HIRFL-CSR ETF多层CsI(Tl)望远镜探测器能量刻度方法

在兰州重离子加速器冷却储存环（HIRFL-CSR）的外靶终端（ETF）,设计建造了一套多层CsI（Tl）望远镜探测器,用于对轻质量带电粒子的鉴别。这套探测器由7层CsI（Tl）晶体组成,每一层晶体光输出信号由4个光电倍增管分别在晶体4角读出。由于CsI（Tl）晶体对于重离子的响应是非线性的,且与入射离子的种类有关,这些因素使得对这台探测器的能量刻度需要做专门的研究。利用RIBLL2提供的能量在200 s~300 MeV/u的次级束流对探测器进行了测试,并针对第一片CsI（Tl）晶体的光输出以及所有CsI（Tl）晶体光输出的和的刻度方法分别进行了探索。在此能区下,第一片CsI（Tl）晶体猝灭现象可以近似忽略,即光输出与能量沉积近似呈线性。对于所有晶体光输出的和,利用一个经验公式对其进行刻度,利用这种刻度方法计算得到的光输出的值与实验测量值之间的差别小于5%。A multi-layer CsI(Tl) telescope has been designed and constructed at External Target in Facility (ETF) terminal of the Cooling Storage Ring of Heavy Ion Research Facility in Lanzhou(HIRFL-CSR), and is used for identifying light charged particles. The detector consists of seven layers of CsI(Tl) crystals, and the signals of each crystal are read out by four photomultipliers at the corners. Since the response of the CsI(Tl) crystal to the heavy ions is non-linear and also depends on the species of the incident ions, the energy calibration method of the telescope must be carefully studied. With the help of the secondary beams selected by RIBLL2 in the energy ranges from 200 to 300 MeV/u, the telescope has been tested and the energy calibration method for the first-layer crystal together with the whole telescope has been investigated. In this energy region, the quench effect in the first-layer crystal can be neglected and a linear expression can be used to represent the relation between the light output and the energy deposition in the crystal. To the total light output of the telescope, an empirical formula is used for the energy calibration. The difference between the calculated results and the experiment data is globally less than 5%.     

CsI（Tl）+Si-APD探测器的性能测试

介绍了Si-APD的工作原理并对Si-APD中的暗电流进行了理论分析。基于RIBLL上产生的放射性核束流,使用CsI（Tl）+Si-APD探测器对中能重离子进行了能量测试。测试结果显示,CsI（Tl）+Si-APD探测器测量20 MeV/u的重离子时,可得到3%的能量分辨;同时还发现Si-APD中的暗电流大小以及入射粒子的能量大小都会对探测器的能量分辨产生影响。In this paper, the working principle of Si-APD was introduced and the dark current of Si-APD was analyzed theoretically. The intermediate energy heavy ions, which are produced on the RIBLL(Radioactive Ion Beam Line in Lanzhou), were measured with CsI(Tl)+Si-APD detector. The energy resolution of CsI(Tl)+Si-APD detector is about 3% for heavy ions with energy around 20 MeV/u. It is also found that the energy resolution of detector can be in uenced by the dark current of Si-APD and the energy of incident particles.     

Property measurement of the CsI(Tl) crystal prepared at IMP

Large-sized CsI(Tl) single crystals, ～φ100mm×350mm, have been grown successfully, and this CsI(Tl) coupled with PD has been successfully utilized at RIBLL (the Radioactive Ion Beam Line in Lanzhou) to measure the energy of heavy ions as a stopping detector. The performances of CsI(Tl) detector coupled with PD and APD have been tested and compared, including the temperature dependence of scintillating light yield.     

中能重离子碰撞中横向流电荷依赖的形状以及实验条件对横向流的影响(英文)

从35 MeV/nucleon 40Ca+40Ca反应实验数据中提取了碎片Z从1到9的横向流,发现探测器阈值、探测系统的角分辨等实验条件对横向流电荷依赖的形状有显著的影响。在考虑实验条件并采用软的核物质状态方程（K=200 MeV）之后,CoMD模型计算结果很好地重现了实验中横向流电荷依赖的形状。这表明如果要更加精确地提取实验中的横向流,必须使用阈值更低、角分辨更好的探测系统。此外,结合Kohley等[Phys Rev C,2012,85:064605]从实验中提取的横向流,讨论了横向流电荷依赖的形状存在异同的原因。1 ≤ Z ≤ 6的横向流电荷依赖呈肩峰形状可能是实验条的影响引起的,而我们的实验中Z ≥ 6的横向流的减小可能是由于动量守恒对集体运动的抑制。The transverse flow in the reaction of 40Ca+40Ca at 35 MeV/nucleon has been determined for emitted isotopes with Z=1 to 9. A significant modification of the Z-dependent flow pattern caused by the experimental filters, the detector thresholds and the angular resolutions (△?) of the detector array, is observed. With the application of the appropriate experimental filters, the general trend of the experimental Z-dependent flow is well reproduced by the Constrained Molecular Dynamics (CoMD) simulation, employing an effective interaction corresponding to a soft EOS (K=200 MeV). This fact suggests that to determine the flow values more precisely, a detection system with lower energy threshold and better angular resolution is urgently required. Additionally, together with the parallel work of Z. Kohley et al.[Phys Rev C, 2012, 85:064605], the pattern of the experimental Z dependence of transverse flow is also discussed. The shoulder patterns of Z-dependent flow for 1 ≤ Z ≤ 6 can be attributed by the experimental filters, while the reduction of flow for Z ≥ 6 in our experiment can be caused by the suppression of collective motion under the momentum conservation.     

Design of the IMP microbeam irradiation system for 100 MeV/u heavy ions

A state-of-the-art high energy heavy ion microbeam irradiation system is constructed at the Institute of Modern Physics of the Chinese Academy of Sciences. This microbeam system operates in both full current intensity mode and single ion mode. It delivers a predefined number of ions to pre-selected targets for research in biology and material science. The characteristic of this microbeam system is high energy and vertical irradiation. A quadrupole focusing system, in combination with a series of slits, has been designed to optimize the spatial resolution. A symmetrically achromatic system leads the beam downwards and serves simultaneously as an energy analyzer. A high gradient quadrupole triplet finally focuses a C^6＋ ion beam to 1 μm in the vacuum chamber within the energy range from 10 MeV/u to 100 MeV/u. In this paper, the IMP microbeam system is described in detail. A systematic investigation of the ion beam optics of this microbeam system is presented together with the associated aberrations. Comparison is made between the IMP microbeam system and the other existing systems to further discuss the performance of this microbeam. Then the optimized initial beam parameters are given for high resolution and high hitting efficiency. At last, the experiment platform is briefly introduced.     

Neutron dose measurement in carbon ion radiation therapy at HIRFL （IMP）

For radiation protection purposes, the neutron dose in carbon ion radiation therapy at the HIRFL （Heavy Ion Research Facility in Lanzhou） was investigated. The neutron dose from primary ^12C ions with a specific energy of 100 MeV/u delivered from SSC was roughly measured with a standard Anderson-Broun rem-meter using a polyethylene target at various distances. The result shows that a maximum neutron dose contribution of 19 mSv in a typically surface tumor treatment was obtained, which is less than 1% of the planed heavy ion dose and is in reasonable agreement with other reports. Also the T-ray dose was measured in this experiment using a thermo luminescent detector.     

Conceptional design of a heavy ion linac injector for HIRFL-CSRm

A room temperature heavy ion linac has been proposed as a new injector of the main Cooler Storage Ring(CSRm) at the Heavy Ion Research Facility in Lanzhou(HIRFL), which is expected to improve the performance of HIRFL. The linac injector can supply heavy ions with a maximum mass to charge ratio of 7 and an injection kinetic energy of 7.272 MeV/u for CSRm; the pulsed beam intensity is 3 emA with the duty factor of 3%. Compared with the present cyclotron injector, the Sector Focusing Cyclotron(SFC), the beam current from linac can be improved by 10–100 times. As the pre-accelerator of the linac, the 108.48 MHz 4-rod Radio Frequency Quadrupole(RFQ) accelerates the ion beam from 4 keV/u to 300 keV/u, which achieves the transmission efficiency of 95.3% with a 3.07 m long vane.The phase advance has been taken into account in the analysis of the error tolerance, and parametric resonances have been carefully avoided by adjusting the structure parameters. Kombinierte Null Grad Struktur Interdigital H-mode Drift Tube Linacs(KONUS IH-DTLs), which follow the RFQ, accelerate ions up to the energy of 7.272 MeV/u for CSRm. The resonance frequency is 108.48 MHz for the first two cavities and 216.96 MHz for the last 5 Drift Tube Linacs(DTLs). The maximum accelerating gradient can reach 4.95 MV/m in a DTL section with the length of17.066 m, and the total pulsed RF power is 2.8 MW. A new strategy, for the determination of resonance frequency,RFQ vane voltage and DTL effective accelerating voltage, is described in detail. The beam dynamics design of the linac will be presented in this paper.     

A new compact structure for a high intensity low-energy heavy-ion accelerator

A new compact accelerating structure named Hybrid RFQ is proposed to accelerate a high-intensity low-energy heavy ion beam in HISCL （High Intensive heavy ion SuperConducting Linear accelerator）, which is an injector of HIAF （Heavy Ion Advanced Research Facility）. It is combined by an alternative series of acceleration gaps and RFQ sections. The proposed structure has a high accelerating ability compared with a conventional RFQ and is more compact than traditional DTLs. A Hybrid RFQ is designed to accelerate 238U34＋ from 0.38 MeV/u to 1.33 MeV/u. The operation frequency is described to be 81.25 MHz at CW （continuous wave） mode. The design beam current is 1.0 mA. The results of beam dynamics and RF simulation of the Hybrid RFQ show that the structure has a good performance at the energy range for ion acceleration. The emittance growth is less than 5% in both directions and the RF power is less than 150 kW. In this paper, the results of beam dynamics and RF simulation of the Hybrid RFQ are presented.     

面向空间高能重离子与辐射屏蔽材料的反应截面地基研究

空间辐射尤其是高能重离子辐射可造成生物机体的严重损伤, 所以对高能重离子进行恰当的辐射屏蔽, 成为实现载人航天的关键性因素之一。 研究表明, 由于高能重离子与不同屏蔽材料发生相互作用, 所产生的核碎片等次级粒子, 直接影响空间辐射屏蔽材料的屏蔽性能研究和屏蔽结构设计。 介绍了太空辐射的分类与组成, 综述了国际地基辐射屏蔽材料与实验现状。 根据文献中的地基实验数据, 重点描述了被动式屏蔽方法: 以相近能量多种重离子, 不同能量的56Fe和28Si重离子分别与C, H, Al和Cu材料相互作用的总反应截面和碎片产生截面, 并结合510 MeV/u 56Fe与不同厚度CH2相互作用产生的碎片通量分布、 碎片平均LET分布和不同厚度CH2的单位入射离子剂量减少量等方面, 系统讨论分析了C, H, Al, Cu和CH2等常用空间辐射屏蔽材料的屏蔽性能。 Cosmic radiation, particularly the high energy heavy ion radiation, may cause serious injury on living organism. Therefore, it is one of critical restriction factor in Manned Spaceflight. Studies show that high energy heavy ions interacting with the shielding materials can produce numerous kinds of fragments and secondaries. These particles have a direct impact on evaluation of shielding properties of different shielding materials, the optimal shielding structure design and low dose evaluation after shielding materials. From perspectives of divisions of cosmic rays and passive shielding methods, this paper introduces the ground based research of shielding materials. The passive shielding method was discussed, based on the experimental data of the total cross sections and fragment（production） cross sections of the aspects of different heavy ions with approximately same energy and 56Fe, 28Si heavy ions with different energies on H, C, CH2, Al and Cu radiation shielding materials. In addition, the fragment fluency distribution, the average LET distribution and the dose reduction per particle of 510 MeV/u 56Fe in different depth of CH2 material were also discussed.     

Fast light of CsI（Na） crystals

The responses of different common alkali halide crystals to alpha-rays and gamma-rays are tested in this research. It is found that only CsI(Na) crystals have significantly different waveforms between alpha and gamma scintillations, while others do not exhibit this phenomena. The rise time of the fast light is about 5 ns and the decay time is 17±12 ns. It is suggested that the fast light of CsI(Na) crystals arises from the recombination of free electrons with self-trapped holes of the host crystal CsI. Self-absorption limits the emission of fast light of CsI(Tl) and NaI(Tl) crystals.     

兰州重离子加速器冷却储存环

 兰州重离子加速器冷却储存环HIRFL-CSR,是一个多用途、多功能的双冷却储存环同步加速器系统,由主环CSRm和实验环CSRe构成,并以兰州重离子级联回旋加速器HIRFL作注入器。CSR利用高频变谐波的方法,将重离子束的能量从7～25 MeV/u同步加速到２00～1 000 MeV/u,同时利用重离子储存环中空心电子束冷却技术将束流品质提高１个数量级,并通过储存环的快引出及慢引出,提供多种类的重离子束以及放射性次级束(RIBs),以开展范围更广精度更高的物理实验。该装置于2007年投入运行,已取得了重要的运行结果,如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的产生收集与ToF高分辨质量测量以及高能重离子束的变能慢引出等。     

BaF2 Used for Particle Identification in Intermediate Energy Heavy Ion Raactions

A detector telescope consisting of a BaF₂ crystal and Si detectors is used to measure forwardly emitted products in ¹²C(46.7MeV/u)induced heavy ion reactions,both ΔE-E method and fast-slow correlation method are adopted in the particle identification.The response of BaF₂ to various incident ions has been studied.     

Neutron dose measurement in carbon ion radiation therapy at HIRFL (IMP)

For radiation protection purposes, the neutron dose in carbon ion radiation therapy at the HIRFL (Heavy Ion Research Facility in Lanzhou) was investigated. The neutron dose from primary 12C ions with a specific energy of 100 MeV/u delivered from SSC was roughly measured with a standard Anderson-Broun rem-meter using a polyethylene target at various distances. The result shows that a maximum neutron dose contribution of 19 mSv in a typically surface tumor treatment was obtained, which is less than 1% of the planed heavy ion dose and is in reasonable agreement with other reports. Also the γ-ray dose was measured in this experiment using a thermo luminescent detector.     

IMP-8 observations of the spectra, composition, and variability of solar heavy ions at high energies relevant to manned space missions.

In more than 25 years of almost continuous observations, the University of Chicago's Cosmic Ray Telescope (CRT) on IMP-8 has amassed a unique database on high-energy solar heavy ions of potential relevance to manned spaceflight. In the very largest particle events, IMP-8/CRT has even observed solar Fe ions above the Galactic cosmic ray background up to approximately 800 MeV/nucleon, an energy sufficiently high to penetrate nearly 25 g/cm2 of shielding. IMP-8/CRT observations show that high-energy heavy-ion spectra are often surprisingly hard power laws, without the exponential roll-offs suggested by stochastic acceleration fits to lower energy measurements alone. Also, in many solar particle events the Fe/O ratio grows with increasing energy, contrary to the notion that ions with higher mass-to-charge ratios should be less abundant at higher energies. Previous studies of radiation hazards for manned spaceflight have often assumed heavy-ion composition and steeply-falling energy spectra inconsistent with these observations. Conclusions based on such studies should therefore be re-assessed. The significant event-to-event variability observed in the high-energy solar heavy ions also has important implications for strategies in building probabilistic models of solar particle radiation hazards.     

Radiation Protection of CSR

The construction of CSR (cooling storage ring) which includes a main ring (CSRm) and an experimental ring (CSRe) will be finished at the end of 2005. Heavy ions of carbon to uranium will be accelerated up to 900MeV/u and 400MeV/u at intensity of 10⁸ pps. The HIRFL (heavy ion research facility in Lanzhou) will be used as the injector. For the shielding design of CSR, the secondary neutrons due to the ion beam loss, their spectra and angular distributions were estimated based on the experimental results. The dose equivalent outside the shielding surface and in the surrounding environment and the neutron skyshine dose equivalent were also estimated in this study. The experimental result, neutron yield, spectrum and angular distribution for 400MeV/u ¹²C+Cu reaction were used for estimating the source term of shielding design. It is found that the most important environmental radiation impact component of CSR is the skyshine neutrons.     

CSR的辐射防护

CSR(cooling storage ring)按计划将于2005年底建成调束,届时从¹²C到²³⁸U的重离子将可以分别被加速到900和400MeV的能量. HIRFL(兰州重离子加速器Heavy Ion Research Facility in Lanzhou)将 用作CSR的注入器. 为了CSR的屏蔽设计,本文利用现有的实验数据计算了由于束流损失产生的中子及其能谱、角分布,同时也估算了屏蔽体外表面的中子剂量、环境中子剂量及天空返照中子剂量. 在源项计算中使用了400MeV/u ¹²C+Cu反应的中子产额、能谱、角分布的实验数据. 计算表明, CSR对环境剂量影响最大的是天空返照中子.     

用于裂变碎片质量测量的MCP和Au-Si SBD飞行时间探测系统

为了能很好地鉴别碎片质量,建立一个好的飞行时间测量方法是十分必要的。阐述了建立用于裂变碎片质量测量的微通道板（MCP）和金硅面垒探测器（SBD）飞行时间探测系统。对于80 μg/cm2厚的碳膜,241Am的α粒子的探测效率约为39%,252Cf（sf）裂变碎片的探测效率约为98%。在动能为78 MeV条件下,对252Cf（sf）重裂变碎片（138~148 u）得到的时间分辨为（224:1±6:1）ps;在动能为102 MeV条件下,对252Cf（sf）轻裂变碎片（101~111 u）,得到的时间分辨为（154:5±5:8）ps。In order to separate the mass number of fragments in the fission reactions, it is essential to develop a good time-of-flight (TOF) method. The purpose of this article is to set up a TOF detector system including a microchannel plate (MCP) and a Au-Si surface-barrier detector (SBD). The TOF system shows a detection efficiency of 39% for α-particles released from 241Am and 98% for fragments in the spontaneous fission of 252Cf. The experimental results show that the time resolutions of (224:1±6:1) ps for the heavy fragments (Ek=78 MeV, AH=138~148 u) and (154:5±5:8) ps for the light fragments (Ek=102 MeV, AL=101~111 u) can be obtained.     

一种用于RIBLL2的纵向场多次取样型电离室

为兰州第二条放射性束流线（RIBLL2）研制了一台用于ΔE测量的纵向场多次取样型电离室。 利用3组分α源（239Pu为3.435 MeV, 241Am为3.913 MeV, 244Cm为4.356 MeV）对取样单元进行了测试, 确定了电离室的最佳工作电压为－500 V, 沉积能量为3.435 MeV时, 取样单元的能量分辨为271.4 keV(FWHM)。 利用Geant4对此电离室的整体性能进行了模拟, 表明可以对Z≥4的离子实现较好的粒子鉴别。 A longitudinal field MUltiple Sampling Ionization Chamber (MUSIC), which makes multiple measurements of energy loss for very high energy heavy ions at RIBLL2, has been constructed and tested with 3 constituent α source （239Pu: 3.435 MeV, 241Am: 3.913 MeV, 244Cm: 4.356 MeV）. The voltage plateau curve has been plotted and －500 V is determined as a proper work voltage. The energy resolution is 271.4 keV FWHM for the sampling unit when 3.435 MeV energy deposited. A Geant4 Monte Carlo simulation is made and it indicates the detector can provide unique particle identification for ions Z≥4.