2002 Vol. 26, No. 12
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High spin states of 125Sb have been investigated for the first time by means of in-beam γ-ray spectroscopy techniques via the 124Sn(7Li, α2n) reaction at 32 MeV beam energy. Based on the measurements of γ-γ coincidence and γ-ray anisotropies, a level scheme including 21 new γ-transitions and 14 new excited levels was established up to 23/2+. Three isomers at 1970, 2110 and 2471 keV levels have been identified and proposed as three-quasiparticle πg7/2ν(h11/2s1/2), πg7/2ν(h11/2d3/2) and πg7/2ν(h211/2) configurations, respectively. The level structure of 125Sb is ?discussed in terms of particle-core coupling
It is of great interest to build a high luminosity accelerator in τ-charm energy region. The physics interest in this energy region is briefly reviewed. Events rate and events number at different energy in one year's data taking are estimated under typical luminosity of 1033cm－2s－1. It is pointed out that the luminosity of a newly designed accelerator should be optimized between ψ″and ψ(4160), the peak luminosity should be determined by the events rate which the trigger system, detector electronics and data acquisition system could handle.
We study a flavor-changing toppion production process e+e-→tcΠ0t in the topcolorassisted technicolor(TC2) model. The studies show that, with high centre of mass energy in TESLA collider, the production cross section of e+e-→tcΠ0t is about 0.1 fb in most parameter regions of TC2 model and a few tens events of toppion can be produced each year. The resonance effect can enhance the cross section to a few fb when toppion mass is small. With clean background, the toppion events can possibly be detected at TESLA collider. On the other hand, we find that there exists a narrow peak in the toppion-charm invariant mass distribution which could be clearly detected. Therefore, the toppion production process e+e-→tcΠ0t provides a unique chance to detect toppion events and test the TC2 model.
Based on the phase-space generating functional for a system with a singular higher-order Lagrangian,the quantal canonical Noether identities under the local and non-local transformation in phase space for such system have been derived. For a gauge-invariant system with a higher-order Lagrangian,the quantal Noether identities under the local and non-local transformation in configuration space have also been derived. It has been pointed out that in certain cases the quantal Noether identities may be converted to the conservation laws at the quantum level. This algorithm to derive the quantal conservation laws is significantly different from the first quantal Noether theorem. The applications to the non-Abelian CS theories with higher-order derivatives are given. The conserved quantities at the quantum level for some local and non-local transformation are found respectively.
The new experimental data of 11B(p,α1)8Be*(1)(2α) three-body decay show that the continuous α spectrum of the two alpha particles produced by the intermediate nuclear 8Be*(1) looks like a saddle type distribution. To explain the experimental facts, we have written a Monte Carlo simulation program to the p+11B reaction. The calculation results of the program indicate that the anisotropy distribution emission of the decay alpha particles produced by 8Be*(1) can give a satisfying explanation to the experimental spectrum.
Exact eigen-energies and the corresponding wavefunctions of the interacting sl-boson system in U(2l+1) transitional region are obtained by using an algebraic Bethe ansatz with the infinite dimensional Lie algebraic technique. Numerical algorithm for solving the Bethe ansatz equations by using mathematica package is also outlined.
Within the isospin dependent Brueckner-Hartree-Fock approach,the equation of state of isospin asymmetric nuclear matter and its isospin dependence have been investigated in the whole isospin range. The present work has been focused on the effects of a microscopic three-body force on the equation of state of asymmetric nuclear matter and nuclear symmetry energy. It is shown that,even with the presence of the three-body force,the empirical parabolic law of the energy per nucleon vs isospin asymmetry is still fulfilled accurately in the whole isospin range (0≤ β ≤1). Around the empirical saturation density ρ0=0.17fm－3,the three-body force effect on the symmetry energy is rather small and the symmetry energy at the saturation density obtained in the presence of the three-body force is 30.71MeV in good agreement with its empirical value 30±4MeV;while at high density,the three-body force provides a strong enhancement of the symmetry energy and makes the symmetry energy increase much more rapid as increasing density. A simple parametrization of the symmetry energy as a function of density is proposed
The mass and charge distribution of residual products produced in the spallation reactions needs to be studied,because it can provide useful information for the disposal of nuclear waste and residual radioactivity generated by the spallation neutron target system. In present work,the Many Stage Dynamical Model(MSDM) is based on the Cascade-Exciton Model (CEM) We use it to investigate the mass distribution of Nb,Au and Pb proton-induced reactions in energy range from 100 MeV to 3 GeV. The agreement between the MSDM simulations and the measured data is good in this energy range,and deviations mainly show up in the mass range of 90—150 for the high energy proton incident upon Au and Pb.
Using the hypothesis as well as the γ-ray strength function proposed by us, the neutron radiative capture reaction cross sections and the γ energy spectra have been calculated for 93Nb,natural Ag and 181Ta in the neutron incident energy region from 0.01 to 5MeV as well as for 197Au in the neutron incident energy region from 0.01 to 10MeV. The results which are coincident better with the experimental values were obtained. The comparisons with the experimental values have shown that, not only the abnormal protuberances near and after 5.5MeV of the γ spectra in the nuclear mass regions about 110<A<140 and 180<A<210 are explained better,but also the γ production data can be theoretically calculated for the middle and heavy nuclei by means of this hypothesis and the γ-ray strength function deduced from this hypothesis.
Effects of the symmetry potential Usym and the isospin dependence of in-medium nucleon-nucleon cross section Nn( Np) on the number of neutron (proton) emitted as well as their dependence on the momentum dependent interaction (MDI) are studied within an isospin dependent Quantum Molecular Dynamics (IQMD) model. The isospin dependence nucleon-nucleon cross section is found to have a much stronger influence on the Nn( Np) especially for the neutron-deficient collision system with MDI in the energy region from about 100 to 400MeV/nucleon. The calculation results are clear to show that the number of neutron (proton) emitted during reaction in the neutron-deficient system,depends sensitively on the isospin dependence of in-medium nucleon-nucleon cross section and weakly on the symmetry potential with MDI. In this case one can make use of the number of neutron (proton) emitted as a probe to extract simultaneously both the magnitude and the in-medium nucleon-nucleon cross section.
Using a hadron and string cascade model,JPCIAE,and the corresponding Monte Carlo events generator,the behavior of the charged particle ratio event-by-event fluctuations in subsystem depending on energy,centrality,resonance decay and rapidity interval was investigated for Pb+Pb collisions at SPS and ALICE energies,and for Au+Au collisions at RHIC energies. The model results of charged particle ratio event-by-event fluctuations as a function of the rapidity interval in Pb+Pb collisions at SPS energies were comparable with the preliminary NA49 data. It turned out that the charged particle ratio fluctuation has no strong energy,centrality,resonance decay and rapidity interval dependences.
The non-uniform longitudinal flow model (NUFM) proposed recently is extended to include also the transverse flow. The resulting longitudinally non-uniform collective expansion model (NUCEM) is applied to the calculation of rapidity distribution of kaons, lambdas and protons in relativistic heavy ion collisions at CERN-SPS energies. The model results are compared with the 200A GeV/c S-S and 158 A GeV/c Pb-Pb collision data. The central dips observed in experiments are reproduced in a natural way. ;It is found that the depth of the central dip depends on the magnitude of the parameter e and the mass of produced particles, i.e. the non-uniformity of the longitudinal flow which is described by the parameter e determines the depth of the central dip for produced particles. Comparing with one-dimensional non-uniform longitudinal flow model, the rapidity distribution of lighter strange particle kaon also shows a dip due to the effect of transverse flow.
A two-dimension position sensitive parallel-plate avalanche (PPAC) detector has been developed for RIBLL. The detector consists of one anode and two cathodes. In each cathode a resistance chain is used to readout position signals. The detector has been tested in different operating gases with an α source. When the detector is at 7mb flowing rate of isobutane and +500V on anode, the position resolution of 0.76mm is obtained. For 7mb C3F8 and +595V on anode, the position resolution is 0.64mm. The efficiencies are around 99.1% in the cases of C3F8 and isobutane.
The efficiencies of clover and cluster composite detectors using NaI and BGO crystals as the media for detection of high energy γ ray are systematically simulated with Monte Carlo method. It is shown that for the same geometry of detection media concerned the efficiency of the composite BGO detector is much higher than that of the composite NaI detector. Therefore NaI crystal is not a suitable medium of composite detectors for high energy γ ray duo to low efficiency, Doppler broadening and distortion to γ spectrum in comparison with BGO crystal. The composite BGO detectors have many advantages such as large photopeak efficiency, small Doppler effect and regular γ spectrum. As to the clover and cluster composite detectors consisting of the cylinders of BGO crystal with original size 76×127, the intrinsic photopeak efficiencies are over 40% and the enhanced factor of absolute efficiencies is as high as 2.4 and 2.7, respectively, for 22 MeV γ ray.
Small cell drift chamber is adopted in the design of BESⅢ-the upgrade version of the BES detector, for its lower electron diffusion and better spatial resolution. We did Monte Carlo study for BES-Ⅲ drift chamber using GARFIELD7, and got the characteristics of the output signals of the sense wires. This become the theoretical basis for the design of drift chamber readout electronics.
To have a high positron yield,it is extremely important to minimize the primary electron beam radius at the positron production target. Various effects on electron beam blow-up have been analyzed.By comparing the measured beam radius with simulation,result at current BEPC positron source,some concrete effects on beam blow-up have been described. A design study on minimizing the electron beam radius at BEPC-Ⅱ positron source is given,and the ways to reach this goal have been summarized.
We propose to build a GeV γ-ray beam line, Shanghai laser Electron Gamma Source-Ⅱ (SLEGS-Ⅱ), at the Shanghai Synchrotron Radiation Facility (SSRF). By Backward Compton Scattering (BCS) of ultraviolet laser from 3.5 GeV electrons of SSRF, high intense quasi-monochromatic BCS γ-rays with high linear or circular polarization ranging 300-870MeV will be produced. In this paper, we present the outline of SLEGS-Ⅱ and the properties of BCS γ-ray with numerical computation based on the major parameters of SSRF storage ring. The selection of interaction region and tagging position is discussed.
The identical graphite targets were irradiated by 60keV Ni+and Ar+ ions with the fluences of 1018/cm2 in turns under the same experimental conditions. Using high-resolution transmission electron microscope (HRTEM) with energy dispersive X-ray (EDX) and electron diffraction (ED), we found different-size nanoscale Ar-bubbles embedded in glass-carbon-like membranes for the first time. Moreover, in part of these nanobubbles Ar may have been formed into a solid-like structures.
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