Q值效应对多核子转移反应136Xe+208Pb的影响

基于改进的量子分子动力学(ImQMD)模型，模拟了136Xe+208Pb在质心系入射能量为$E_{\rm{c.m.}}$=617 MeV的多核子转移反应。为了研究这个特殊的反应体系，将不同核子数转移前后形成的类弹与类靶对应的$Q$值的指数概率分布引入模型中考虑$Q$值效应，并将计算结果与实验探测的总动能损失分布和质量分布进行了比较。我们发现考虑$Q$值效应后的计算结果更好地再现了实验数据。在少于10个核子的转移过程中，核子的转移明显受到了$Q$值效应的驱动。在更多的核子转移过程中，$Q$值效应明显压低了反应产物的生成截面。这是因为大量的核子转移主要发生在小碰撞参数，对应的复合体系的寿命由于$Q$值效应明显减小。在ImQMD与ImQMD+Q的计算结果比较中，我们还发现，$Q$值效应明显增加了比208Pb更丰中子的中子数为126的初级碎块生成截面。     

Investigation of self-affine multiplicity fluctuations of proton emission in 84Kr-AgBr interactions at 1.7 A GeV

Self-affine multiplicity scaling is investigated in the framework of a two-dimensional factorial moment methodology using the concept of the Hurst exponent （H）. Investigation of the experimental data of medium-energy knocked-out target protons in ^84Kr-AgBr interactions at 1.7 AGeV reveals that the best power law behavior is exhibited for H=0.4, indicating a self-affine multiplicity fluctuation pattern. Multifractality among the knocked-out target protons is also observed in the data.     

Evidence of self-affine multiplicity fluctuation of target residues in ^84Kr-AgBr interactions at 1.7 AGeV

Self-affine multiplicity scaling is investigated in the framework of a two-dimensional factorial moment methodology using the concept of the Hurst exponent （H）. Analyzing the experimental data of target evaporated fragments emitted in ^84Kr-AgBr interactions at 1.7 AGeV revealed that the best power law behavior is exhibited for H = 0.3 indicating a self-arlene multiplicity fluctuation pattern. A signal of multifractality is also observed from knowledge of the anomalous fractal dimension dq extracted from the intermittency exponent aq of the anisotropic phase space scenario.     

Multiplicities of forward-backward particles in ^16O-emulsion interactions at 4.5 AGeV/c

An exclusive study of the characteristics of interactions accompanied by backward emission（θlab 90°） of shower and grey particles in collisions of a 4.5 AGeV/c ^16O beam with emulsion nuclei is carried out. The experimental multiplicity distributions of different particles emitted in the forward（θlab 〈 90°） and backward hemispheres due to the interactions with the two emulsion components（CNO,AgBr） are presented and analyzed. The correlations between the different emitted particles are also investigated. The results indicate that there are signatures for a collective mechanism,which plays a role in the production of particles in the backward hemisphere. Hence,the backward multiplicity distribution of the emitted shower and grey particles at 4.5 AGeV/c incident momentum can be represented by a decay exponential law formula independent of the projectile size. The exponent of the power was found to increase with decreasing target size. The experimental data favor the idea that the backward particles were emitted due to the decay of the system in the latter stages of the reactions.     

Experimental verification of therapeutic doses for the superficially-placed tumor radiotherapy with heavy ions at HIRFL

Up to now, clinical trials of heavy-ion radiotherapy for superficially placed tumors have been carried out for six times and over 60 selected patients have been treated with 80--100 MeV/u carbon ions supplied by the Heavy Ion Research Facility in Lanzhou （HIRFL） at the Institute of Modern Physics, Chinese Academy of Sciences since November, 2006. A passive irradiation system and a dose optimization method for radiotherapy with carbon-ion beams have been developed. Experimental verification of longitudinally therapeutic dose distributions was conducted under the condition of simulating patient treatment in the therapy terminal at HIRFL. The measured depth-dose distributions basically coincide with the expected ones. These results indicate that the irradiation system and the dose optimization method are effective in the ongoing carbon-ion radiotherapy for shallow-seated tumors at HIRFL.     

Influence of Ground State Spin of Projectile-Target on Fission Anisotropies

Fission fragment anisotropies have been investigated for various systems produced in heavy-ion reactions at near and sub-barrier energies. In particular, special attention has been paid to the entrance channel dependence of fragment angular anisotropies. The results of our analysis of the fragment angular anisotropies induced by boron, carbon, and oxygen ions on Thorium and Neptunium targets as well as Fluorine ions on Neptunium target indicate strong dependence of fragment anisotropies on the channel spin, in consistence with the predication of the pre-equilibrium model.     

QMD模型的改进及其在低能重离子反应中的应用

丰中子核以及重核熔合机制的研究以及中能重离子碰撞中多重碎裂的研究都迫切需要一个统一的、自洽的微观动力学模型.经过对量子分子动力学模型进行根本的改进,发展了一个新的、适用于低能以及中能重离子反应的统一描述的微观动力学模型.改进的量子分子动力学(ImQMD)模型能够将整个熔合反应过程中的动力学效应、同位旋效应以及弹靶质量不对称效应等比较全面地、自洽地考虑进来,从而给熔合反应的研究提供了一个新的途径.ImQMD模型能够很好地再现一系列核的基态性质以及10多个熔合反应的激发函数(包括丰中子核熔合体系以及实验最新测量的132Sn+64Ni熔合体系).此外还运用该模型初步探索了重核熔合过程中复合体系的寿命与体系的入射能量、体系大小以及体系的中子质子比的依赖关系. We have developed a new microscopic dynamical model called improved quantum molecular dynamical model (ImQMD). This model can describe the fusion process at energies near the Coulomb barrier as well as the multifragmentation process at intermediate energies in heavy-ion collision (HIC) uniformly. By using this model, fusion cross sections (including some of neutron-rich nuclei reactions and that of newly measured~(132)Sn+~(64)Ni fusion reaction) of tens reactions can be reproduced remarkably well. In fusi...     

Improved test of time dilation in special relativity

An improved test of time dilation in special relativity has been performed using laser spectroscopy on fast ions at the heavy-ion storage-ring TSR in Heidelberg. The Doppler-shifted frequencies of a two-level transition in 7Li+ ions at v=0.064c have been measured in the forward and backward direction to an accuracy of Deltanu/nu=1 x 10(-9) using collinear saturation spectroscopy. The result confirms the relativistic Doppler formula and sets a new limit of 2.2 x 10(-7) for deviations from the time dilation factor gamma(SR)=(1-v2/c2)(-1/2).     

Transport coefficients of a massive pion gas

We review our main results concerning the transport coefficients of a light meson gas,in particular we focus on the case of a massive pion gas.Leading order results according to the chiral power-counting are presented for the DC electrical conductivity,thermal conductivity,shear viscosity,and bulk viscosity.We also comment on the possible correlation between the bulk viscosity and the trace anomaly in QCD,as well as the relation between unitarity and a minimum of the quotient η/s near the phase transition.     

HEAVY ION COLLISIONS AND QUARK DISTRIBUTION IN NUCLEI

The heavy-ion collisions are studied by means of two-component Fokker-Planck equations on the assumption that there exist multiquark states in nuclei. Inclusive cross section for the production of p is calculated in heavy-ion collisions of C+C, Ne+NaF and Ar+KCI at 800 MeV/N; Ne+NaF at 400 MeV/N, 800 MeV/N and 2100 MeV/N. A satisfactory agreement with the experimental data near c.m. 90 degree is obtained. The production of d in the collision of C+C at 800 MeV/N is also discussed.     

Pauli exchange effects in the elastic scattering of O + O

The real optical potential for ¹⁶O+¹⁶O system is calculated within a generalized version of the double-folding model with the Pauli knock-on exchange effects between the projectile nucleons and the target nucleons taken into account from first principle. The elastic scattering data at E_lab=350 MeV supplemented by the new measurement at larger angles seem to be the first case in heavy-ion scattering where one can test the reliability of different theoretical heavy-ion optical potentials. Predictions are made for the elastic scattering of ¹⁶O+¹⁶O at laboratory energies of 240–480 MeV to illustrare the energy dependence of the rainbow structure which has been clearly observed in experiment at 350 MeV.     

RHIC能区Au+Au碰撞中集合径向流的研究

利用相对论量子分子动力学模型RQMD,对RHIC能区s=200A GeV Au+Au碰撞的集体膨胀效应进行了研究,对散射粒子的横质量谱进行了分析.研究表明,在RHIC能区的重离子反应中存在有强的集合径向流.对单粒子谱的拟合结果给出Au+Au的源冻结温度为160MeV,平均径向流速度为0.6c.     

Rho0 production and possible modification in Au+Au and p+p collisions at square root [sNN] = 200 GeV

We report results on rho(770)(0)-->pi(+)pi(-) production at midrapidity in p+p and peripheral Au+Au collisions at sqrt[s(NN)]=200 GeV. This is the first direct measurement of rho(770)(0)-->pi(+)pi(-) in heavy-ion collisions. The measured rho(0) peak in the invariant mass distribution is shifted by approximately 40 MeV/c(2) in minimum bias p+p interactions and approximately 70 MeV/c(2) in peripheral Au+Au collisions. The rho(0) mass shift is dependent on transverse momentum and multiplicity. The modification of the rho(0) meson mass, width, and shape due to phase space and dynamical effects are discussed.     

波包宽度对弹核碎裂反应截面的影响

运用改进的量子分子动力学(ImQMD)模型嫁接GEMINI统计衰变模型对波包宽度与弹核碎裂反应截面之间的关系进行了理论分析,分析了不同的波包宽度对400 AMeV 36Ar+C,20Ne与C,Al,Cu,Sn弹核碎裂反应截面的影响,分析了同位素36Ar,40Ar与Al反应在不同的波包宽度下的同位素分布。分析结果表明:波包宽度的选择影响着弹核碎裂的反应截面,并且与核反应体系有关。当σ2_r = 2 fm2时的计算结果与实验结果一致;而σ_r =(0.88+0.09 A1/3) fm的计算结果与体系有很大的关系,对弹核碎裂的反应截面影响明显。不的波包宽度对丰中子核40Ar的弹核碎裂反应截面的影响要小于对36Ar的弹核碎裂反应截面的影响,而且随体系分布的波包宽度计算的同位素要比σ2_r =2 fm2时计算的同位素多。The relations between wave packet width and projectile fragmentation cross sections are studied in theory by using the improved quantum molecular dynamics (ImQMD) and GEMINI models. The effect of different wave packet width for projectile fragmentation cross sections is analyzed for the reaction 36Ar on C, 20Ne on C, Al, Cu, Sn at 400 AMeV, the isotope distributions with different wave packet width are studied for reactions 36Ar, 40Ar on Al. The results show that the projectile fragmentation cross sections are affected by the choice of the wave packet width, and are related to the system of nuclear reaction. The calculation results of σ2_r =2 fm2are in agreement with the experimental results, but the results of σ_r = (0.88+0.09A1/3) fm have a strong relation with reaction system and the projectile fragmentation cross sections are affected obviously. The influence of wave packet width for 40Ar projectile fragmentation cross sections is smaller than that for 36Ar.Moreover isotope distributions with system-size-dependent wave packet width are larger than with σ2_r =2 fm2.     

Understanding of the dissipation mechanism in ternary fission for the system 197Au+197Au

The mass number distributions of three fragments from the ternary fission of the system 197Au+197Au are reproduced rather well by using the improved quantum molecular dynamics (ImQMD) model without any adjusting parameter. It is found that the probability of ternary fission evidently depends on the incident energy and the impact parameter, and the two-body dissipation is the main mechanism responsible for the formation of the third fragment with comparable mass.     

Possible Mechanisms of Ternary Fission in the 197Au+197Au System at 15 A MeV

Ternary fission in ^197Au＋^197Au collisions at 15 A MeV is investigated by using the improved quantum molecular dynamical （ImQMD） model. The experimental mass distributions for each of the three fragments are reproduced for the first time without any freely adjusting parameters. The mechanisms of ternary fission in central and semicentral collisions are dynamically studied. In direct prolate ternary fission, two necks are found to be formed almost simultaneously and rupture sequentially in a very short time interval. Direct oblate ternary fission is a very rare fission event, in which three necks are formed and rupture simultaneously, forming three equally sized fragments along space-symmetric directions in the reaction plane. In sequential ternary fission a binary division is followed by another binary fission event after hundreds of fm/c.     

Study on the pre-chopper in CSNS LEBT

Physical designing of the pre-chopper in CSNS LEBT is carried out, which includes the deflecting voltage, the length and the width of the deflecting plates, and the gap between the deflecting plates. The most outstanding feature of the design is that both the gap and the width vary with the beam envelope size. So both the requried deflecting voltage and the loaded capacitance are lowered. In order to avoid destruction of the space charge neutralization by the pre-chopper in the whole LEBT, an electron-trapping electrode is arranged to confine the electrostatic field of the pre-chopper to the local area. To examine the reliability of the pre-chopping design in CSNS LEBT, a similar pre-chopping design in ADS RFQ LEBT is set up and an experiment on the pre-chopper is prepared. 3-dimensional simulations are carried out to determine the loaded capacitance and the applied voltage of the electron-trapping electrode.     

Optimization and numerical simulation for the extraction system of the H- multicusp ion source

A new ion source has been designed and manufactured for the CYCLONE30 accelerator, which has a much advanced performance compared with the original. It is expected that the newly designed ion source extraction system will transport a very large percentage of the beam without deteriorating the beam optics, which is designed to deliver an H- beam at 30 keV. The accelerator assembly consists of three circular aperture electrodes made of copper. The simulation study was focused on finding parameter sets that raise the beam perveance as large as possible and which reduce the beam divergence as low as possible. Ion beams of the highest quality are extracted whenever the half-angular divergence is minimum, for which the perveance current intensity and the extraction gap have optimum values. The triode extraction system is designed and optimized by using CST software （for Particle Beam Simulations）. The physical design of the extraction system is given in this paper. From the simulation results, it is concluded that it is possible to achieve this goal by decreasing the thickness of the plasma electrode, shortening the first gap, and adjusting the acceleration electrode voltage.     

New results on the hadronic vacuum polarization contribution to the muon g－2

Results on the lowest-order hadronic vacuum polarization contribution to the muon magnetic anomaly are presented. They are based on the latest published experimental data used as input to the dispersion integral. Thus recent results on τ→υτππ^0 decays from Belle and on e^＋e^- annihilation to π^＋π^- from BABAR and KLOE are included. The new data, together with improved isospin-breaking corrections for τ decays, result into a much better consistency among the different results. A discrepancy between the Standard Model prediction and the direct g- 2 measurement is found at the level of 3σ.