987 resultados para heavy ion collisions
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Viscous modifications to the thermal distributions of quark-antiquarks and gluons have been studied in a quasiparticle description of the quark-gluon-plasma medium created in relativistic heavy-ion collision experiments. The model is described in terms of quasipartons that encode the hot QCD medium effects in their respective effective fugacities. Both shear and bulk viscosities have been taken in to account in the analysis, and the modifications to thermal distributions have been obtained by modifying the energy-momentum tensor in view of the nontrivial dispersion relations for the gluons and quarks. The interactions encoded in the equation of state induce significant modifications to the thermal distributions. As an implication, the dilepton production rate in the q (q) over bar annihilation process has been investigated. The equation of state is found to have a significant impact on the dilepton production rate along with the viscosities.
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Collector-type experiments have been conducted to investigate two different aspects of sputtering induced by keV ions. The first study looked for possible ejection mechanisms related to the primary charge state of the projectile. Targets of CsI and LiNbO_3 were bombarded with 48 keV Ar^(q+), and a Au target was bombarded with 60 keV Ar^(q+), for q = 4, 8, and 11. The collectors were analyzed using heavy-ion Rutherford backscattering spectroscopy to determine the differential angular sputtering yields; these and the corresponding total yields were examined for variations as a function of projectile charge state. For the Au target, no significant changes were seen, but for the insulating targets slight (~10%) enhancements were observed in the total yields as the projectile charge state was increased from 4+ to 11+.
In the second investigation, artificial ^(92)Mo/^(100)Mo targets were bombarded with 5 and 10 keV beams of Ar^+ and Xe^+ to study the isotopic fractionation of sputtered neutrals as a function of emission angle and projectile fluence. Using secondary ion mass spectroscopy to measure the isotope ratio on the collectors, material ejected into normal directions at low bombarding fluences (~ 10^(15) ions cm^(-2)) was found to be enriched in the light isotope by as much as ~70‰ compared to steady state. Similar results were found for secondary Mo ions sputtered by 14.5 keV O^-. For low-fluence 5 keV Xe^+ bombardment, the light-isotope enrichment at oblique angles was ~20‰ less than the corresponding enrichment in the normal direction. No angular dependence could be resolved for 5 keV Ar^+ projectiles at the lowest fluence. The above fractionation decreased to steady-state values after bombarding fluences of a few times 10^(16) ions cm^(-2) , with the angular dependence becoming more pronounced. The fractionation and total sputtering yield were found to be strongly correlated, indicating that the above effects may have been related to the presence of a modified target surface layer. The observed effects are consistent with other secondary ion measurements and multiple-interaction computer simulations, and are considerably larger than predicted by existing analytic theory.
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The two-pulse stimulated radiation of dense (10^9/cm^3 < ne ≤ 10^(11) /cm^3) nonuniform neon and argon afterglow plasma columns longitudinally immersed in a magnetic field is studied. The magnetic field is very homogeneous over the plasma volume (∆B/B~.01%). If the S-band microwave pulses' center frequency is such that they resonantly excite a narrow band of plasma upper hybrid oscillations close to the maximum upper hybrid frequency of the column, strong two pulse echoes are observed. This new echo process is called the upper hybrid echo. The echo spectrum, echo power and echo width were studied as a function of the pulse peak power P, pulse separation τ, relative density (ω_(po)/ω)^2, and relative cyclotron frequency (ω_c/ω). The complex but systematic variations of the echo properties as a function of the above-mentioned parameters arc found to be in qualitative agreement with those predicted by a theory of Gould and Blum based upon a simple nonuniform unidimensional cold plasma slab model. The possible effects of electron neutral and electron ion collisions not retained in the theoretical model are discussed.
The existence of a new type of cyclotron echo, different from that of Hill and Kaplan and not predicted by the Blum and Gould model is documented. It is believed to be also of a collective effect nature and can probably be described in terms of a theory retaining some hot plasma effects.
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A microelectronic parallel electron-beam lithography system using an array of field emitting microguns is currently being developed. This paper investigates the suitability of various carbon based materials for the electron source in this device, namely tetrahedrally bonded amorphous carbon (ta-C), nanoclustered carbon and carbon nanotubes. Ta-C was most easily integrated into a gated field emitter structure and various methods, such as plasma and heavy ion irradiation, were used to induce emission sites in the ta-C. However, the creation of such emission sites at desired locations appeared to be difficult/random in nature and thus the material was unsuitable for this application. In contrast, nanoclustered carbon material readily field emits with a high site density but the by-products from the deposition process create integration issues when using the material in a microelectronic gated structure. Carbon nanotubes are currently the most promising candidate for use as the emission source. We have developed a high yield and clean (amorphous carbon by-product free) PECVD process to deposit single free standing nanotubes at desired locations with exceptional uniformity in terms of nanotube height and diameter. Field emission from an array of nanotubes was also obtained. © 2001 Elsevier Science B.V.
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Ni/SiO2 interface were irradiated at room temperature with 308 MeV Xe ions to 1×1012,5×1012 Xe/cm2 and 853 MeV Pb ions to 5×1011 Pb/cm2,respectively.These samples were analyzed using Rutherford Backscattering Spectrometry(RBS) and X-ray diffraction spectroscopy(XRD),from which the intermixing and phase change were investigated.The obtained results show that both Xe-and Pb-ions could induce diffusion of Ni atoms to SiO2 substrates and result in intermixing of Ni with SiO2.Furthermore,1.0×1012 Xe/cm2 irradiat...中文摘要:在室温下用308 MeV的Xe离子和853 MeV的Pb离子辐照Ni/SiO2样品,用卢瑟福背散射和X射线衍射技术对样品进行了分析。通过分析Ni/SiO2样品中元素成分分布和结构随离子辐照剂量和电子能损的变化,探索了离子辐照在Ni/SiO2样品中引起的界面原子混合与结构相变现象。实验结果显示,Xe和Pb离子辐照均能引起明显的Ni原子向SiO2基体的扩散并导致界面附近Ni,Si和O原子的混合。实验观测到低剂量Xe离子辐照可产生NiSi2相,而高剂量Xe离子辐照则导致了Ni3Si和NiO相的形成。根据热峰模型,Ni原子的扩散和新相的形成可能由沿离子入射路径强电子激发引起的瞬间热峰过程驱动。
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Low-activation Ferritic/Martensitic steels are a kind of important structural materials candidate to the application in advanced nuclear energy systems.Possible degradation of properties and even failure in the condition of high-temperature and high helium production due to energetic neutron irradiation in a fusion reactor is a major concern with the application of this kind of materials.In the present work microstructural evolution in a 9Cr Ferritic/Martensitic steel(T92B) irradiated with 122 MeV 20Ne ions...中文摘要:低活化的铁素体/马氏体钢是先进核能装置(如聚变堆)的重要候选结构材料。在聚变堆实际工作环境下,由于高温和高氦产生率引起的材料失效是这类材料面临的一个重要问题。本项研究以兰州重离子加速器(HIRFL)提供的中能惰性气体离子束(20Ne,122 MeV)作为模拟辐照条件,借助透射电子显微镜,研究了一种低活化的9Cr铁素体/马氏体钢(T92B)组织结构的变化和辐照肿胀。实验结果表明,高温下当材料中晶格原子的撞出损伤和惰性气体原子沉积浓度超过一定限值时,材料内部形成高浓度的空洞,并且空洞肿胀率显著依赖于辐照温度和剂量;在马氏体板条界面及其它晶界处空洞趋于优先形成,并且在晶界交汇处呈加速生长。基于氦泡的形核生长与空洞肿胀的经典模型探讨了在不同辐照条件(He离子、Ne离子、Fe/He离子双束、快中子、Ni离子)下铁素体/马氏体钢中肿胀率数据的关联。
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This paper describes the technique targets and operation principle of the scanning power supply for the deep tumor therapy facility with heavy ions in Cooler-Storage-Ring of the Heavy Ion Research Facility in Lanzhou(HIRFL-CSR).To ensure the specified accuracy of the current,the hysteresis loop control strategy was adopted,and tracking error was constrained in the specified tolerance.One prototype was designed and installed.And the simulation results and test results were listed in the paper.The results sho...中文摘要:阐述了用于兰州重离子深层治癌装置的扫描电源的技术指标和工作原理,为保证该电源输出电流的精度,采用滞环控制策略,将跟踪误差限制在设计要求的误差范围内。研制了1台扫描电源样机,并给出了电路仿真和测试结果。测试结果显示各项指标均达到了设计要求,表明所选电路结构和滞环控制方案是切实可行的。
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Purpose The aim of this study is to evaluate the eVect of carbon-beam irradiation on adenovirus-mediated p53 transfer in human cervix adenocarcinoma.Materials and methods The HeLa cells pre-exposed to carbon-beam or -ray, were infected with replication-deficient adenovirus recombinant vectors, containing human wild-type p53 (AdCMV-p53) and green Xuorescent protein (GFP) (AdCMV–GFP), respectively. The GFP transfer and p53 expression were detected by Xow cytometric analysis.Results The GFP transfer frequency in C-beam with AdCMV-GFP groups was 38–50% more than that inγ-ray with AdCMV–GFP groups. The percentage of p53 positive cells in the C-beam with AdCMV–p53 groups was 34–55.6% more than that in γ-ray with AdCMV-p53 groups (p < 0.05), suggesting that subclinical-dose C-beam irradiation could signiWcantly promote exogenous p53 transfer and p53 expression, and extend the duration of p53 expression in the HeLa cells. The expression of p21 increased with p53 expression in HeLa cells. The survival fractions for the 0.5–1.0 Gy C-beam with AdCMV-p53 groups were 38–43% less than those for the isodose γ-ray with AdCMV-p53 groups, and 31–40% less than those for the C-beam only groups (p <0.05).Conclusions The subclinical-dose C-beam irradiation could signiWcantly promote the transfer and expression of exogenous p53, extend the duration of p53 expression, and enhance the suppression of p53 on cervix adenocarcinoma cells.
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Basic algorithms of biological effective dose optimization and dose distribution on CT image for the heavy ion therapy project at the Institute of Modern Physics(IMP),Chinese Academy of Sciences(CAS) are reported in this paper.Firstly,biological effective dose optimization is conducted in water.According to the relationship between CT number and water equivalent path length,an integral algorithm is used to calculate the average dose within a pixel and then the dose distribution in tissue is derived.Secondly...中文文摘:针对深部肿瘤重离子治疗临床试验的需求,首先在水介质中进行生物有效剂量的优化计算,然后根据CT图像中像素CT值与水等效长度转换系数之间的关系,结合水中的深度剂量分布曲线对每个像素进行积分得到CT图像上的生物有效剂量分布。同时介绍了基于被动式束流配送系统适形照射时的剂量确定方式,并提出二维适形放疗也应使用分层照射方式以适应治疗时的不同要求。这些方法适合目前及今后在IMP进行的重离子治癌临床试验研究中治疗计划系统的需要。
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HIRFL-CSR, a new heavy ion cooler-storage-ring system at IMP, had been in commissioning since the beginning of 2006. In the two years of 2006 and 2007 the CSR commissioning was finished, including the stripping injection (STI), electron-cooling with hollow electron beam, C-beam stacking with the combination of STI and e-cooling, the wide energy-range synchrotron ramping from 7 MeV/u to 1000 MeV/u by changing the RF harmonic-number at mid-energy, the multiple multi-turn injection (MMI), the beam accumulation with MMI and e-cooling for heavy-ion beams of Ar, Kr and Xe, the fast extraction from CSRm and single-turn injection to CSRe, beam stacking in CSRe and the RIBs mass-spectrometer test with the isochronous mode in CSRe by using the time-of-flight method.
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A new generation electron cooler has started operation in the heavy ion synchrotron CSRm which is used to increase the intensity of heavy ions. Transverse cooling of the ion beam after horizontal multi-turn injection allows beam accumulation at the injection energy. After optimization of the accumulation process an intensity increase in a synchrotron pulse by more than one order of magnitude has been achieved. In given accumulation time interval of 10 seconds, 108particles have been accumulated and accelerated to the final energy. The momentum spread after accumulation and acceleration in the 10−4 range has been demonstrated in six species of ion beams. Primary measurements of accumulation process varying with electron energy,electron beam current, electron beam profile, expansion factor and injection interval have been performed.The lifetimes of ion beams in the presence of electron beams were roughly measured with the help of DCCT signal.
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In commissioning the HIRFL-CSR (Cooler Storage Ring of Heavy Ion Research Facility in Lanzhou),with the spectrum analyzer monitoring the beams on-line, we measured many parameters of the beam status for improving quality of the heavy ion beams. In this paper, the sudden change of the beam center frequency is analyzed.A theoretical analysis is done mainly on instabilities of the electron voltage and the neutralization factor. Simulations were made for the problem. According to the simulation result, we can conclude that it is the instability of neutralization factor that caused the problem. 中文摘要:HIRFL-CSR调试过程中,利用频谱分析仪实时监测束流,根据其上测的数据进行相关参数调整,改善束流的品质。本文对分析仪上观测到的现象一束流的中心频率发生突变进行了研究,主要就电子束的高压不稳定性和中性化因子的突变做了理论分析,并进行了相关的模拟计算 ,根据模拟结果初步断定该现象的出现由电子束的中性化因子导致。
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In order to investigate the effect of carbon ion irradiation on apoptosis and Bax/Bcl-2 expression inhuman tongue carcinoma cells, exponentially growing human tongue carcinoma cells (Tb) cultured in vitro were irradiated with 0, 0.5, 1.0, 2.0 or 4.0 Gy of 12C6+ ions respectively. Survival rate of irradiated cells at various doses were measured by MTT assay. The nucleus changes of apoptosis and necrosis of cells stained by Hochest/PI were observed through fluorescence microscope. The cell cycle changes were detected by flow cytometry (FCM). The expressions of Bax and Bcl-2 were detected by Western blot analysis. The results show that the viability of Tb cells decreases gradually with increment of irradiation doses of carbon ions. The proportions of apoptosis cells in the irradiated groups are significantly higher than those in the control group. There is a positive correlation between irradiation doses and retardation strength in G2 /M phase at 24 h after irradiation (P<0.05). And the expressions of Bax and bcl-2 are significantly up-regulated and down-regulated respectively by 12C6+ ion irradiation. It can be concluded from above that cell apoptosis induced by heavy ion with high-LET may be mediated through the Bax/Bcl-2 expression pathway. 探讨重离子辐照对人舌鳞癌Tb细胞的凋亡及Bax/Bcl-2蛋白表达的影响。采用0、0.5、1.0、2.0、4.0 Gy重离子束辐照人舌鳞癌 Tb 细胞,应用 MTT 法检测细胞存活,流式细胞技术检测细胞周期变化,Hoechst33258/PI 复染法观察 Tb 细胞凋亡形态,并采用 Western-blot 法检测 Bax/Bcl-2 蛋白表达情况。结果发现,Tb细胞经12C6+离子束辐照后存活率显著下降,呈剂量依赖性的生长抑制;Tb细胞呈现蓝色荧光浓集成团的凋亡形态,且凋亡比例随辐照剂量增加;G2/M 期细胞百分数随照射剂量增加而增加(P<0.05) 。Western-blot结果显示 Bax 蛋白表达水平随辐照剂量逐渐上升,但在 4 Gy 组其表达不再增高,Bcl-2 蛋白在 1.0、2.0、4.0 Gy组随剂量增大呈下降趋势。以上结果提示重离子束辐照对 Tb 细胞有抑制作用,Bax/Bcl-2 蛋白表达是重离子治癌的机制之一。
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This paper introduced a real-time vacuum monitor system based on multilayer Web architecture for HIRFL-CSR(Heavy Ion Research Facility of Lanzhou & Cooler Storage Ring) project in Lanzhou.It combined with COM/DCOM to develop the application layer,and developed the web layer with ActiveX and Ajax technology.It provided a facility and efficiency method for real-time control.The application shows that this system runs stably and accurately.中文文摘:简要介绍了国家"九五"重大科学工程——兰州重离子加速器冷却储存环(HIRFL-CSR)真空监控系统的总体结构,分析了在Web构架下,基于分布式内存数据库的多层真空监控系统的实现方法。采用分布式内存数据库,解决了基于Web构架的分布式实时应用环境下对系统和网络资源的消耗问题。在软件控制方面采用了统一调度,既简化了软件实现过程,又提高了系统的安全性、高效性和易维护性。该系统已成功运行。