2001 Vol. 25, No. 8

Particle and field theory
Initial State Radiative Correction in R Measurement at BES
HU Hai-Ming, QI Xiang-Rong, HUANG Guang-Shun, ZHAO Zheng-Guo
2001, 25(8): 701-709.
Three typical schemes of the initial state radiative correction in e+e collision through single photon annihilation were reviewed, and the numerical results were calculated in the energy region of 2—5GeV. The differences of the theoretical values of radiative correction factors (1+δ) are about 1%—2%. The uncertainty of the effective (1+δobs) is estimated to be about 2%—3%.
Hadron Multiplicities and Its Momentum Spectra from Color Separate Connection among Final Partons in e+e Annihilation Events
SHAO Feng-Lan, XIE Qu-Bing
2001, 25(8): 710-719.
We calculate the hadron multiplicities and the momentum spectra of π±,K±,p/p in e+e→q+ng→hadrons for the case where the color separate singlet connections occur among the final partons q+ng with the help of JETSET event generator. We compare the results with those obtainted from the traditional color flow models and the available experimental data. The comparisons show that the momentum spectra obtained in the case of C-weight have a singnificant deviation from the data.,whereas those obtained in the case of T-weight are consistant with the data. The results from the case of T-weight are also consistant with those from the color flow model in most cases,and for proton, are even better than the later as implemented in default JETSET compared with the data.
Higher-Twist Effects on the Nucleon Spin Structure Functions in the Small Q2 Range
DONG Yu-Bing
2001, 25(8): 720-724.
Based on the quark model, the Q2 evolution of the nucleon spin structure functions in the small Q2 region is calculated. The higher-twist effects a2(Q2) and d2(Q2) are investigated. Comparison with other model calculations is also proceeded.
Nuclear and ion Physics
Level Structure in 209Fr
ZHOU Xiao-Hong, GUO Ying-Xiang, ZHU Shao-Fei, LEI Xiang-Guo, LIU Min-Liang, LIU Zhong, ZHANG Yu-Hu, HE Jian-Jun, ZHENG Yong, LUO Yi-Xiao
2001, 25(8): 725-730.
The high-spin states of 209Fr have been studied in the 197Au(16O,4n)209Fr reaction at 16O energies from 90 to 105 MeV using techniques of in-beam γ-ray spectroscopy. Measurements of γ-ray excitation functions,γ-γ-t coincidences and γ-ray angular distributions were performed with 4 BGO(AC)HPGe detecters. A level scheme for 209Fr with 21 γ rays was established for the first time,including a high-spin isomer with a measured half-life of (52±20)ns. Comparing with the low-lying level structure in 208Rn,it may conclude that the low-lying levels in 209Fr are formed by coupling the h9/2 proton to the neutron hole excitations in 208Rn. Thus,negative parities could be assigned tentatively to the low-lying states. The nucleus 209Fr,with four valence neutron holes and five valence protons outside the closed-shell nucleus 208Pb,also presents a competition between neutron-hole excitations and proton excitations in its low-lying level spectrum. Additionally,it should be pointed out that the higher-lying level structure in 209Fr does not follow the excitation pattern of 208Rn. We will pursue shell model calculations to interpret the level structure in 209Fr.
Measurement of β+ Delayed α Decay of 20Na
WANG Hong-Wei, WU He-Yu, JIN Gen-Ming, ZHANG Bao-Guo, XIAO Zhi-Gang, DUAN Li-Min, WEI Zhi-Yong, LI Zu-Yu, LU Zhao-Hui, LIU Yong-Ying, CHEN Ke-Liang, HU Rong-Jiang, ZHU Hai-Dong, CEN Ling, WANG Su-Fang, LI Xiang-Qing, CHEN Tao, HUA Hui
2001, 25(8): 731-735.
Through the 20Na β+ 20Ne→16O+α process,the half-life and β+ delayed α decay spectrum of 20Na have been measured on the Radioactive Ion Beam Line in Lanzhou(RIBLL). The 20Na was identified through TOF-ΔE method and alpha particle was measured by four Si(Au) surface barrier detectors. The half life of 20 Na is(459±7)ms. Result shows that in addition to nine high excitation energy levels with Ed≥2.688MeV, three low excitation energy levels of 20Na with Ed=0.890 & 1.054,1.991,2.424 & 2.457MeV were observed in the experiment. The relative intensity for 1.991MeV level, a more important energy level in the center of mass system energy region from 1.6 to 2.5MeV obtained in this experiment is much higher than the existed one. We also obtained the relative intensities of the levels of Ed=0.890 & 1.054,2.424 & 2.457MeV.
Quasiparticles Plus Rotor Model and the Analysisof Level Statistics of Odd-Odd Nucleus
CHENG Nan-Pu, ZHENG Ren-Rong, ZHU Shun-Quan
2001, 25(8): 736-742.
The energy levels of odd-odd nucleus 84Y at low spins were calculated by using the axially symmetric particles plus rotor model. In order to study the statistical properties of the energy levels, the two standard tests of Random-Matrix Theory such as the nearest-neighbor level spacings and the spectral rigidity were adopted. It is shown that the chaotic degree of the energy levels initially increases with increasing spin and reaches a maximum around I=10, and then decreases for spins above I≈10. On the other hand, the proton-neutron interaction makes the energy levels slightly regular/ordered. However, the Coriolis force which makes the energy levels chaotic plays a major role in the spectral structure of the odd-odd nucleus 84Y.
Study about Light Hypernuclei and YN Interaction Based on Chiral SU(3) Quark Model
ZHANG Miao-Jing, SHEN Peng-Nian, LIU Xian-Hui, KONG Fan-Xin
2001, 25(8): 743-753.
In terms of the YN interaction based on the chiral SU(3) quark model,the spectra of light hypernuclei 4ΛH,4ΛHe and 5ΛHe are calculated. The result shows that the effective local ΛN potential,as an approximation,cannot offer a reasonable explanation of the empirical data, while the non-local ΛN potential,also as an approximation,can provide a reasonable range of the binding energy of 5ΛHe and correct ordering of the energy levers of 4ΛH,4ΛHe. This indicates that the non-local character of the effective YN interaction plays an important role in binding behavior. The upper bounds and lower bounds of energy levels are given by employing two sets of model parameters in the calculation. Thus,the experimental data of hypernuclei can provide more information as the constraints of model. In the present stage,YN interaction(no matter phenomenology of theoretical interaction) cannot be finalized due to lack of experimental data. Utilizing experimental data,it is possible to optimize model parameters in the theoretical studies of YN interaction.
Odd-Even Difference of Moment of Inertia of NuclearSuperdeformed States in A~190 Region
GUO Jian-You, XU Fu-Xin, RUAN Tu-Nan
2001, 25(8): 754-758.
By fitting the E2 transition spectra of superdeformed bands in A~190 region, the coefficients of Bohr-Mottelson's I(I+1) expansion are determined and moments of inertia of band head are calculated out. All results show that the moments of inertia of odd-A nuclei are systematically larger than those of the neighboring even-even nuclei, and the moments of inertia of odd-odd nuclei are systematically larger than those of the neighboring odd-A nuclei. The odd-even difference of moment of inertia of nuclear superdeformed states is obvious.
Density Dependence of Proton Fraction in Neutron Stars
LI Wen-Fei, 2< sup>, ZHANG Feng-Shou, CHEN Lie-Wen
2001, 25(8): 759-764.
Within the framework of Skyrme-Hartree-Fock theory based on the extended Skyrme effective interaction, the proton fraction in β-stable neutron stars was investigated for the charge neutrality condition. The density dependence of symmetry energy strength coefficient was studied with different potential parameters, and the behavior of proton fraction in neutron stars at high density for these potential parameters was obtained. The calculated results show that the proton fraction disappears at high density for potential parameters SII, SIII and SKM, which implies that the pure neutron matter may exist in the interior of neutron stars. It is also found that adding muons in neutron stars will increase the proton fraction.
Entrance Channel Dependence of the Isospin Effects of the Nuclear Stopping in Intermediate Energy Heavy Ion Collisions
YANG Yan-Fang, LIU Jian-Ye, ZUO Wei, GUO Wen-Jun, ZHAO Qiang
2001, 25(8): 765-771.
The entrance channel dependence on the isospin effects of the nuclear stopping in intermediate energy heavy ion collisions was studied by using the isospin-dependent quantum molecular dynamics with three forms of the symmetry potential. It shows that the nuclear stopping is sensitive to the beam energy, the impact parameter and the mass of the colliding system, especially very sensitive to the isospin dependence of in-medium nucleon-nucleon cross section, but insensitive to the symmetry potentials and the ratio of neutron to proton of colliding system. From this investigation, we propose that nuclear stopping can be used as a new probe to extract information on the isospin dependence of in-medium nucleon-nucleon cross section in intermediate energy heavy ion collisions.
Bremsstrahlung Radiative Correction in QED at Finite Temperature
2001, 25(8): 772-779.
Based fully on the finite temperature field theory, we calculate the Feynman diagram to analyse the new infrared divergence caused by the temperature effect in the bremsstrahlung process. It turns out that both of the infrared divergence at the zero and finite temperature can be cancelled by the identical Feynman diagram of virtual processes. We derive the probability of radiating a net energy ω in bremsstrahlung processes and the result in Eikonal approximation is the same as that obtained in the semi-classical approximation.
Beam-Beam Study in Beijing Electron Positron Collider mini-β Scheme
WANG Sheng, FANG Shou-Xian, ZHANG Chuang
2001, 25(8): 780-786.
For performing mini-β scheme in the Beijing Electron-Positron Collider (BEPC),high RF voltage is supplied for shortening the bunch length,but results in the luminosity decrease. This is the special phenomenon of beam-beam on BEPC, which limits the performance of mini-β scheme. The work is aiming to explain the special phenomenon and overcome it. The conclusion of theoretic analysis,simulation and machine study is that,for BEPC,the bunch length influences the beam-beam interaction mainly through the “hourglass”effect and a veraging over the betatron phase during the collision, and these two contrary effects make the luminosity to be maximum only when σsy (the ratio of bunch length and beta function of y-direction) is near the optimal value, and so the luminosity decrease due to high RF voltage can be avoided.
Design of a New DC-RF Injector Used in High Average Power FEL
HU Yan-Le, ZHAO Kui, CHEN Jia-Er, ZHANG Bao-Cheng, HAO Jian-Kui, WANG Li-Fang
2001, 25(8): 787-792.
Here we give the design proposal of a new DC-RF injector used in high average power FEL. The injector includes a Pierce gun and a 1+1/2 SC cavity. It will be able to provide high average beam current because it can work in CW mode. By changing the shape of the first 1/2 cell of SC cavity to enforce the focusing effect, we can decrease the distance between photocathode and SC cavity. Thus, the growth of emittance can be suppressed effectively. Through the simulation of particle dynamics with PARMELA, the shape of Pierce gun and the optimized synchronous phase of the SC cavity can be decided. The simulation results show that this kind of injector is feasible.
Synchrotron radiation,applications of nuclear techniquees,etc
A Proton Beam Delivery System for Conformal Therapyand Intensity Modulated Therapy
YU Qing-Chang, KE Xue-Yao
2001, 25(8): 793-798.
A scattering proton beam delivery system for conformal therapy and intensity modulated therapy is described. The beam is laterally spread out by a dual-ring doublescattering system and collimated by a program-controlled multileaf collimator and patientspecific fixed collimators. The proton range is adjusted and modulated by a programcontrolled binary filter and ridge filters.