2006 Vol. 30, No. 2

Particle and field theory
New Soliton Solutions in Noncommutative Torus
WEN Jun-Qing, ZHU Qiao, SHI Kang-Ji
2006, 30(2): 89-93.
Besed on finite dimensional reduced matrices of operators on integral noncommutative torus, soliton solution problem can be converted into the finite matrix solution problem satisfying the algebraic equation Q(M)=0. In this paper, we mainly study the condition of reduced matrix for the operator which cannot be diagonalized. When the potential function V(\phi)=0 has an extremum point in three or more rank, there exist matrix solution that cannot be diagonalized for the finite dimensional matrix equation V′(M)=0$. We study the general form of the solution and construct new soliton solution on noncommutative integral ring. In terms of the construction method, we obtain soliton solutions on noncommutative orbifold.
Nuclear and ion Physics
Model-independent Statistical Analyses of High-Multiplicity and Larger-fluctuation data in Different Energy-Ranges
LAN Xun, QIAN Wan-Yan, CAI Xu
2006, 30(2): 94-98.
High-multiplicity and large-fluctuation data for nucleus-nucleus collision processes at different energy-ranges are analyzed in an event-by-event manner, by using model-independent statistical methods. The result of the analyses obtained by using CERN-EMU01(32S on fixed Au target at 200A GeV) data and that obtained by using RHIC-STAR(Au+Au at \sqrt{s_{_{\rm NN}}}=200GeV) data are compared with each other; they are also compared with the existing result obtained by using JACEE-data at cosmic-ray energies. The results of such comparison are presented and discussed.
Study of Quasiparticles Bands in Odd-Odd 188Au
FANG Yong-De, ZHANG Yu-Hu, ZHOU Xiao-Hong
2006, 30(2): 99-104.
High-spin level structure of 188Au has been studied via the 173Yb(19F, 4nγ) reaction using techniques of in-beam γ-ray spectroscopy. Based on the experimental results, the level scheme of 188Au has been revised significantly. The previously reported positive parity levels have been modified and a new 20+ level was proposed to feed the 18+ states via two low-energy transitions. The existence of the 20+ and the level structures above it are similar to those in the neighboring odd-odd 190,192Au,therefore, the π h_{11/2}^{-1}\otimes \upnu i_{13/2}^{-2} h_{9/2}^{-1} configuration was assigned to the 20+ state.
Near-barrier quasi-elastic cross sections and barrier distribution of 32S+90,96Zr
WU Xiu-Kun, LIN Cheng-Jian, YANG Feng, LIU Zu-Hua, ZHANG Huan-Qiao, ZHANG Chun-Lei, ZHOU Ping
2006, 30(2): 105-107.
Quasi-elastic cross sections have been measured for 32S+90,96Zr with high accuracy near the Coulomb barrier at backward angles and the barrier distributions are extracted from them. We find that barrier distribution of 32S+96Zr is flat and extends to low energies. The sub-barrier fusion cross sections are strongly enhanced because of such barrier distribution. Compared with the reaction of 32S+90Zr, 32S+96Zr has stronger neutron transfers up to the six-neutron pickup, which is due to the positive Q values of neutron transfers in the latter. This indicates that the neutron transfer may play a role in the enhancement of sub-barrier fusion for 32S+96Zr.
Non-Reproducibility of the Cross Sections of the Products Induced from Dissipative Reaction of 17F+27Al
HAN Jian-Long, WANG Qi, DONG Yu-Chuan, LI Song-Lin, DUAN Li-Min, WU He-Yu, XU Hua-Gen, CHEN Ruo-Fu, XU Hu-Shan, BAI Zhen, LI Zhi-Chang, LU Xiu-Qin, ZHAO Kui
2006, 30(2): 108-112.
The differential cross sections of the dissipative products B, C, N, O, F, Ne, Na and Mg induced from the reactions of 19F+27Al at two incident energies have been measured at the HI-13 tandem accelerator, Beijing. In the case of a fixed beam incident energy 114MeV or 118.75MeV respectively, identical reaction system and the same detection system, 20 target points in steps of 2mm on a 10mm×50mm rectangular Al foil have been bombarded. The experimental results indicate that the probability distribution of the cross sections is much wider than a standard Gaussian distribution. This non-reproducibility of the cross sections can't be interpreted by the statistical property of a finite count rate.
Calculations of α-Decay Half-Lives by the Generalized Viola-Seaborg Formula
DONG Tie-Kuang, REN Zhong-Zhou
2006, 30(2): 113-117.
The Viola-Seaborg formula is a well-known formula for α decay half-life of heavy nuclei. In this work we obtain a set of new parameters for this formula through a least-square fit to even-even nuclei between Z= 84 and Z=110 with N greater than 126. On average, the formula can reproduce the half-lives of heavy even-even nuclei with a factor of 1.3. In order to improve the calculated results for odd-A nuclei and for odd-odd nuclei, we obtain a generalized form of the Viola-Seaborg formula by including the influence of orbital angular momentum of α particle on half-lives of odd-A nuclei and odd-odd nuclei. On average, half-lives of odd-A and odd-odd nuclei can be reproduced with a factor of 2.5 by the generalized Viola-Seaborg formula.
Thermal Property of Protoneutron Star Matter
2006, 30(2): 118-122.
We study the composition, the temperature and the equation of state of isoentropic protoneutron star matter in the mean field approximation of the relativistic σ-ω-ρ model.It is shown that, fixing the baryon density, the fraction of neutron at S=2 is smaller than that at S=1 and the fractions of proton, electron, and muon at S=2 are larger than those at S=1, respectively, especially in the region of low baryon density. Keeping baryon density invariant, the fractions of hyperons at S=2 are larger(smaller) than those at S=1 in the region of relative low(high) density of baryons. Also the temperature, the energy density and the pressure at S=2 are larger than those at S=1, respectively. In addition, we demonstrate that the finite entropy impose more influence on the fractions of particles as well as the temperature than on the equation of state of the protoneutron star matter. As a consequence, the contributions of antiparticles are very small under our consideration.
Critical Behavior of Multifragmentation in Finite Nuclei and Extraction of Critical Exponents
HUANG Xi, ZHANG Feng-Shou, FENG Zhao-Qing, JIN Gen-Ming
2006, 30(2): 123-127.
Using a phenomenological asymmetric nuclear equation of state, we obtained pressure-density isotherms of the finite nucleus 112Sn simulated in r-space and in p-space and constructed the nuclear fragments by using the coalescence model. After correlatively analysing the fragments, the signal of critical behavior has been found and critical exponents were also extracted.
Low-Lying Spectra and Electromagnetic Transition Rates in 140—162Gd in the Interacting Boson Model
LU Li-Jun, ZHANG Jin-Fu
2006, 30(2): 128-133.
Spectra and electromagnetic transition for the even-even 140—162Gd isotopes are studied in the framework of the interacting boson model. A schematic Hamiltonian can be used to describe their spectra and transition. The results show that 140—162Gd are in the transition from the vibrational limit to rotational limit.
Chaotic Motion of Single Particle in the Potential of Nonaxial Octupole Deformation
JIN Hua, ZHENG Ren-Rong, ZHU Shun-Quan, LI Jun-Qing
2006, 30(2): 134-139.
The single particle's chaotic motion in the potential of a prolate harmonic oscillator plus Y32+Y3-2 non-axial octupole deformation was systematically analyzed from the classical and quantum-mechanical viewpoint. The classical trajectory stability analysis showed that the characteristics of the potential surface would be important for the particle's motion. By investigating the phenomena of avoided level crossing in the system and the evolution of the coherent initial state, it is found that the non-axial feature of octupole deformation potential can make the single particle to go to chaos easier.
Detection Technology and Methods
Further Corroboration of Equivalence of Two χ2 Forms
MO Xiao-Hu
2006, 30(2): 140-146.
The equivalence of two χ2 forms for linear function fit is proved.The two forms of χ2 are applied on a simplified R-value measurement to test the equivalence.
Multipactor Experiment on a Micro-pulse Electron Gun
ZHAI Ji-Yuan, TANG Chuan-Xiang, ZHENG Shu-Xin, LI Quan-Feng
2006, 30(2): 147-150.
The micro-pulse electron gun (MPG) is a new type of cold cathode microwave electron gun that can produce short duration, high current density electron beam. The principle of MPG is multipactor (or multipacting). In this paper, our proof-of-principle experiment on a MPG is presented. One kind of Cu-Al-Mg alloy has been used as the cold cathode. A current with the density up to 100mA/cm2 was observed. The results agree well with the analytical calculation and the computer simulation. The experiment verifies both the analytical theory and the computer code, and prepares the way for the higher current density approach.
PAD Design for the Phasing System of BEPCⅡ Linac
GEN Zhe-Qiao, HOU Mi, PEI Guo-Xi
2006, 30(2): 151-154.
Phase and amplitude measurement is one of the most important issues for the phasing system of BEPCⅡ linac. Two kinds of PAD, based on analog and digital I/Q demodulator respectively, have been constructed and tested in both laboratory and the klystron gallery of BEPCⅡ linac. A calibration algorithm based on LMS method is used to compensate the mismatches of the analog I/Q demodulator. Experiments show that both kinds of PAD run stably and can meet the requirements of the phasing system.
Microwave System for BEPCⅡ-Linac
ZHAO Feng-Li, HOU Mi, ZHAO Yan-Ping, LIU Jin-Tong, ZHANG Jing-Ru, ZHOU Yao-Xiang, HAN Da-Wei
2006, 30(2): 155-158.
Specifications of microwave system for BEPCⅡ-Linac were enhanced by a wide margin in comparison with those of the microwave system for BEPC-Linac. For this reason many RF components must be developed and improved. This paper introduces the developments of SLED detuning system, accelerating section, high power waveguide valve, high power dummy-load, and medium & high power waveguide attenuator/phase shifters. High power operation of the microwave system has been carried out.
Construction and Commissioning of HLS Injection Bump System
SHANG Lei, WANG Xiang-Qi, WANG Lin, JIA Dao-Man, ZHAO Feng
2006, 30(2): 159-162.
This paper describes the construction and the commissioning of the new injection bump system of HLS ring. An emphasis of the discussion is put on various errors of the system and the method of evaluation and reduction. After some improvements and fine adjustment, an average injection rate of 2—6mA/s was obtained in the daily operation and a maximum accumulated current of 400mA achieved. The injection system has run for almost two years and played an important role in the operation of the light source.
The Experiments of Transverse Feedback System on the BEPC
YUE Jun-Hui, MA Li, CAO Jian-She, ZHANG Lei
2006, 30(2): 163-165.
In order to cure the transverse coupled-bunch instabilities of BEPCⅡ and improve the beam current of the rings, a prototype of transverse bunch-by-bunch feedback system was studied and made. The experiment of this prototype on the BEPC storage ring shows that this system can work well. The beam instabilities can be successfully suppressed when the feedback loop is closed. This paper describes the prototype of the transverse feedback system and the preliminary test results.
Synchrotron radiation,applications of nuclear techniquees,etc
Design of a Pulsed Low Energy Positron System Based on Beijing Intense Slow Positron Beam
MA Yan-Yun, PEI Shi-Lun, CAO Xing-Zhong, WANG Ping, WEI Cun-Feng, MA Chuang-Xing, ZHANG Zhi-Ming, WANG Shu-Hong, WANG Bao-Yi, WEI Long
2006, 30(2): 166-170.
The design of a pulsing system for an intense slow positron beam is described in this paper. Slow positron annihilation lifetime measurement is an important method to study the depth-dependent characteristics of the surface and near surface. The start signal for slow positron lifetime measurement can be obtained from the pulsing system, which consists of a reflection type chopper, a prebuncher and a buncher. On the basis of the simulation of dynamics process by Parmela, the frequency of the buncher and the positron energy have been chosen to be 150MHz and 330eV respectively. The designed time resolution of this system is about 150ps (FWHM).
Optimized Voxel Model Construction and Simulation Research in BNCT
LI Gang, DENG Li
2006, 30(2): 171-177.
The voxel model of Snyder head phantom is widely used in simulation of BNCT. This paper introduces a simplified method which is based upon only four kinds of materials. The new voxel model keeps the mass conservation when the mesh size is small such as 4mm. The 4-material voxel model and 286-material voxel model with different mesh sizes of 16mm, 8mm, 4mm, are simulated respectively by MCNP Monte Carlo code. The results indicate that the 4-material voxel model can reach good accuracy. Using this method, multi-voxels are produced and simulated. Compared to the 4mm single voxel model, the multi-voxel model has good accuracy and less computational time. Finally, we recommend multi-voxel models and a reasonable number of meshes. Its computational time and accuracy have accessed the clinical BNCT requirement.
Beam Hardening Correction Base on Monte Carlo Simulation Method
ZENG Gang, YU Zong-Qiang, YAN Yong-Lian
2006, 30(2): 178-182.
For the empirical beam hardening correction in computerized tomography (CT), it is necessary to measure an attenuation curve for the material. The attenuation curve depends on the X ray machine operation parameters and object material, etc. If any measuring condition changes, a new attenuation curve has to be measured. This approach is time consuming and difficult to implement. A new method of beam hardening correction is presented in this paper, which is based on Monte Carlo simulation of the attenuation characteristic. An aluminium object is scanned and the projection data is corrected by the empirical beam hardening correction and by the simulation based correction. The results of the reconstructed images confirm the correctness of the simulation based method. The simulation based correction has been applied successfully to CT projection data of several test samples, with the material of aluminum, steel and copper.