2001 Vol. 25, No. 05
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The experiment of the 50m2 RPC carpet, carried out at Yang Ba Jing, Tibet, is studied using Monte Carlo simulation. The simulation can re-produce the non-uniform azimuth angle distribution shown in experiment data and reaches the conclusion that it is due to different reconstrucion errors in x and y directions on asymmetic carpet (8.6×6.1m2). Moreover, using the simulation data, the angular resolution and energy spectrum are given out.
Recently experiments found that multiplicities of final state particles in high energy reactions and their masses satisfy a simple universal experienced formula. In this paper the multiplicities of directly producted mesons and baryons in e+e－ annihilation and pp(p) reaction are calculated and are in complete agreement with the parameter in the experienced formula. And we can give a reasonable interpretation of parameters that are relevant to energy. The reasons of the mass universal relation are discussed.
An improved lattice Hamiltonian is applied to the SU(3) lattice gauge theory in 2+1 dimensions. The glueball masses of 0+ and 0－ have been calculated by using the coupled-clusters expansion with the truncated eigenvalue equations in a scheme preserving the continuum limit. The calculations up to third-order are carried out, and the results show better scaling behavior than that given by non-improved one.
By employing nonrelativistic and four-dimentional relativistic harmonic oscillator models, the effects of the interference cross section between tranverse and longitudinal photons on the nucleon spin structure function are calculated. Remarkable influence of this cross section in the resonance region provides more information for experiments to extract the spin structure function.
The in beam measurement of β+ delay α decay of 20Na on the Radioactive Ion Beam Line in Lanzhou(RIBLL) is reported. The radioactive ion 20Na was identified in beam by means of TOF-ΔE method. The implantation depth of the secondary beam in the detectors was optimized by a group of degraders with different thickness. The procedure of data acquisition was divided into two stages, i.e., in beam and off beam stage, to record the RIB and the β+ delay α particles respectively. Four resonant energy levels, 2.69, 3.09, 4.74, and 5.54MeV of 20Ne, have been observed with their relative amplitudes of 100, 4.15, 1.10 and 15.2, respectively. The half life of 20Na—→β+ 20Ne*→16O+α decay is preliminarily determined to be 459ms by using a time scaler combined with a pulse generator. The results are in good agreement with the ones of other group.
We have studied the fusion reaction for 11Be+208Pb near barrier by applying QMD model, and find taht in the fusion reaction induced by halo nuclei there simultaneously exist two mechanisms competing with each other. On one hand,11Be is a weakly bound nuclear system and is easily broke up caused by the interaction with target, when it approaches to target, so the fusion cross section is suppressed. On the other and, several neutrons of 11Be transfer into 208Pb and interact with 208Pb to cause the local radius of 208Pb increase and result in an enhancement of fusion cross section. The fusion cross sections calculatd show an enhancement near barrier, and the calculated results agree with the experimental data reasonably well.
The pure-neutron matter together with the neutron skin or halo in Ca isotopes is studied using the Skyrme-Hartree-Fock model. It is shown that the pure-neutron-matter thickness depends not only on the Fermi levels of the neutrons, but also on the orbital angular momentum of the valence neutrons. A new definition for the thickness of pure-neutron-matter is proposed. Particles in classically forbidden area are also studied. The number of neutrons in the classically forbidden area increases with mass number A, because of the increase in the number of neutrons occupied in the weaklybound open shell. The number of protons in the classically forbidden area, in contrast, decreases with mass number A, because the orbits of protons become more deeply bound. It is shown that the number of particles in the classically forbidden area can give information on the appearance of the halo or skin.
The squeeze out flow in the reactions of 124Sn+124Sn and 124Ba+124Ba at different energies for different impact parameters was investigated by means of isospin-dependent quantum molecular dynamics model. It was found that the more neutron rich system (124Sn+124Sn) exhibited weaker squeeze-out flow. This isospin dependence of the squeeze-out flow is shown to mainly result from the isospin dependence of nucleon nucleon cross section and the symmetry energy. Meanwhile, it is indicated that the squeeze-out flow depends strongly on the impact parameter and incident energy.
Within the framework of isospin-dependent Boltzmann-Langevin equation, the isotopic distribution in reaction systems of 14,16,18O+7,9Be at 28.7MeV/u were studied. It was found that the neutron rich (poor) nuclei were produced at the reaction of neutron rich(poor) projectile or target. The peak and width of the isotopic distribution shift toward the neutron rich side for neutron rich projectile. These shifts decrease with increasing the difference of proton numbers between the produced isotopes and the projectile.
The structure and pertormance of vertex chamber of BESⅡ are described. It covers 95%×4π of solid angle with the spatial resolution of σrφ≈100μm and σz≈2mm respectively.
Two important directions in the development of proton linacs are high-current proton linacs (mainly applied in nuclear power field) and compact proton linacs (for proton therapy). There are some common characteristics in them: 1. Employment of the novel accelerating structures, which are combination and evolution of the conventional ones; 2. Accelerating beam with small emittance; 3. Requirement for high reliability. The construction of the former is, however, much more difficult because it needs low beam lose rate and as high power transformation efficiency as possible. In this paper some important problems in the design of these accelerators are discussed and some schemes designed by us are presented.
The ion induced instabilities in the electron ring of the proposed Beijing τ-charm factory (BTCF) are studied. First, we calculated the length of the filling gap which can clear the ions produced in last turn, then simulated the process of the fast beam ion instability in BTCF and obtained its growth time, which is consistent with the theoretical prediction.
A new radioactive ion beam line designed to work at higher energy equivalent up to a magnetic rigidity of 10.64Tm is going to be constructed at Lanzhou. It is to connect the main ring and the experiment ring of the HIRFL-CSR complex. The separator is mirror symmetrically configured both in geometry and magnet strength, achieving a point point and parallel-parallel image at its intermediate focal plane with maximum spatial dispersion. Achromatism is automatically realized at the final focal plane. The total length is about 26 meters. Its resolution power of magnetic rigidity is 1200 at ±1% momentum deviation and ±25mrad divergence simultaneously. With sextupole-and octupole-magnets carefully positioned and powered, second and third-order aberrations are corrected to a large extent. The magnet design has already fulfilled.
The calibration of the energy response of the detection elements for soft X-ray spectrometer is reported. The calibration is carried out Beamline 3W1B of Beijing Synchrotron Radiation Facility with beam intensity 40—80mA at electron energy 2.2GeV,using vacuum chamber of reflectometer on An AXUV-100 silicon photodiode is used as the source intensity absolute monitor in the photo energy rang 150—1500eV. The energy response curves for X-ray diode (XRD) quantum efficiency,filter transmittance and grazing planar mirror reflection efficiency have been measured. Finally,the possible maximum errors of the XRD at different energies are given based on these experimental data.
A novel model for the inter-bunch interference in a bunch train is presented where a train of electron bunches passing through a bending or undulator magnetic field is considered as a moving multi slit diffraction array from which multi beams of coherent radiation emitted with definite phase difference. Based on this model,interference among multi-beams of coherent synchrotron radiation emitted from consecutive bunches accelerated by a 30 MeV RF-Linac at BFEL is analyzed and numerically calculated. From the discussions it is shown that: 1. Rapidly oscillating radiation enhancement due to inter-bunch interference is overlapped on the single bunch power spectrum;2. Such radiation enhancement consists of series of spectrum lines corresponding to harmonics of the fundamental of RF-Linac;3. Main maximum positions are determined by the “diffraction condition”;4. Intensity enhancement is about as high as the number of bunches in a macropulse;5. The axially measured radiation frequency is lower than the offaxis one. Experimental design to measure interference from separate bunches at the BFEL Linac with the developed mm-wave Michelson interferometer is presented.
Beijing Spectrometer (BES) at Beijing Electron Positron Collider (BEPC),IHEP has accumulated 2.5×107 J/ψ events and plans to increase this number to 108—109 in the near future. In this paper I review and summarize the recent studies on the possibilities of probing for new physics at BES. This includes the theoretical works on and experimental attempt performed at BES in searching for flavor changing neutral current,CP violation and lepton flavor violation in the processes of J/ψ decays.
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