2011年 第28卷 第4期
2011, 28(4): 377-395.
doi: 10.11804/NuclPhysRev.28.04.377
摘要:
对称能的密度依赖形式对于中子星结构及其演化规律、 不稳定核结构及其反应等都有非常重要的影响。 由于目前理论上预言的对称能密度依赖形式有很大的不确定性, 因此确定对称能的密度依赖形式已经成为目前核物理研究的一个重要课题。 丰中子核重离子碰撞是目前在实验室条件下确定对称能密度依赖形式的一种重要手段, 其主要的理论依据就是微观输运理论。 首先回顾了目前输运理论的两个处理方法, 即BoltzmannUehlingUhlenbeck(BUU)和量子分子动力学(QMD)方法, 并重点介绍了改进的量子分子动力学模型(ImQMD05)。 利用ImQMD05对中能重离子碰撞的一些基本观测量, 如碎块分布、 集体流、 核核碰撞的阻止本领等进行了详细研究, 通过与实验数据的比较, 确定了ImQMD05中同位旋无关部分的平均场、 介质中核子核子散射截面。 为了从重离子碰撞的实验数据确定对称能的密度依赖形式, 详细研究了输运理论中对称势以及同位旋相关的介质中核子核子散射截面对于同位旋敏感观测量的影响。 研究显示, 对于Fermi能附近的重离子碰撞, 输运理论预言的同位旋敏感的观测量, 如DR(n/p)和Ri, 强烈依赖于对称势的软硬, 而不敏感于介质中同位旋相关的核子核子散射截面。 多重碎裂作为中能重离子碰撞的一个主要特点, 本文论述的研究显示碎块发射机制对同位旋敏感的观测量, 出射核子的双中子质子之比DR(n/p)和同位旋转移之比Ri, 都有重要影响。 以重碎块的同位旋不对称度为探针得到的同位旋转移之比Ri (δZmax>20)要大于Ri(δ), 这些测量能够在NSCL/RIKEN的相关实验上进行测量。 同时, 这一现象的研究对于理解碎块的发射机制及碎块发射的特征时间等问题将有重要的帮助。 为此, 采用ImQMD05研究了112, 124Sn+112, 124Sn在入射能量50 MeV/u, 不同碰撞参数条件下的多个实验观测量, 如DR(n/p)、 同位旋扩散Ri以及同位旋转移之比的快度分布。 研究表明, 模型能够同时自洽地解释这几个实验观测量, 并通过与这些实验数据的分析比较, 自洽地确定出低密区对称能密度依赖形式的范围。 Nuclear symmetry energy plays an important role in the properties of nuclei and neutron stars. Since theoretical predictions of the density dependence of symmetry energy S(ρ) from microscopic nucleonnucleon interactions show large uncertainties, especially in the region of suprasaturation density, constraining the density dependence of symmetry energy has become one of the main goals in nuclear physics and has stimulated many theoretical and experimental studies. In this paper, we have reviewed the ImQMD05 code and its description on charge distribution, collective flow and nuclearnuclear stopping. By comparing ImQMD05 prediction with data, the isoscalar part of nucleonic mean field, the energy and density dependence of inmedium NN cross sectoin in the ImQMD05 were determined. In order to extracting the symmetry energy information by comparing the ImQMD05 calculations with the data for 112, 124Sn+112, 124 Sn at Ebeam=50 MeV/u, the influence of symmetry potential and inmedium NN cross section on the isospin sensitive observables of intermediateenergy heavyion collisions was investigated. Focusing on the region above the Fermi energy, our results show that the symmetry potential plays a more important role in the experimental observables, such as double neutron to proton ratio and the isospin transport ratio Ri, than that the inmedium nucleonnucleon cross section does. Since the copious production of intermediate mass fragments is a distinguishing feature of intermediateenergy heavyion collisions, we also examined the influence of cluster emission on the isospin transport ratio using different isospin tracers. The values of the isospin transport ratios with the tracer defined by the isospin asymmetry of the heaviest fragments with Z≥20 in the projectile region is greater than those obtained from projectile residues (emitting source). This phenomenon can be tested experimentally. By comparing the ImQMD05 predictions with the data for three observables, the selfconsistent constraints on the symmetry energy at subsaturation density were obtained.
对称能的密度依赖形式对于中子星结构及其演化规律、 不稳定核结构及其反应等都有非常重要的影响。 由于目前理论上预言的对称能密度依赖形式有很大的不确定性, 因此确定对称能的密度依赖形式已经成为目前核物理研究的一个重要课题。 丰中子核重离子碰撞是目前在实验室条件下确定对称能密度依赖形式的一种重要手段, 其主要的理论依据就是微观输运理论。 首先回顾了目前输运理论的两个处理方法, 即BoltzmannUehlingUhlenbeck(BUU)和量子分子动力学(QMD)方法, 并重点介绍了改进的量子分子动力学模型(ImQMD05)。 利用ImQMD05对中能重离子碰撞的一些基本观测量, 如碎块分布、 集体流、 核核碰撞的阻止本领等进行了详细研究, 通过与实验数据的比较, 确定了ImQMD05中同位旋无关部分的平均场、 介质中核子核子散射截面。 为了从重离子碰撞的实验数据确定对称能的密度依赖形式, 详细研究了输运理论中对称势以及同位旋相关的介质中核子核子散射截面对于同位旋敏感观测量的影响。 研究显示, 对于Fermi能附近的重离子碰撞, 输运理论预言的同位旋敏感的观测量, 如DR(n/p)和Ri, 强烈依赖于对称势的软硬, 而不敏感于介质中同位旋相关的核子核子散射截面。 多重碎裂作为中能重离子碰撞的一个主要特点, 本文论述的研究显示碎块发射机制对同位旋敏感的观测量, 出射核子的双中子质子之比DR(n/p)和同位旋转移之比Ri, 都有重要影响。 以重碎块的同位旋不对称度为探针得到的同位旋转移之比Ri (δZmax>20)要大于Ri(δ), 这些测量能够在NSCL/RIKEN的相关实验上进行测量。 同时, 这一现象的研究对于理解碎块的发射机制及碎块发射的特征时间等问题将有重要的帮助。 为此, 采用ImQMD05研究了112, 124Sn+112, 124Sn在入射能量50 MeV/u, 不同碰撞参数条件下的多个实验观测量, 如DR(n/p)、 同位旋扩散Ri以及同位旋转移之比的快度分布。 研究表明, 模型能够同时自洽地解释这几个实验观测量, 并通过与这些实验数据的分析比较, 自洽地确定出低密区对称能密度依赖形式的范围。 Nuclear symmetry energy plays an important role in the properties of nuclei and neutron stars. Since theoretical predictions of the density dependence of symmetry energy S(ρ) from microscopic nucleonnucleon interactions show large uncertainties, especially in the region of suprasaturation density, constraining the density dependence of symmetry energy has become one of the main goals in nuclear physics and has stimulated many theoretical and experimental studies. In this paper, we have reviewed the ImQMD05 code and its description on charge distribution, collective flow and nuclearnuclear stopping. By comparing ImQMD05 prediction with data, the isoscalar part of nucleonic mean field, the energy and density dependence of inmedium NN cross sectoin in the ImQMD05 were determined. In order to extracting the symmetry energy information by comparing the ImQMD05 calculations with the data for 112, 124Sn+112, 124 Sn at Ebeam=50 MeV/u, the influence of symmetry potential and inmedium NN cross section on the isospin sensitive observables of intermediateenergy heavyion collisions was investigated. Focusing on the region above the Fermi energy, our results show that the symmetry potential plays a more important role in the experimental observables, such as double neutron to proton ratio and the isospin transport ratio Ri, than that the inmedium nucleonnucleon cross section does. Since the copious production of intermediate mass fragments is a distinguishing feature of intermediateenergy heavyion collisions, we also examined the influence of cluster emission on the isospin transport ratio using different isospin tracers. The values of the isospin transport ratios with the tracer defined by the isospin asymmetry of the heaviest fragments with Z≥20 in the projectile region is greater than those obtained from projectile residues (emitting source). This phenomenon can be tested experimentally. By comparing the ImQMD05 predictions with the data for three observables, the selfconsistent constraints on the symmetry energy at subsaturation density were obtained.
2011, 28(4): 396-403.
doi: 10.11804/NuclPhysRev.28.04.396
摘要:
在带微观三体力的Brueckner-Hartree-Fock方法下研究了非对称核物质的不可压缩系数,得到了不可压缩系数的同位旋以及密度依赖, 并做了进一步的讨论。在一定密度下,不可压缩系数作为同位旋非对称度的函数随同位旋单调递增。 预测了非对称核物质在平衡态的同位旋依赖性质并与其他理论方法做了比较。 We have investigated the incompressibility of asymmetric nuclear matter within the BruecknerHartreeFock approach extended to include a microscopic threebody force. The isospindependence and densitydependence of the nuclear incompressibility have been obtained and discussed. It is shown that the incompressibility at a fixed density increases monotonically as a function of isospin asymmetry. The isospin asymmetry dependence of the equilibrium properties of asymmetric nuclear matter is also predicted and compared with the results of other theoretical approaches.
在带微观三体力的Brueckner-Hartree-Fock方法下研究了非对称核物质的不可压缩系数,得到了不可压缩系数的同位旋以及密度依赖, 并做了进一步的讨论。在一定密度下,不可压缩系数作为同位旋非对称度的函数随同位旋单调递增。 预测了非对称核物质在平衡态的同位旋依赖性质并与其他理论方法做了比较。 We have investigated the incompressibility of asymmetric nuclear matter within the BruecknerHartreeFock approach extended to include a microscopic threebody force. The isospindependence and densitydependence of the nuclear incompressibility have been obtained and discussed. It is shown that the incompressibility at a fixed density increases monotonically as a function of isospin asymmetry. The isospin asymmetry dependence of the equilibrium properties of asymmetric nuclear matter is also predicted and compared with the results of other theoretical approaches.
2011, 28(4): 404-407.
doi: 10.11804/NuclPhysRev.28.04.404
摘要:
在核吸收与随动者吸收理论的基础上, 给出了在有QGP相变情况下高能重离子碰撞中的J/Ψ微分产生截面,并用其讨论了CERN的NA50合作组给出的入射动量为158 AGeV/c 的Pb-Pb碰撞中的J/Ψ反常抑制现象。理论较好地解释了实验结果。On the basis of nuclear and comover absorption theories, we have derived out the differential cross section of J/Ψ production in high-energy heavy-ion collisions under the situation that QGP phase transition occurs, and analyzed the experimental data of NA50 Collaboration at CERN in Pb-Pb collisions at 158 AGeV/c. Our theory favors the data well.
在核吸收与随动者吸收理论的基础上, 给出了在有QGP相变情况下高能重离子碰撞中的J/Ψ微分产生截面,并用其讨论了CERN的NA50合作组给出的入射动量为158 AGeV/c 的Pb-Pb碰撞中的J/Ψ反常抑制现象。理论较好地解释了实验结果。On the basis of nuclear and comover absorption theories, we have derived out the differential cross section of J/Ψ production in high-energy heavy-ion collisions under the situation that QGP phase transition occurs, and analyzed the experimental data of NA50 Collaboration at CERN in Pb-Pb collisions at 158 AGeV/c. Our theory favors the data well.
2011, 28(4): 408-415.
doi: 10.11804/NuclPhysRev.28.04.408
摘要:
简要综述了中高能重离子碰撞中K介子的产生及研究进展。重点介绍了K介子协变动力学模型, 并在此框架内分析了中高能重离子碰撞中K+介子以及与其伴随产生的Λ超子的集体流特征。 结果表明: 协变动力学模型能够很好地给出K+介子和Λ超子的微分直接流。 相对而言, 软势给出的集体流与实验值符合更好。同时, 通过对不同输运模型中K介子准粒子模型的基本属性进行对比分析, 明确了协变动力学模型中K介子准粒子模型的质量及能量随核物质密度的变化特征, 以及周围核子的运动对于K介子基本属性的影响。In the present paper, we briefly review the progress in the study of kaon production in heavy\|ion collisions at intermediate and high energies and introduce the covariant kaon dynamics model. The collective flows of positively charged kaon and the lambda hyperon associated produced with kaon are studied in the framework of the dynamics. It shows that the directed differential flow of K+ meson and Λ hyperon can be reasonably reproduced in the covariant kaon dynamics model. The calculated results with soft equation of nuclear matter are in better agrement with experimental data. Meawhile, a detailed comparison of the properites of different quasi\|particle models in various transport model and the influence of nucleon’s movement on the effective mass and energy of the quasi\|particle in the covariant kaon dynamics model are discussed.
简要综述了中高能重离子碰撞中K介子的产生及研究进展。重点介绍了K介子协变动力学模型, 并在此框架内分析了中高能重离子碰撞中K+介子以及与其伴随产生的Λ超子的集体流特征。 结果表明: 协变动力学模型能够很好地给出K+介子和Λ超子的微分直接流。 相对而言, 软势给出的集体流与实验值符合更好。同时, 通过对不同输运模型中K介子准粒子模型的基本属性进行对比分析, 明确了协变动力学模型中K介子准粒子模型的质量及能量随核物质密度的变化特征, 以及周围核子的运动对于K介子基本属性的影响。In the present paper, we briefly review the progress in the study of kaon production in heavy\|ion collisions at intermediate and high energies and introduce the covariant kaon dynamics model. The collective flows of positively charged kaon and the lambda hyperon associated produced with kaon are studied in the framework of the dynamics. It shows that the directed differential flow of K+ meson and Λ hyperon can be reasonably reproduced in the covariant kaon dynamics model. The calculated results with soft equation of nuclear matter are in better agrement with experimental data. Meawhile, a detailed comparison of the properites of different quasi\|particle models in various transport model and the influence of nucleon’s movement on the effective mass and energy of the quasi\|particle in the covariant kaon dynamics model are discussed.
2011, 28(4): 416-422.
doi: 10.11804/NuclPhysRev.28.04.416
摘要:
With an oscillator basis, the nuclear Hamiltonian is defined in a nocore model space. It consists of an effective nucleonnucleon interaction obtained with Brueckner theory from the Reid soft core interaction, a Coulomb potential, nucleondelta transition potentials, and deltadelta interaction terms. By performing spherical HartreeFock (SHF) calculations with the realistic baryon Hamiltonian, the ground state properties of 40Ca are studied. For an estimate of how the delta degree of freedom is excited, SHF calculations are performed with a radial constraint to compress the nucleus. The delta degree of freedom is gradually populated as the nucleus is compressed. The number of Δ’s is decreased by increasing model space. Large amount of the compressive energy is delivered to create massive Δ in the nucleus. There is a significant reduction in the static compression modulus for RSC static compressions which is reduced by including the Δ excitations. The static compression modulus is decreased significantly by en larging the nucleon model space. The results suggest that inclusion of the delta in the nuclear dynamics could head to a significant softening of the nuclear equation of state.
With an oscillator basis, the nuclear Hamiltonian is defined in a nocore model space. It consists of an effective nucleonnucleon interaction obtained with Brueckner theory from the Reid soft core interaction, a Coulomb potential, nucleondelta transition potentials, and deltadelta interaction terms. By performing spherical HartreeFock (SHF) calculations with the realistic baryon Hamiltonian, the ground state properties of 40Ca are studied. For an estimate of how the delta degree of freedom is excited, SHF calculations are performed with a radial constraint to compress the nucleus. The delta degree of freedom is gradually populated as the nucleus is compressed. The number of Δ’s is decreased by increasing model space. Large amount of the compressive energy is delivered to create massive Δ in the nucleus. There is a significant reduction in the static compression modulus for RSC static compressions which is reduced by including the Δ excitations. The static compression modulus is decreased significantly by en larging the nucleon model space. The results suggest that inclusion of the delta in the nuclear dynamics could head to a significant softening of the nuclear equation of state.
2011, 28(4): 423-427.
doi: 10.11804/NuclPhysRev.28.04.423
摘要:
基态双质子衰变是质子滴线区原子核的一种奇异衰变。 它可以揭示质子滴线区原子核外层质子对的结构行为, 检验现有核模型理论应用于极端条件下原子核的正确性。 搜索基态双质子衰变是人们广泛关注的一个实验难题, 直到理论预言提出后40多年才取得明显进展。 简要介绍了这一研究的进展情况。 The ground-state two-proton decay is an exotic decay beyond proton drip line. It deals with the structure behavior of the proton pair at outside orbital in a proton dripline nucleus, and can be used to check the current nuclear model under extreme condition. Experimental observation of groundstate twoproton decay has been widely considered as a challenge because of very low production cross section. In this short paper, the breakthrough of searching groundstate twoproton decay is briefly reviewed, which was made more than 40 years after the early theoretical prediction was proposed.
基态双质子衰变是质子滴线区原子核的一种奇异衰变。 它可以揭示质子滴线区原子核外层质子对的结构行为, 检验现有核模型理论应用于极端条件下原子核的正确性。 搜索基态双质子衰变是人们广泛关注的一个实验难题, 直到理论预言提出后40多年才取得明显进展。 简要介绍了这一研究的进展情况。 The ground-state two-proton decay is an exotic decay beyond proton drip line. It deals with the structure behavior of the proton pair at outside orbital in a proton dripline nucleus, and can be used to check the current nuclear model under extreme condition. Experimental observation of groundstate twoproton decay has been widely considered as a challenge because of very low production cross section. In this short paper, the breakthrough of searching groundstate twoproton decay is briefly reviewed, which was made more than 40 years after the early theoretical prediction was proposed.
2011, 28(4): 428-432.
doi: 10.11804/NuclPhysRev.28.04.428
摘要:
实验通过17F+p共振弹性散射研究了复合核18Ne激发态中与天体核反应14O(α, p)17F相关的共振态性质。利用兰州放射性束流线(RIBLL)对弹核碎裂反应产生的放射性束17F进行了分离和提纯。经过降能后,能量为4.22 AMeV 的17F束流轰击在T2终端的厚氢靶(CH2)n上。 两套∆E-E Si探测器望远镜放置在两个不同的探测角度θlab≈2.3°和14°上,对反冲质子的角度和能量进行了测量。实验观测到了复合核18Ne的几条质子共振能级。通过R-Matrix理论程序对激发函数进行拟合,得到了共振态的能量、 自旋、 宇称和衰变宽度等共振参数。Resonant properties in18Ne relevant to the stellar reaction of 14O(α, p)17F have been investigated through a resonant elastic scattering of 17F+p. The 17F RI beam was produced via a projectilefragmentation reaction, and subsequently separated and purified by Radioactive Ion beam Line in Lanzhou(RIBLL). After a series of energy degradation,a 4.22 AMeV 17F beam bombarded a thick(CH2)ntarget at T2 terminal. Energy and angle of the recoiled protons were measured by two sets of ∆E-E silicon telescope at θlab≈2.3°,14° respectively. Several resonances in 18Ne were observed,and their resonant parametersincluding energy,spinparity and decay width have been determined by an R-Matrix analysis of the experimental excitation function.
实验通过17F+p共振弹性散射研究了复合核18Ne激发态中与天体核反应14O(α, p)17F相关的共振态性质。利用兰州放射性束流线(RIBLL)对弹核碎裂反应产生的放射性束17F进行了分离和提纯。经过降能后,能量为4.22 AMeV 的17F束流轰击在T2终端的厚氢靶(CH2)n上。 两套∆E-E Si探测器望远镜放置在两个不同的探测角度θlab≈2.3°和14°上,对反冲质子的角度和能量进行了测量。实验观测到了复合核18Ne的几条质子共振能级。通过R-Matrix理论程序对激发函数进行拟合,得到了共振态的能量、 自旋、 宇称和衰变宽度等共振参数。Resonant properties in18Ne relevant to the stellar reaction of 14O(α, p)17F have been investigated through a resonant elastic scattering of 17F+p. The 17F RI beam was produced via a projectilefragmentation reaction, and subsequently separated and purified by Radioactive Ion beam Line in Lanzhou(RIBLL). After a series of energy degradation,a 4.22 AMeV 17F beam bombarded a thick(CH2)ntarget at T2 terminal. Energy and angle of the recoiled protons were measured by two sets of ∆E-E silicon telescope at θlab≈2.3°,14° respectively. Several resonances in 18Ne were observed,and their resonant parametersincluding energy,spinparity and decay width have been determined by an R-Matrix analysis of the experimental excitation function.
2011, 28(4): 433-438.
doi: 10.11804/NuclPhysRev.28.04.433
摘要:
Wigner函数在对量子体系状态的描述方面具有重要的意义。 讨论了自旋1/2非对易朗道问题的Wigner函数。首先回顾了对易空间中Wigner函数所服从的星本征方程, 然后给出了非对易相空间中自旋1/2朗道问题的Hamiltonian, 最后利用星本征方程(Moyal 方程)计算了非对易相空间中自旋1/2朗道问题具有矩阵表示形式的Wigner函数及其能级。With great significance in describing the state of quantum system, the Wigner function of the spin half noncommutative Landau problem is studied in this paper. On the basis of the review of the Wigner function in the commutative space, which is subject to the *eigenvalue equation, Hamiltonian of the spin half Landau problem in the noncommutative phase space is given. Then, energy levels and Wigner functions in the form of a matrix of the spin half Landau problem in the noncommutative phase space are obtained by means of the *-eigenvalue equation (or Moyal equation).
Wigner函数在对量子体系状态的描述方面具有重要的意义。 讨论了自旋1/2非对易朗道问题的Wigner函数。首先回顾了对易空间中Wigner函数所服从的星本征方程, 然后给出了非对易相空间中自旋1/2朗道问题的Hamiltonian, 最后利用星本征方程(Moyal 方程)计算了非对易相空间中自旋1/2朗道问题具有矩阵表示形式的Wigner函数及其能级。With great significance in describing the state of quantum system, the Wigner function of the spin half noncommutative Landau problem is studied in this paper. On the basis of the review of the Wigner function in the commutative space, which is subject to the *eigenvalue equation, Hamiltonian of the spin half Landau problem in the noncommutative phase space is given. Then, energy levels and Wigner functions in the form of a matrix of the spin half Landau problem in the noncommutative phase space are obtained by means of the *-eigenvalue equation (or Moyal equation).
2011, 28(4): 439-443.
doi: 10.11804/NuclPhysRev.28.04.439
摘要:
介绍了现阶段两种用于聚焦离子束系统的离子源——液态金属离子源和气体场发射离子源的基本原理, 并对比了它们的优缺点。由于目前这两种离子源都难以满足纳米加工领域不断提高的技术要求, 因此提出了一种用于聚焦离子束的新型离子源——电子束离子源, 并介绍了电子束离子源的基本原理, 给出了设计参数、 模拟结果(20 kV的Ar+离子束, 发射度约为5.8×10-5·mm·mrad, 束斑约为1 μm)和初步的实验结果。 There are two kinds of ion sources, LiquidMetal Ion Source and Gas Field Ion Source, used to provide ion beams for the Focus Ion Beam system. The working mechanism of the two kinds of sources is presented and their advantages and disadvantages are summarized. With the rapid development in the nano technology, the requirements are hardly met with these two kinds of ion sources. Therefore, a new kind of ion source, electron beam ion source, is developed for the Focus Ion Beam system. The basic principle of the electron beam ion source is introduced and the design parameters, the result of the simulation (20 kV Ar+, extracted emittance is 5.8×10-5π·mm·mrad, raduis of the ion beam about 1 μm.) and the primary experimental results are presented
介绍了现阶段两种用于聚焦离子束系统的离子源——液态金属离子源和气体场发射离子源的基本原理, 并对比了它们的优缺点。由于目前这两种离子源都难以满足纳米加工领域不断提高的技术要求, 因此提出了一种用于聚焦离子束的新型离子源——电子束离子源, 并介绍了电子束离子源的基本原理, 给出了设计参数、 模拟结果(20 kV的Ar+离子束, 发射度约为5.8×10-5·mm·mrad, 束斑约为1 μm)和初步的实验结果。 There are two kinds of ion sources, LiquidMetal Ion Source and Gas Field Ion Source, used to provide ion beams for the Focus Ion Beam system. The working mechanism of the two kinds of sources is presented and their advantages and disadvantages are summarized. With the rapid development in the nano technology, the requirements are hardly met with these two kinds of ion sources. Therefore, a new kind of ion source, electron beam ion source, is developed for the Focus Ion Beam system. The basic principle of the electron beam ion source is introduced and the design parameters, the result of the simulation (20 kV Ar+, extracted emittance is 5.8×10-5π·mm·mrad, raduis of the ion beam about 1 μm.) and the primary experimental results are presented
2011, 28(4): 444-447.
doi: 10.11804/NuclPhysRev.28.04.444
摘要:
在HIRFL-CSRm上进行高能量密度物理和等离子体物理的研究需要一个能提供高电压的高频腔来对束团进行纵向压缩, 而磁合金加载腔获得较高的加速场梯度可以满足这一要求, 且腔体不需要调谐, 从而简化了高频控制系统。为了选择磁导率和阻抗较大、Q值(品质因数)小于1的磁合金材料来加载压缩高频腔, 对型号为V和A的两种磁合金材料进行了测试。测试结果表明: 型号为V的材料具有较大的磁导率、 阻抗和小于1的Q值, 将被用来加载腔体以获得足够高的加速电场梯度。A high voltage RF cavity is required to compress the beam bunch in the longitudinal for high energy density physics and plasma physics research at HIRFLCSRm. A magnetic alloy (MA)loaded cavity which has high acceleration gradient and without tuning loop (can simplify the RF control system), can meet the requirement. In order to select a proper MA material with higher permeability and shunt impe dance, Q< 1 value to load the RF compression cavity, two different MA materials V and A have been tes ted. The results indicate that the material V will be better for the construction of the RF cavity than material A because of its higher permeability and shunt impedance, Q< 1 value.
在HIRFL-CSRm上进行高能量密度物理和等离子体物理的研究需要一个能提供高电压的高频腔来对束团进行纵向压缩, 而磁合金加载腔获得较高的加速场梯度可以满足这一要求, 且腔体不需要调谐, 从而简化了高频控制系统。为了选择磁导率和阻抗较大、Q值(品质因数)小于1的磁合金材料来加载压缩高频腔, 对型号为V和A的两种磁合金材料进行了测试。测试结果表明: 型号为V的材料具有较大的磁导率、 阻抗和小于1的Q值, 将被用来加载腔体以获得足够高的加速电场梯度。A high voltage RF cavity is required to compress the beam bunch in the longitudinal for high energy density physics and plasma physics research at HIRFLCSRm. A magnetic alloy (MA)loaded cavity which has high acceleration gradient and without tuning loop (can simplify the RF control system), can meet the requirement. In order to select a proper MA material with higher permeability and shunt impe dance, Q< 1 value to load the RF compression cavity, two different MA materials V and A have been tes ted. The results indicate that the material V will be better for the construction of the RF cavity than material A because of its higher permeability and shunt impedance, Q< 1 value.
2011, 28(4): 448-453.
doi: 10.11804/NuclPhysRev.28.04.448
摘要:
强流脉冲束传输的计算是一个相当复杂的问题, 因为不同类型的粒子束分布产生不同的空间电荷场, 而在束流运动过程中, 空间电荷场也在不断地变化, 而且粒子运动的轨迹与空间电荷势又是相互依赖的, 因此需要求得一个自洽解。采用矩阵法分析了非强流脉冲束流与强流脉冲束流在四极磁铁中传输的矩阵, 并编写了束流在四极磁铁等元件中的传输计算程序, 程序采用迭代计算方法获得自洽解。程序运行时, 可以进行直观的图形显示。It is very difficalt to calculate the nonlinear transport of a intense beam, because the particle trajectories depend on the electric potentials excited by the particle beams, and the electric potentials of the beams depend on the particle trajectories and the particle distributions in the phase spaces. So, it is necessary to solve the problem by iterations to get selfconsistent solutions.We use transport matrix method to analyze the transportation in quadrupole magnet of nonintense pulsed beam and intense pulsed beam respectively, and write a computer code for the pulsed beam transporting in quadrupole magnet. The selfconsistent solution can obtained by using iteration calculation method. During the calculation, the result can be shown by the prompt graph.
强流脉冲束传输的计算是一个相当复杂的问题, 因为不同类型的粒子束分布产生不同的空间电荷场, 而在束流运动过程中, 空间电荷场也在不断地变化, 而且粒子运动的轨迹与空间电荷势又是相互依赖的, 因此需要求得一个自洽解。采用矩阵法分析了非强流脉冲束流与强流脉冲束流在四极磁铁中传输的矩阵, 并编写了束流在四极磁铁等元件中的传输计算程序, 程序采用迭代计算方法获得自洽解。程序运行时, 可以进行直观的图形显示。It is very difficalt to calculate the nonlinear transport of a intense beam, because the particle trajectories depend on the electric potentials excited by the particle beams, and the electric potentials of the beams depend on the particle trajectories and the particle distributions in the phase spaces. So, it is necessary to solve the problem by iterations to get selfconsistent solutions.We use transport matrix method to analyze the transportation in quadrupole magnet of nonintense pulsed beam and intense pulsed beam respectively, and write a computer code for the pulsed beam transporting in quadrupole magnet. The selfconsistent solution can obtained by using iteration calculation method. During the calculation, the result can be shown by the prompt graph.
2011, 28(4): 454-458.
doi: 10.11804/NuclPhysRev.28.04.454
摘要:
在经典力学框架内和偶极近似下,引入正弦平方势,把粒子运动方程化为具有阻尼项和受迫项的广义摆方程。利用Melnikov方法讨论了沟道运动次谐分叉及其稳定性, 导出了周期弯晶的临界条件和退道长度。结果表明, 要试图获得高的引出效率, 除了要求弯晶长度必须小于退道长度外, 还必须保证沟道粒子的运动是稳定的。对临界条件的分析表明, 系统的稳定性与它的参数有关, 只须适当调节系统参数, 就可以保证周期弯晶作为引出元件的稳定性。
In the classical mechanics frame and with a dipole approximation the particle motion equation in the periodic bent crystal is reduced to the general pendulum equation with a damping term and the forced term by using the sinesquared potential. This paper discusses the problem of the subharmonic bifurcation of the periodic orbit and the stabilities of the channeling motion by using Melnikov method, so as to derive the critical condition and the dechanneling length of the periodic bent crystal. The results show that channeling motion must be stable in addition that the crystal length is smaller than the dechanneling length in order to ensure higher extracted efficiency. The analysis of the critical condition shows that the system stabilities are related to its parameters. Just by properly regulating the parameters of the system, the dynamic stabilities by the use of periodic bent crystal as beam control cell can be ensured.
在经典力学框架内和偶极近似下,引入正弦平方势,把粒子运动方程化为具有阻尼项和受迫项的广义摆方程。利用Melnikov方法讨论了沟道运动次谐分叉及其稳定性, 导出了周期弯晶的临界条件和退道长度。结果表明, 要试图获得高的引出效率, 除了要求弯晶长度必须小于退道长度外, 还必须保证沟道粒子的运动是稳定的。对临界条件的分析表明, 系统的稳定性与它的参数有关, 只须适当调节系统参数, 就可以保证周期弯晶作为引出元件的稳定性。
In the classical mechanics frame and with a dipole approximation the particle motion equation in the periodic bent crystal is reduced to the general pendulum equation with a damping term and the forced term by using the sinesquared potential. This paper discusses the problem of the subharmonic bifurcation of the periodic orbit and the stabilities of the channeling motion by using Melnikov method, so as to derive the critical condition and the dechanneling length of the periodic bent crystal. The results show that channeling motion must be stable in addition that the crystal length is smaller than the dechanneling length in order to ensure higher extracted efficiency. The analysis of the critical condition shows that the system stabilities are related to its parameters. Just by properly regulating the parameters of the system, the dynamic stabilities by the use of periodic bent crystal as beam control cell can be ensured.
2011, 28(4): 459-463.
doi: 10.11804/NuclPhysRev.28.04.459
摘要:
介绍了微型网状结构的气体探测器一维位置编码读出的基本原理和实现方法。设计了一块灵敏面积为10 cm×10 cm的一维位置编码PCB读出电极。测试表明: 感应读出是可行的, 电荷按1∶2分配最为理想; 利用55Fe放射源X射线通过200 μm狭缝对准读出电极PCB板的正面中任意一条, 位置编码读出能很好地再现源所在狭缝的位置。针对其局限性, 提出了一维位置分组编码读出技术, 以解决相邻多条同时点火的情况。使用该读出技术, 使一维读出电子学路数节省量达到75%以上。
The basic principles and implementation of onedimensional position encoding readout for MICROMEGAS have been introduced in this paper. A 10 cm×10 cm prototype of onedimensional position encoding readout electrode based on printed circuit board was designed. Preliminary test indicates that the induction readout is feasible and the ideal charge distribution is 1∶2. X rays emitted from 55Fe source were collimated to one of strips on the readout electrode through a slit of 200 μm, position decoding well reproduced the position of the 55Fe source. For its limitations, we have proposed a onedimensional grouped position encoding readout technique to address a neighboring strips simultaneously fired situation. The amount of readout electronics is very easy to approach a obduction of 75% with position encoding read out technology.
介绍了微型网状结构的气体探测器一维位置编码读出的基本原理和实现方法。设计了一块灵敏面积为10 cm×10 cm的一维位置编码PCB读出电极。测试表明: 感应读出是可行的, 电荷按1∶2分配最为理想; 利用55Fe放射源X射线通过200 μm狭缝对准读出电极PCB板的正面中任意一条, 位置编码读出能很好地再现源所在狭缝的位置。针对其局限性, 提出了一维位置分组编码读出技术, 以解决相邻多条同时点火的情况。使用该读出技术, 使一维读出电子学路数节省量达到75%以上。
The basic principles and implementation of onedimensional position encoding readout for MICROMEGAS have been introduced in this paper. A 10 cm×10 cm prototype of onedimensional position encoding readout electrode based on printed circuit board was designed. Preliminary test indicates that the induction readout is feasible and the ideal charge distribution is 1∶2. X rays emitted from 55Fe source were collimated to one of strips on the readout electrode through a slit of 200 μm, position decoding well reproduced the position of the 55Fe source. For its limitations, we have proposed a onedimensional grouped position encoding readout technique to address a neighboring strips simultaneously fired situation. The amount of readout electronics is very easy to approach a obduction of 75% with position encoding read out technology.
2011, 28(4): 464-468.
doi: 10.11804/NuclPhysRev.28.04.464
摘要:
描述了一种适用于阵列探测器的数据获取系统。系统基于PXI总线, 采用标准NIM插件作为前端电子学。系统软件采用C/C++语言编写, 在线分析通过调用ROOT类库实现, 系统运行在Linux操作系统下。多次测试结果表明, 系统稳定可靠, 单个ADC通道可以处理的最大事例率为40 kHz。A data acquisition system for array detectors is described. The system is based on PXI bus with standard NIM modules used as front\|end electronics. The system software is written in C/C++ language with its online analysis modules realized by ROOT class library. Several runs of the system under Linux show that it is reliable and is capable of handling event rates up to 40 k events/s for 1 ADC channel.
描述了一种适用于阵列探测器的数据获取系统。系统基于PXI总线, 采用标准NIM插件作为前端电子学。系统软件采用C/C++语言编写, 在线分析通过调用ROOT类库实现, 系统运行在Linux操作系统下。多次测试结果表明, 系统稳定可靠, 单个ADC通道可以处理的最大事例率为40 kHz。A data acquisition system for array detectors is described. The system is based on PXI bus with standard NIM modules used as front\|end electronics. The system software is written in C/C++ language with its online analysis modules realized by ROOT class library. Several runs of the system under Linux show that it is reliable and is capable of handling event rates up to 40 k events/s for 1 ADC channel.
2011, 28(4): 469-473.
doi: 10.11804/NuclPhysRev.28.04.469
摘要:
建立了一套门控闪烁测量系统(门控ST-PMT系统), 测量了稠密等离子体聚焦(DPF)波形后沿中子峰下3~4个量级的物理图像, 分别讨论了长电缆对 DPF D-D, D-T中子峰下3~4个量级波形测量的影响, 采用数学方法分析了长电缆作为频率滤波函数在解逆卷积函数中的应用, 解析了电缆带宽对测量结果的影响。The influence of the Fourier Transform on long cable in the measurement of fall time of DPF neutron profile is discussed by mathematical methods. The application of anticonvolution function with the Fourier Transform on long cable is analysed. The time interval between the peak
time and the time that the height falls 3 orders of magnitude after peak is measured with gateddetector array system which consists of PMT(photomultiplier tube) and organic scintillation crystal.
建立了一套门控闪烁测量系统(门控ST-PMT系统), 测量了稠密等离子体聚焦(DPF)波形后沿中子峰下3~4个量级的物理图像, 分别讨论了长电缆对 DPF D-D, D-T中子峰下3~4个量级波形测量的影响, 采用数学方法分析了长电缆作为频率滤波函数在解逆卷积函数中的应用, 解析了电缆带宽对测量结果的影响。The influence of the Fourier Transform on long cable in the measurement of fall time of DPF neutron profile is discussed by mathematical methods. The application of anticonvolution function with the Fourier Transform on long cable is analysed. The time interval between the peak
time and the time that the height falls 3 orders of magnitude after peak is measured with gateddetector array system which consists of PMT(photomultiplier tube) and organic scintillation crystal.
2011, 28(4): 474-478.
doi: 10.11804/NuclPhysRev.28.04.474
摘要:
采用电子束(EB)对聚丙烯腈/聚氧化乙烯(PAN/PEO)凝胶电解质进行了剂量为13~260 kGy的辐照, 并对辐照改性的电解质组装的染料敏化太阳电池(DSSC)进行了性能测量。 结果表明, 改性后的DSSC的光电转化效率比改性前的高; 并且随EB辐照剂量的增加, DSSC效率先迅速增加(0~65 kGy), 然后缓慢减小(65~130 kGy)直至趋于一个平衡值(130~260 kGy)。 提升DSSC效率的最佳辐照剂量为65 kGy, 此时效率提高了约36%。 对比DSSC短路电流、 开路电压和填充因子随辐照剂量的变化, 发现DSSC效率的提高主要是由短路电流的提高引起的。 测量表明, 辐照改性后的DSSC时间稳定性得到了改善, 并且辐照剂量越高, 稳定性的改善越明显。
In this work, PAN/PEO (polyacrylonitrile/polyethylene oxide)based gel electrolyte was irradiated by electron beam (EB) with dose from 13 to 260 kGy. Then, DSSC (dyesensitized solar cell) was fabricated by the irradiated electrolyte and characterized. The results show that the efficiency of the DSSC fabricated by irradiated electrolyte is promoted comparing with DSSC fabricated by unirradiated electrolyte. And with irradiation dose increasing, the DSSC efficiency increases rapidly at first (0~65 kGy), then, drops down slowly (65~130 kGy), finally trends to a stable value (130~260 kGy). It indicates that there is an optimal irradiation dose, at which the promotion of DSSC efficiency is the highest, approximate 36%. Observed from the change of shortcircuit current, opencircuit voltage and fill factor, shortcircuit current promotion by EB irradiation is found to be the main reason of DSSC performance promotion. The time stability measurement of the DSSC indicates that EB irradiation on PAN/PEO electrolyte reduces the loss of efficiency and the limitingeffects become more apparent as the irradiation dose increases.
采用电子束(EB)对聚丙烯腈/聚氧化乙烯(PAN/PEO)凝胶电解质进行了剂量为13~260 kGy的辐照, 并对辐照改性的电解质组装的染料敏化太阳电池(DSSC)进行了性能测量。 结果表明, 改性后的DSSC的光电转化效率比改性前的高; 并且随EB辐照剂量的增加, DSSC效率先迅速增加(0~65 kGy), 然后缓慢减小(65~130 kGy)直至趋于一个平衡值(130~260 kGy)。 提升DSSC效率的最佳辐照剂量为65 kGy, 此时效率提高了约36%。 对比DSSC短路电流、 开路电压和填充因子随辐照剂量的变化, 发现DSSC效率的提高主要是由短路电流的提高引起的。 测量表明, 辐照改性后的DSSC时间稳定性得到了改善, 并且辐照剂量越高, 稳定性的改善越明显。
In this work, PAN/PEO (polyacrylonitrile/polyethylene oxide)based gel electrolyte was irradiated by electron beam (EB) with dose from 13 to 260 kGy. Then, DSSC (dyesensitized solar cell) was fabricated by the irradiated electrolyte and characterized. The results show that the efficiency of the DSSC fabricated by irradiated electrolyte is promoted comparing with DSSC fabricated by unirradiated electrolyte. And with irradiation dose increasing, the DSSC efficiency increases rapidly at first (0~65 kGy), then, drops down slowly (65~130 kGy), finally trends to a stable value (130~260 kGy). It indicates that there is an optimal irradiation dose, at which the promotion of DSSC efficiency is the highest, approximate 36%. Observed from the change of shortcircuit current, opencircuit voltage and fill factor, shortcircuit current promotion by EB irradiation is found to be the main reason of DSSC performance promotion. The time stability measurement of the DSSC indicates that EB irradiation on PAN/PEO electrolyte reduces the loss of efficiency and the limitingeffects become more apparent as the irradiation dose increases.
2011, 28(4): 479-484.
doi: 10.11804/NuclPhysRev.28.04.479
摘要:
由于低能离子较低的组织穿透能力, 其诱变机理一直是研究者争论的问题。 近年来, 本研究组的一系列研究工作已经证明在植物中存在辐射远程(诱变)效应, 从一个新的角度解释了低能离子的诱变机理, 然而依然无法解释低能离子辐照中的许多独特生物现象, 而这些现象均具有明显的表观遗传学特性。 以表观遗传学最具标志性特征的胞嘧啶甲基化为研究对象, 以α粒子拟南芥菜根辐照实验体系作为研究平台, 检测了远程组织(器官)甲基化相关基因 AtDML3 的表达及特定基因片段的甲基化水平。 研究证实, 在植物个体水平辐射可以诱导远程表观遗传的变化, 为进一步探索低能离子的诱变机理提供了新的思路。 Along the way, the mutagenic mechanism of lowenergy ions irradiation is a debatable issue. Recently, the existence of radiation induced longrange (mutagenic) effects in vivo in plants has been performed in a series of studies of our group, which account for the mutagenesis of lowenergy ions irradiation in a new perspective. However, numerous distinct biology phenomena remain to be addressed, which bear obvious characteristics to epigenetic. In the present study, using the expression of methylationrelated AtDML3 gene and methylation level of specific gene segments as end points, the methylation of cytosine, the most important feature of epigenetic, was investigated. It was shown that, in A. thaliana, rootloca lized αirradiation could induce epigenetic changes in aerial parts which avoided the direct irradiation. The radiation induced longrange epigenetic changes were confirmed in this study, which supplied innovative ideas for the further investigation of the mutagenetic mechanism of lowenergy ions irradiation.
由于低能离子较低的组织穿透能力, 其诱变机理一直是研究者争论的问题。 近年来, 本研究组的一系列研究工作已经证明在植物中存在辐射远程(诱变)效应, 从一个新的角度解释了低能离子的诱变机理, 然而依然无法解释低能离子辐照中的许多独特生物现象, 而这些现象均具有明显的表观遗传学特性。 以表观遗传学最具标志性特征的胞嘧啶甲基化为研究对象, 以α粒子拟南芥菜根辐照实验体系作为研究平台, 检测了远程组织(器官)甲基化相关基因 AtDML3 的表达及特定基因片段的甲基化水平。 研究证实, 在植物个体水平辐射可以诱导远程表观遗传的变化, 为进一步探索低能离子的诱变机理提供了新的思路。 Along the way, the mutagenic mechanism of lowenergy ions irradiation is a debatable issue. Recently, the existence of radiation induced longrange (mutagenic) effects in vivo in plants has been performed in a series of studies of our group, which account for the mutagenesis of lowenergy ions irradiation in a new perspective. However, numerous distinct biology phenomena remain to be addressed, which bear obvious characteristics to epigenetic. In the present study, using the expression of methylationrelated AtDML3 gene and methylation level of specific gene segments as end points, the methylation of cytosine, the most important feature of epigenetic, was investigated. It was shown that, in A. thaliana, rootloca lized αirradiation could induce epigenetic changes in aerial parts which avoided the direct irradiation. The radiation induced longrange epigenetic changes were confirmed in this study, which supplied innovative ideas for the further investigation of the mutagenetic mechanism of lowenergy ions irradiation.
2011, 28(4): 485-488.
doi: 10.11804/NuclPhysRev.28.04.485
摘要:
选用12C6+ 离子束对阿维链霉菌诱变选育高产菌株与原始菌株进行辐照诱变, 研究其累进辐照效应。实验结果表明,在辐照剂量为10 Gy时, 原始菌株比诱变高产菌株存活率高, 抗辐射能力强;辐照剂量高于30 Gy时,诱变高产菌株比原始菌株存活率高, 抗辐射能力强。原始菌株正突变率最高的辐照剂量为50 Gy, 致死率99.43%,正突变率最高, 达34.2%;对诱变高产菌株辐照剂量为30 Gy,致死率94.97%,正突变率最高, 达23.5% 。累进辐照效应降低了最佳辐照剂量。 Mutagenic effect on the mutant highproducing strain ZJAVY1203 and the original strain ZJAVA1 irradiated by ion beam of 12C6+ have been investigated. The experimental results indicated that the original strain has higher survival rate and stronger resistance to radiation than mutant highproducing Strain at dose of 10 Gy. The mutant highproducing strain has higher survival rate and stronger resistance to radiation than the original strain at the dose higher than 30 Gy. The lethality was 97% and the highest rate of orthomutation was 34.2%, when ZJAV A1 was irradiated by 50 Gy 12C6+ beam. The lethality was 94.97% and the highest rate of orthomutation was 23.5% when ZJAVY1203 was irradiated by 30 Gy 12C6+ beam. The best radiation dose is decreased by progressivity irradiation.
选用12C6+ 离子束对阿维链霉菌诱变选育高产菌株与原始菌株进行辐照诱变, 研究其累进辐照效应。实验结果表明,在辐照剂量为10 Gy时, 原始菌株比诱变高产菌株存活率高, 抗辐射能力强;辐照剂量高于30 Gy时,诱变高产菌株比原始菌株存活率高, 抗辐射能力强。原始菌株正突变率最高的辐照剂量为50 Gy, 致死率99.43%,正突变率最高, 达34.2%;对诱变高产菌株辐照剂量为30 Gy,致死率94.97%,正突变率最高, 达23.5% 。累进辐照效应降低了最佳辐照剂量。 Mutagenic effect on the mutant highproducing strain ZJAVY1203 and the original strain ZJAVA1 irradiated by ion beam of 12C6+ have been investigated. The experimental results indicated that the original strain has higher survival rate and stronger resistance to radiation than mutant highproducing Strain at dose of 10 Gy. The mutant highproducing strain has higher survival rate and stronger resistance to radiation than the original strain at the dose higher than 30 Gy. The lethality was 97% and the highest rate of orthomutation was 34.2%, when ZJAV A1 was irradiated by 50 Gy 12C6+ beam. The lethality was 94.97% and the highest rate of orthomutation was 23.5% when ZJAVY1203 was irradiated by 30 Gy 12C6+ beam. The best radiation dose is decreased by progressivity irradiation.
2011, 28(4): 489-497.
doi: 10.11804/NuclPhysRev.28.04.489
摘要:
基于球型光学模型、 预平衡发射和Hauser-Feshbach统计等理论, 编制了MENDF(Medium Energy Nuclear Data for Fission)程序, 该程序适用于裂变核在入射粒子能量低于200 MeV的中低能区的全套核数据计算。 对于中子和质子在200 MeV以下诱发的核反应, 其全截面、 反应截面、 弹性散射微分截面、 裂变截面和裂变中子谱、 5种发射粒子的单举截面和相应的能谱等理论计算值与相应的实验值基本符合。 MENDF在我国已被广泛用于核数据计算及建立中能核数据库。Based on the spherical optical model, preequilibrium and HauserFeshbach statistical theory, the code MENDF (Medium Energy Nuclear Data for Fission) is written to calculate a complete set of nuclear data for fission nuclei in the mediumlow energy region (≤200 MeV). For neutron and proton induced reactions below 200 MeV, the total cross sections, reaction cross sections, elastic scattering differential cross sections, fission cross section, energy spectra of fission neutron and five kinds of emitting particles, etc. are calculated by MENDF. The calculated data generally agree with their corresponding experimental data. MENDF is widely used for nuclear data calculation and to establish ENDF6 formatted files for the mediumlow energy region in China.
基于球型光学模型、 预平衡发射和Hauser-Feshbach统计等理论, 编制了MENDF(Medium Energy Nuclear Data for Fission)程序, 该程序适用于裂变核在入射粒子能量低于200 MeV的中低能区的全套核数据计算。 对于中子和质子在200 MeV以下诱发的核反应, 其全截面、 反应截面、 弹性散射微分截面、 裂变截面和裂变中子谱、 5种发射粒子的单举截面和相应的能谱等理论计算值与相应的实验值基本符合。 MENDF在我国已被广泛用于核数据计算及建立中能核数据库。Based on the spherical optical model, preequilibrium and HauserFeshbach statistical theory, the code MENDF (Medium Energy Nuclear Data for Fission) is written to calculate a complete set of nuclear data for fission nuclei in the mediumlow energy region (≤200 MeV). For neutron and proton induced reactions below 200 MeV, the total cross sections, reaction cross sections, elastic scattering differential cross sections, fission cross section, energy spectra of fission neutron and five kinds of emitting particles, etc. are calculated by MENDF. The calculated data generally agree with their corresponding experimental data. MENDF is widely used for nuclear data calculation and to establish ENDF6 formatted files for the mediumlow energy region in China.