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Study of the structure of unstable nuclei through the reaction experiments

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Science china(physics,Mechanics & Astronomy) 2011年第S1期54卷 1-5页

作者： CAO ZhongXin & YE YanLin state key laboratory of nuclear physics and technology, school of physics, peking university, beijing 100871, china 1. state key laboratory of nuclear physics and technology School of Physics Peking University Beijing 100871 China

Along with the development of the radioactive nuclear beam facility, the study of the structure of unstable nuclei has progressed rapidly over the last few decades. Due to the weakly binding property, the structure information of the unstable nuclei comes primarily from the scattering or reaction experiments. Therefore it would be very important to understand clearly the reaction mechanism involved in the experiment. We outlined here the major reaction mechanisms which are adequate to the study of unstable nuclei, with the focus on the new phenomena and methods in comparison with those with traditional stable nucleus beam. Especially emphasized are the breakup and knockout reactions, developed as accurate tools for spectroscopy investigation into the nuclear structure with low intensity secondary beam. Couplings of the breakup channel to the elastic scattering and the fusion and transfer reactions are also reviewed.

关键词： binaries: unstable nuclei nuclear structure breakup reaction knockout reaction fusion reaction transfer reaction

X-ray flares of γ-ray bursts: Quakes of solid quark stars?

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Science china(physics,Mechanics & Astronomy) 2009年第2期52卷 315-320页

作者： XU RenXin1 & LIANG EnWei2 1 school of physics and state key laboratory of nuclear physics and technology, peking university, beijing 100871, china 2 Department of physics, Guangxi university, Nanning 530004, china 1. school of physics and state key laboratory of nuclear physics and technology Peking University Beijing 100871 China 2. Department of physics Guangxi University Nanning 530004 China

A star-quake model is proposed to understand X-ray flares of both long and short γ-ray bursts (GRBs) in a solid quark star regime. Two kinds of central engines for GRBs are available if pulsar-like stars are actually (solid) quark stars, i.e., the SNE-type GRBs and the SGR-type GRBs. It is found that a quark star could be solidified about 103 to 106 s later after its birth if the critical temperature of phase transi- tion is a few Metga-electron-volts, and then a new source of free energy (i.e., elastic and gravitational ones, rather than rotational or magnetic energy) could be possible to power GRB X-ray flares.

关键词： γ-rays bursts: X-rays neutron stars elementary particles

Recent HERMES Results on DVCS from Proton and nuclear Targets

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原子核物理评论 2009年第S1期26卷 124-128页

作者： YE Hong-xue,MAO Ya-jun (school of physics and state key laboratory of nuclear physics and technology,peking university,beijing 100871,china) school of physics and state key laboratory of nuclear physics and technology Peking UniversityBeijing 100871China

Spin structure is one of the fundamental subjects in the study of nucleon structure. Recently it is found that Generalized Parton Distributions(GPDs) are related to the total angular momentum carried by partons,which offers a possible solution to the spin puzzle in the first time. We get access to certain GPDs by looking at the azimuthal angle asymmetries attributed to the interference between Deeply Virtual Compton Scattering(DVCS) and Bethe-Heilter processes in HERMES experiment. By measuring the asymmetry with respect to transverse target polarization from proton target,a model-dependent constraint on Ju vs Jd is obtained. Another worldwide unique channel is nuclear DVCS. The preliminary results on asymmetries with respect to beam spin and beam charge are reported.

关键词： GPDs DVCS TTSA nuclear DVCS

Kinetic characteristics of continuous flow polymerase chain reaction chip: A numerical investigation

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Science china(Technological Sciences) 2010年第7期53卷 1967-1972页

作者： WANG ShiYing1 & WANG Wei2,3 1 school of physics, peking university, beijing 100871, china 2 Institute of Microelectronics, peking university, beijing 100871, china 3 National key laboratory of Science and technology on Micro/Nano Fabrication, beijing 100871, china 1. school of physics Peking University Beijing 100871 China2. Institute of Microelectronics Peking University Beijing 100871 China3. National Key Laboratory of Science and Technology on Micro/Nano Fabrication Beijing 100871 China

Continuous flow PCR (polymerase chain reaction) chip holds impressive advantages compared to micro chamber PCR chip. In order to have better understanding of kinetic characteristics of continuous flow PCR chip, a comprehensive mathematical model is presented in this paper, including melting, annealing and extension phases of a typical PCR process which has the essence of a convection-diffusion-reaction system. Using this model, we can simulate the PCR process in series of reaction cycles. Numerical results show that the average sample velocity plays a significant role in affecting the amplification efficiency. Also, appropriate combination of the PCR mixture is important for high-quality DNA amplification. Giving a large initial DNA concentration range, the continuous flow PCR scheme holds excellent real-time detection ability theoretically. The present numerical model bridges the temperature distribution to the real DNA amplification, and thereby is able to successfully predict continuous flow PCR properties which are important for the chip design.

关键词： continuous flow PCR chip numerical simulation convection-diffusion-reaction system

Magnetic moments of ^(33)Mg in the time-odd relativistic mean field approach

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Science china(physics,Mechanics & Astronomy) 2009年第10期52卷 1586-1592页

作者： LI Jian1,ZHANG Ying1,YAO JiangMing1 & MENG Jie1,2 1 school of physics,state key laboratory of nuclear physics and technology,peking university,beijing 100871,china 2 school of physics and nuclear Energy Engineering,Beihang university,beijing 100191,china school of physics State Key Laboratory of Nuclear Physics and Technology Peking University Beijing 100871 China school of physics and nuclear Energy Engineering Beihang University Beijing 100191 China

The configuration-fixed deformation constrained relativistic mean field approach with time-odd component has been applied to investigate the ground state properties of 33Mg with effective interaction *** ground state of 33Mg has been found to be prolate deformed,β2=0.23,with the odd neutron in 1/2[330] orbital and the energy -251.85 MeV which is close to the data -252.06 *** magnetic moment -0.9134 μN is obtained with the effective electromagnetic current which well reproduces the data -0.7456 μN self-consistently without introducing any *** energy splittings of time reversal conjugate states,the neutron current,the energy contribution from the nuclear magnetic potential,and the effect of core polarization are discussed in detail.

关键词： magnetic moment binding energy time-odd component configuration-fixed deformation constrained calculation relativistic mean field theory

β-decay studies of the neutron-rich ^(18,21)N isotopes

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Science china(physics,Mechanics & Astronomy) 2011年第S1期54卷 53-60页

作者： HUA Hui, LI ZhiHuan, YE YanLin, JIANG DongXing, LOU JianLing, LI XiangQing & XU FuRong school of physics and state key laboratory of nuclear physics and technology, peking university, beijing 100871, china 1. school of physics and state key laboratory of nuclear physics and technology Peking University Beijing 100871 China

The β-decay studies of neutron-rich 18,21N isotopes have been performed using β-n, β-γ, and β-n-γ coincidence methods. The 18,21N ions were produced by the fragmentation of the 22Ne and 26Mg beams, respectively, on a thick beryllium target. The time of flight of the emitted neutrons following the β-decay of 18,21N was measured by a neutron detector system with wide energy detection range and low-energy detection threshold. In addition, several clover germanium detectors were used to detect the β-delayed γ-rays. The half-lives of the β-decays of 18N and 21N were determined to be (619±2) ms and (82.9±7.5) ms, respec tively. Several new β-delayed neutron groups were observed with a total branching ratio of (6.98±1.46)% and (90.5±4.2)% for 18N and 21N, respectively. The level schemes of 18O and 21O were deduced. The experimental Gamow-Teller β-decay strengths of 18N and 21N to these levels were compared with the shell model calculations.

关键词： β-delayed neutron decay 18 21N neutron detector system branching ratio Gamow-Teller strength

Simulation of g factor for size optimization and coupling in phased array coil design

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Progress in Natural Science:Materials International 2006年第2期16卷 120-124页

作者： SONG Xiaoyu, ZHANG Hongjie, WANG Le, BAO Shanglian, SUN Yanrong and ZU Donglin (beijing key laboratory of Medical physics & Engineering, peking university, beijing 100871, china physics school, peking university, beijing 100871, china) [a]beijing key Labaratory of Medical physics & Engineering Peking University Beijing China [b]physics school Peking University Beijing China

The effect of geometric parameters of the coil element in an array on signal-to-notse ratio (SNR) and g factor of parallel imaging are analyzed, and the optimal parameters for the maximal SNR and minimal g factor are also given in this paper. In addition, the effects of coupling on SNR and g factor have been analyzed. The test results indicate that g factor for parallel imaging is greatly increased and SNR is decreased for coupling. According to the optimization, a six-channel parallel coil has been designed for torso imaging.

关键词： MRI phased array coil SENSE parallel imaging.

Near-field properties of a shell nanocylinder pair with gain materials

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Chinese physics B 2012年第11期21卷 388-392页

作者：王乔吴世法王晓钢 MOE key laboratory of Materials Modification by Beams School of Physics&Optoelectronic EngineeringDalian University of Technology state key laboratory of nuclear physics and technology School of PhysicsPeking University

We study the near-field response of a shell nanocylinder pair, with its core filled by gain materials, using a two- dimensional finite-difference time-domain method. It is shown that the gain materials in the core of the cylinder can compensate for the intrinsic absorption of the metal shell, leading to local-field enhancement in the gap of the active pair. A linear dependence is found between the field enhancement and the gain coefficient at resonance. The detailed physics is studied by calculating the electrical-field distribution of the shell pair filled with different gain materials. The influence of the gap width and the shell thickness on the interaction of two adjacent active shell cylinders is also investigated.

关键词： shell nanocylinder pair gain material local-field enhancement

Design of an MRI quadrature-data acquisition card

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Progress in Natural Science:Materials International 2006年第3期16卷 255-259页

作者： JIANG Zhongde, ZU Donglin and GU Xiaofang (Institute of Heavy Ion physics, beijing key laboratory of Medical physics & Engineering, school of physics, peking university,beijing 100871, china) [a]Institute of Heavy Ion physics Beijing Key Laboratory of Medical Physics & Engineering School of Physics Peking University Beijing China

A design of a quadrature-data acquisition card based on peripheral component interconnect (PCI) bus for mini-type magnetic resonance imaging (MRI) system is reported. It uses two high speed analog-to-digital converters (ADCs) to sample the MRI signals and two static random access memories (SRAMs) to store the data which will be read to the computer by PCI bus after sampling. All the logic control signals on the card are generated by the field programmable gate array (FPGA). The software Foundation3.1 is used to design the FPGA and achieve useful result after simulating and implementing. The card has some merits that normal commercial cards do not have. For example, the sampling parameters can be varied according to different pulse sequences.

关键词： MRI data acquisition FPGA PCI bus.