Charged and strange hadron elliptic flow in Cu plus Cu collisions at root s(NN)=62.4 and 200 GeV

We present the results of an elliptic flow, v(2), analysis of Cu + Cu collisions recorded with the solenoidal tracker detector (STAR) at the BNL Relativistic Heavy Ion Collider at root s(NN) = 62.4 and 200 GeV. Elliptic flow as a function of transverse momentum, v(2)(p(T)), is reported for different collision centralities for charged hadrons h(+/-) and strangeness-ontaining hadrons K-S(0), Lambda, Xi, and phi in the midrapidity region vertical bar eta vertical bar < 1.0. Significant reduction in systematic uncertainty of the measurement due to nonflow effects has been achieved by correlating particles at midrapidity, vertical bar eta vertical bar < 1.0, with those at forward rapidity, 2.5 < vertical bar eta vertical bar < 4.0. We also present azimuthal correlations in p + p collisions at root s = 200 GeV to help in estimating nonflow effects. To study the system-size dependence of elliptic flow, we present a detailed comparison with previously published results from Au + Au collisions at root s(NN) = 200 GeV. We observe that v(2)(p(T)) of strange hadrons has similar scaling properties as were first observed in Au + Au collisions, that is, (i) at low transverse momenta, p(T) < 2 GeV/c, v(2) scales with transverse kinetic energy, m(T) - m, and (ii) at intermediate p(T), 2 < p(T) < 4 GeV/c, it scales with the number of constituent quarks, n(q.) We have found that ideal hydrodynamic calculations fail to reproduce the centrality dependence of v(2)(p(T)) for K-S(0) and Lambda. Eccentricity scaled v(2) values, v(2)/epsilon, are larger in more central collisions, suggesting stronger collective flow develops in more central collisions. The comparison with Au + Au collisions, which go further in density, shows that v(2)/epsilon depends on the system size, that is, the number of participants N-part. This indicates that the ideal hydrodynamic limit is not reached in Cu + Cu collisions, presumably because the assumption of thermalization is not attained.

Observation of pi(+)pi(-)pi(+)pi(-) photoproduction in ultraperipheral heavy-ion collisions at root s(NN)=200 GeV at the STAR detector

We present a measurement of pi(+)pi(-)pi(+)pi(-) photonuclear production in ultraperipheral Au-Au collisions at root s(NN) = 200 GeV from the STAR experiment. The pi(+)pi(-)pi(+)pi(-) final states are observed at low transverse momentum and are accompanied by mutual nuclear excitation of the beam particles. The strong enhancement of the production cross section at low transverse momentum is consistent with coherent photoproduction. The pi(+)pi(-)pi(+)pi(-) invariant mass spectrum of the coherent events exhibits a broad peak around 1540 +/- 40 MeV/c(2) with a width of 570 +/- 60 MeV/c(2), in agreement with the photoproduction data for the rho(0)(1700). We do not observe a corresponding peak in the pi(+)pi(-) final state and measure an upper limit for the ratio of the branching fractions of the rho(0)(1700) to pi(+)pi(-) and pi(+)pi(-)pi(+)pi(-) of 2.5% at 90% confidence level. The ratio of rho(0)(1700) and rho(0)(770) coherent production cross sections is measured to be 13.4 +/- 0.8(stat.) +/- 4.4(syst.)%.

Identified particle production, azimuthal anisotropy, and interferometry measurements in Au plus Au collisions at root s(NN)=9.2 GeV

We present the first measurements of identified hadron production, azimuthal anisotropy, and pion interferometry from Au + Au collisions below the nominal injection energy at the BNL Relativistic Heavy-Ion Collider (RHIC) facility. The data were collected using the large acceptance solenoidal tracker at RHIC (STAR) detector at root s(NN) = 9.2 GeV from a test run of the collider in the year 2008. Midrapidity results on multiplicity density dN/dy in rapidity y, average transverse momentum < p(T)>, particle ratios, elliptic flow, and Hanbury-Brown-Twiss (HBT) radii are consistent with the corresponding results at similar root s(NN) from fixed-target experiments. Directed flow measurements are presented for both midrapidity and forward-rapidity regions. Furthermore the collision centrality dependence of identified particle dN/dy, < p(T)>, and particle ratios are discussed. These results also demonstrate that the capabilities of the STAR detector, although optimized for root s(NN) = 200 GeV, are suitable for the proposed QCD critical-point search and exploration of the QCD phase diagram at RHIC.

Observation of an Antimatter Hypernucleus

Nuclear collisions recreate conditions in the universe microseconds after the Big Bang. Only a very small fraction of the emitted fragments are light nuclei, but these states are of fundamental interest. We report the observation of antihypertritons-comprising an antiproton, an antineutron, and an antilambda hyperon-produced by colliding gold nuclei at high energy. Our analysis yields 70 +/- 17 antihypertritons (3/Lambda(H) over bar) and 157 +/- 30 hypertritons (H-3(Lambda)). The measured yields of H-3(Lambda) (3/Lambda(H) over bar) and He-3 ((3)(He) over bar) are similar, suggesting an equilibrium in coordinate and momentum space populations of up, down, and strange quarks and antiquarks, unlike the pattern observed at lower collision energies. The production and properties of antinuclei, and of nuclei containing strange quarks, have implications spanning nuclear and particle physics, astrophysics, and cosmology.

Longitudinal scaling property of the charge balance function in Au plus Au collisions at root s(NN)=200 GeV

We present measurements of the charge balance function, from the charged particles, for diverse pseudorapidity and transverse momentum ranges in Au + Au collisions at root S-NN = 200 GeV using the STAR detector at RHIC. We observe that the balance function is boost-invariant within the pseudorapidity coverage vertical bar-1.3, 1.3 vertical bar. The balance function properly scaled by the width of the observed pseudorapidity window does not depend on the position or size of the pseudorapidity window. This scaling property also holds for particles in different transverse momentum ranges. In addition, we find that the width of the balance function decreases monotonically with increasing transverse momentum for all centrality classes. (c) 2010 Elsevier B.V. All rights reserved.

Enhanced photoluminescence of Ar+ implanted sapphire before and after annealing

In this paper, we studied the changes in the photoluminescence spectra of the Ar+ ion implanted monocrystalline sapphire annealed at different atmospheres and different temperatures. Single crystals of sapphire (Al2O3) with the (1 0 (1) over bar 0) (m-samples) orientation were implanted at 623 K with 110 keV Ar+ ions to a fluence of 9.5 x 10(16) ions/cm(2). Photoluminescence measurement of the as-implanted sample shows a new emission band at 506 nm, which is attributed to the production of interstitial Al atoms. The intensity of emission band at 506 nm first increased then decreased with increase in annealing temperature. For the same annealing temperature, the intensity of PL peak at 506 nm of the sample annealed in air was higher than the sample annealed in vacuum. The experimental results show that the intensity of the PL peak at 506 nm of Ar-implanted sapphire can be enhanced by subsequent annealing with an enhancement of nearly 20 times. The influence of thermal annealing of the Ar-implanted samples on the new 506 nm emission band was discussed. (C) 2009 Elsevier B.V. All rights reserved.

Enhanced nucleation of Ag nanoparticles by vacancy-type defects in Ar-ions implanted spinel

Vacancy-type defects are introduced into magnesium aluminate spine] (MgAl2O4 (1 1 0)) by Ar-ions implantation, and then Ag-ions are implanted into the depth rich in vacancy-type defects. The ultraviolet-visible spectrometry (UV-VIS) and positron annihilation spectroscopy (PAS) are used to study the influence of vacancy-type defects on nucleation of Ag nanoparticles. After introduction of vacancy-type defects the pronounced increase of surface plasmon resonance (SPR) absorbance intensity indicates that defects enhance the nucleation of Ag nanoparticles. The PAS results reveal that vacancy-type defects provide pre-nucleating centers for Ag nanoparticles nucleation and growth. (C) 2010 Elsevier B.V. All rights reserved.

Center of mass energy and system-size dependence of photon production at forward rapidity at RHIC

We present the multiplicity and pseudorapidity distributions of photons produced in Au + Au and Cu + Cu collisions at root(NN)-N-s = 62.4 and 200 GeV. The photons are measured in the region -3.7 < eta < -2.3 using the photon Multiplicity detector in the STAR experiment at RHIC. The number of photons produced per average number of participating nucleon pairs increases with the beam energy and is independent of (lie collision centrality. For collisions with similar average numbers of participating nucleons the photon multiplicities are observed to be similar for An + Au and Cu + Cu collisions at a given beam energy. The ratios of the number of charged particles to photons in the measured pseudorapidity range are found to be 1.4 +/- 0.1 and 1.2 +/- 0.1 for root(NN)-N-s = 62.4 and 200 GeV, respectively. The energy dependence of this ratio could reflect varying contributions from baryons to charged particles, while mesons are the dominant contributors to photon production in the given kinematic region. The photon pseudorapidity distributions normalized by average number of participating nucleon pairs, when plotted as a function of eta-Y-beam, are found to follow a longitudinal scaling independent of centrality and colliding ion species at both beam energies. (C) 2009 Elsevier B.V. All rights reserved.

PROJECTILE FRAGMENTATION OF Ar-36,Ar-40 INDUCED REACTIONS

Fragment yields for Z >= 5 from projectile fragmentation using primary beams of Ar-36,Ar-40 at 50 MeV/nucleon on Ni-64 target have been measured in RIBLL fragment separator. We compare the fragment cross sections with the predictions of the empirical EPAX parametrization of fragmentation cross-sections and Statistical Abration-Ablation model (SAA) by considering the RIBLL separator transmission rate. Isotope yield ratios between these two reactions were calculated and isoscaling parameters alpha and beta are extracted, their dependences on fragment atomic number Z and neutron number N were presented.

用RIMS研究低能He2+与Ar碰撞的多电子过程

用反冲离子动量谱仪研究了低能He2+与Ar碰撞的多电子交换过程。该技术的独特优势是对反冲离子末态动量的完全测量。实验上鉴别了单电子俘获SC，双电子俘获DC和转移电离TI各子过程，并得到了末态量子态布居信息，首次测量了该体系各反应道的角微分截面及直接与碰撞参数相关的信息。实验发现电子主要俘获到入射离子基态或单激发态，反冲离子处于单激发态或多激发态，并有较大几率形成空心离子。研究表明电荷交换过程中存在较强的电子-电子关联作用。角分布随反冲离子电荷态增加而变宽，并向大角度方向移动，表明碰撞参数减小，相互作用加剧。SC和DC与MCBM理论角微分截面符合很好，说明在大碰撞参数时经典近似有一定合理性。不同碰撞参数范围内反冲纵向动量分布表明，SC在碰撞参数7.2a.u.≥b≥3.6a.u.时发生机率最大，随碰撞参数减小，靶离子有不断向更高激发态过渡的趋势

聚碳酸酯膜的高能Ar离子辐照效应研究

本文简要介绍了PC材料的基本属性、用途和聚合物辐照效应的发展现状，以及荷能离子与固体相互作用的基本理论。重点描述了在兰州重离子加速器上完成的1.4GeV Ar离子辐照PC膜实验和辐照样品的付里叶转换红外谱（FT-IR）、紫外、可见光谱（UV、VIS）、X-射线光电子谱（XPS）和电子自旋共振谱（ESR）分析。分析结果表明：高能Ar离子在PC膜中引起的的主要辐照效应是键的断裂和材料的降解，重要降解发生在能量沉积密度大于8.0 * 10~(22)eV/cm~3或者电子能损大于1.4keV/nm时。这也表明了材料中的自由基增多，可蚀刻性增大。随辐照剂量和电子能损的增大，材料逐渐碳化，同时有类苯环物质和炔基生成。炔基的生成有一个剂量阈值为5.5 * 10~(11)ions/cm~3，有一个电子能损阈值为0.61keV/nm。在紫外、可见谱中，380nm、450nm和500nm波长处的吸光度变化随电子能损按平方规律变化，随剂量按线性规律变化。

~(16)O + ~(28)Si全熔合激发函数研究及ΔE-E探测器系统的研制调试

ΔE-E望远镜探测器是用于重离子校反应测量的一种装置，它可以测量产物的电荷数和能量。在单路ΔE-E的基础上，我们研制了一路ΔE气体探测器和十路E金硅石垒探测器构成的多路ΔE-E望远镜探测系统。电离室窗直径为8cm，阴极到栅极距离为6cm，栅极到阳极距离为2cm，充入50的Ar(90%) + CH_4 (10%)气体，测得对~(241)Am的5.41Mev/α其能量分辩为13%。所用的十块金硅石垒探测器能量为1%左右。此系统可以同时测量22 °范围内的10个角度点，这对角分布测量将十分有利。该探测器系统对~(16)O + ~(12)C反应体的Z分辩约为6%，它可以清楚的分开C到Mg的各种元素。利用上述多路ΔE-E探测系统，我们测量了E_(16O) = 50Mev-90Mev的16_O束流轰击~RC、~(24)Mg、~(28)Si和~(32)S等四个体系校反应产物的角分布、能谱和激发函数。在测量激发函数时，我们选取能量步长为ΔE_(Lab) = 1Mev，以便观察振荡结构在角分布测量时，对于三个能量点，我们测量了5.1 °- 39 °范围内的13个角度点。由于时间限制，本毕业论文仅给出~(16)O + ~(28)Si反应的全熔合激发函数和角分布。并且运用G-M模型和Wiecki公式对全熔合截石进行了理论计算。从激发函曲线看，实验结果的平均趋势与G-M模型的理论结果符合的相当好，同时还发现了该体系全熔合截石随能量有规律的起伏，这种起伏具有公认的振荡结构和某些特征，因此这些起伏极有可能就是振荡结构

25MeV/A~(40)Ar+~(115)In反应中轻粒子发射研究及大面积位置灵敏闪烁探测器的研制

论文分为两个部分。第一部分：研究在25MeV/u ~(40)Ar+~(115)In反应中轻粒子发射机制。实验中，利用研制的轻粒子探测器测量了发射的P、#alpha#能谱。用三源模型拟合了轻粒子能谱，所提取的参数与费米气体模型的计算结果进行比较，分析了发射源形成和衰变的一些特点。第二部分：研制一种大面积幅度、时间、位置灵敏闪烁探测器。它是HIRFL上建成的第一阶段放射性核束物理实验终端的主要设备之一，在首次放射性核束调试中收到良好的效果。本文的目的是用经典理论研究了热核形成及衰变的一些性质，在即将开展的放射性核束物理研究中， 利用研制的大型探测器对经典理论普适性进行检验

25MeV/u~(40)Ar~(15+)+~(209)Bi反应的裂变研究

本文首先回顾了重离子物理学的发展简史，并介绍了当前的一些关于重离子反应的理论方法，同时对于现在核物理的研究热点，热核的特性进行了概括性的叙述．由于裂变是作者工作的重点，因此在文章中，对裂变反应的理论也进行了介绍．为了能够清楚全面的说明我们的工作，本文对于实验装置和探测器也给出了详细的描述．最后，文章对25 MeVu Ar+Bi反应中的裂变进行了讨论．在这些讨论中，我们分析了反应中与裂变相关的数据，得到了碎片的质量，动能分布。同时运用与碎片相关联的4He粒子能谱提取了核温度和裂前裂后的4He粒子多重性，并利用这一数据计算了不同初始激发能下的裂点激发能和裂变时标.

超铀区缺中子新核素~235 Am的合成与鉴别

本实验利用中国科学院高能物理研究所质子直线加速器提供的35MeV质子束流，轰击稀有放射性同位素靶238Pu，通过（p，4n）反应合成了超铀缺中子新核素235Am。反应产物是由氦喷嘴长毛细管传输系统传输和收集的，用快速化学分离方法分离出Am的同位素，使用两台高纯锗探测器对分离样品进行了X射线，γ射线和γ-γ（X）符合关系的测量，通过235Pu的衰变γ射线的生长——衰变趋势指定了235Am的生成，并通过Np的Kx射线的生长——衰变曲线确定了235Am的半衰期为（15±5）分钟。这是我国首次在超铀区合成缺中子新核素。