离子速度增加向高能方向略有移动。2）铍靶的溅射能谱呈一个极不对称的峰分布——高能部分有很长的尾巴，下降趋势服从E-n分布；其能谱与入射离子速度关联很大，小于vBohr时指数n与线性级联碰撞接近，而大于vBohr时非线性贡献明显。3）石墨靶的能谱峰位与入射离子动能、势能相关；其谱形在上升到最大值后均出现一个很宽的平台，表明该系列碰撞系统中，非线性效应占主导

高性能小型带电粒子探测阵列的研制

随着核物理理论研究和各种先进探测设备研制工作的不断深入,世界各大实验室相继建立了各具特色的放射性束装置,放射性束物理得到了长足的发展。在放射性束引起的核反应实验上,要得到更加精确的非稳定原子核的结构信息和反应机制，需要对反应产物实现完全运动学测量,这就要求位置分辨和能量分辨更精确的探测器装置。高性能小型带电粒子探测阵列是基于△E-E粒子鉴别方法,采用位置分辨精确的双面硅微条作为△E探测器,用阻止本领大的BGO晶体阵列作为E探测器,来测量反应产物的能量分辨和角分布,从而进行带电粒子的鉴别。 Geant4是由欧洲核子中心(CERN)开发的一个大型高能物理探测器模拟程序，是采用当代先进的面向对象程序设计技术利用C++语言编写的。我们基于该模拟工具,对探测器分辨随能量的变化情况、粒子斜入射对探测器分辨的影响情况、晶体厚度变化对分辨的影响情况以及与阻止相同能量的CsI晶体分辨情况等进行了一系列的模拟对照。 本论文工作的主要内容有:首先,介绍了探测器的研制及测试过程。该探测器用一块双面硅微条作为△E探测器,用64块BGO晶体阵列作E探测器。晶体阵列采用一块64单元位置灵敏的光倍管读出信号。该探测器具有体积小，死区小,位置分辨好等优点。其次,根据探测器在实验中可能遇到的问题,我们利用Geant4系统的模拟了晶体尺寸变化对分辨的影响情况；晶体分辨随能量升高的变化情况及粒子斜入射对晶体分辨造成的影响等，从而为探测器选用合适尺寸的晶体提供了很好的参考。模拟结果显示，晶体分辨随着能量升高而变好,这为选用BGO晶体作为带电粒子探测阵列提供了很好的参考；粒子斜入射会对分辨造成一定的影响，并从三维图上显示了粒子的踪迹，这为今后实验数据处理提供了很好的参考；与CsI晶体位置分辨和能量分辨作了对照模拟，模拟结果显示，随着带电粒子能量的增加BGO分辨逐渐与CsI晶体接近，并且角分辨会比CsI晶体好，从而得出BGO晶体用来作带电粒子探测阵列的独特优势。最后，针对以后的工作方向作了简单的讨论

高电荷态离子与固体表面作用的研究

高电荷态离子与固体表面相互作用研究不仅在原子结构和能级寿命，量子电动力学效应和等离子体物理等方面具有重要的基础研究价值，而且在表面分析和加工，短波辐射源开发等方面也有着潜在的应用价值。论文介绍了在兰州重离子加速器国家实验室ECR离子源上建成的用于高电荷态离子与固体表面作用研究的物理实验终端，研究了高电荷态离子与固体表面作用中的可见光和X射线发射以及高电荷态离子在固体表面引起的离子溅射产额和电子发射产额。研究了固体表面靶原子特征可见光谱和X射线的激发机制；分析了空心原子X射线谱的重要特征以及高电荷态离子动能沉积和势能沉积在表面离子溅射和表面电子发射中的作用

高电荷态238Uq+在碳膜中电荷平衡时间的研究

离子通过物质过程中与靶原子发生碰撞，碰撞中大量电子被俘获和电离。当电子俘获截面与电离截面达到平衡时，出射离子的电荷态分布达到一个平衡的分布，这个分布与入射离子的核电荷数、速度、壳层结构以及靶材料的性质有关。研究离子通过物质后的电荷态分布和电荷平衡时间对于研究高电荷态离子穿越物质层时的电荷转换及平衡过程具有重要意义。 本文论述了能量为0.8 MeV/u 238Uq+离子通过不同厚度碳膜后的电荷态分布，并对铀离子在碳膜中的电荷平衡时间进行了研究。 实验中束流采用兰州重离子加速器国家重点实验室（HIRFL）首次加速出的能量为0.8 MeV/u 238U26+离子束。本实验是首次在兰州放射性次级束流线（RIBLL）实验终端进行，采用的实验方法新颖。为了研究不同初始电荷态的铀离子通过不同厚度碳膜后的电荷态分布，实验中采取让初级束流 238U26+通过0.1µm厚度碳膜后形成一个电荷态分布，通过调节二极磁铁的控制电流从中选择某一电荷态轰击碳靶，进行电荷态分布研究。 实验对0.8 MeV/u 238Uq+(q=26，29，34，39)通过不同厚度碳膜（5µg/cm2，15µg/cm2，26µg/cm2和225µg/cm2）后的电荷态分布进行了研究。结果发现：能量为0.8 MeV/u的铀离子通过5µg/cm2厚度碳膜后，出射铀离子的电荷态分布未达到平衡；同样铀离子通过15µg/cm2厚度碳膜后，出射铀离子的电荷态分布已达到平衡，平衡平均电荷态为33.72+；由此通过计算得到铀离子在碳膜中的电荷平衡时间为1/3×5.4fs<=t<=5.4fs

高电荷态离子与固体表面作用的离子溅射和电子发射的实验研究

高电荷态离子与固体表面相互作用的研究是目前国际上广受关注的热点研究领域之一。本论文详细介绍了在兰州重离子加速器国家实验室ECR离子源上建成的高电荷态离子表面物理实验平台；着重叙述了在实验平台上完成的高电荷态离子在固体表面引起的离子溅射和电子发射的研究。我们用初动能Ek=216～720keV的高电荷态Pb36+离子和初动能为Ek=144～288keV的Arq+（q =11～16）离子以不同入射角度(Ψ＝15º～80º)作用于Nb、Si和SiO2表面，通过研究离子溅射产额与入射离子初动能、势能（电荷态）和入射角度的关系，得到了以下结论：离子溅射产额与炮弹离子的势能沉积和动能作用有关；对Ar离子，电荷态从11增加到16时，离子溅射产额是随之增长的。而对Pb36＋离子，表面离子溅射产额随入射离子初动能的变化关系跟核阻止能损随入射离子初动能的变化关系是一致的，离子溅射产额与核阻止能损是线性相关的。认为高电荷态引发的表面离子溅射过程是势能沉积作用与线性级联碰撞过程协同作用的结果。我们还测量了Heq+(q=1,2, Ek=12keV～48keV)，Neq+(q=2～8, Ek=18～192keV)，Arq+(q=3～12, Ek=72keV)离子垂直作用于Si, W, Au表面产生的电子发射产额。得到了纯粹势能电子发射产额与入射离子势能的定量关系，势能电子产额随入射离子势能的增加而线性增加，势能每增加1eV，单离子电子发射产额增加0.0088（以初动能为42keV的Neq+入射到W表面为例）。势能电子发射增量跟靶的性质有关，W表面对势能变化的响应最剧烈，其次是Si表面。通过引入纯粹动能电子产额与电子能损的比值B分析和研究了动能电子发射，随着入射离子原子序数和初动能的增加，B因子有缓慢降低的趋势；B因子与靶材料密切相关，Au靶的B因子明显大于Si靶和W靶；我们还首次把B因子的研究扩展到高电荷态离子领域，认为B因子与入射离子的势能（电荷态）无关

低速高电荷态离子与微孔箔的相互作用研究

低速高电荷态离子与纳米微孔箔相互作用的研究无论在基础研究方面还是实际应用方面都扮演着重要的角色，因此在近年来受到了广泛的关注，成为一个研究热点。 论文介绍了在兰州重离子加速器国家实验室320kV高压电子回旋共振离子源（ECRIS）上新建成的表面物理实验终端；着重叙述了在该终端上开展的高电荷态离子与绝缘体纳米微孔箔相互作用的实验工作，包括高电荷态离子穿过微孔箔后的电荷态分布、角分布以及微孔箔的导向能力；系统的研究和讨论了（1）出射离子的电荷态分布；（2）出射离子产额的角度分布，具体内容有入射倾角、入射离子的动能、电荷态以及后表面带电对角度分布的半高宽度的影响；（3）微孔箔导向能力，具体内容有表征导向能力的临界角、入射离子的动能、电荷态的变化以及后表面带电对临界角的影响；（4）总的离子产额随入射离子束流强的变化情况。 实验结果表明，微孔箔对入射的低速高电荷态离子有明显的导向作用，出射离子的角度分布为对称分布，且超过97%的出射离子保持了入射时的电荷态；入射倾角、初始动能、初始电荷态以及微孔箔后表面带电与否等对离子产额角度分布的半高宽和临界角会产生影响；总的离子产额会随入射流强的变化出现拐点。论文还利用导向效应模型对实验中出现的各种现象进行了定性的解释，并对进一步深入研究该项课题提出了初步的设想