2004 Vol. 28, No. 6
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An introduction for ηc physics research is presented in this paper, which shows that the meachnism of ηc decays can't be well described by current theoretical models and detailed experimental measurements need to be done with larger ηc sample. Based on the expected J/ψ and ψ′events taken with the planed BESⅢ detector in one year, the ηc physics researches are discussed extensively, including the measurements of branching fractions of different final states, the search for new decay modes, precision measurements of mass and width, and the search for rare decays. At last, the study of η′c decays is also discussed briefly.
We consider the contributions of the physical top-pions predicted by topcolorassisted technicolor (TC2) models to the single top production via the t-channel process eq→et at the HERA and THERA colliders. We find that the neutral top-pion can generate large contributions to the process ec→et. In most of the parameter space, the production cross section is in the range of 1—6pb. The signals of the neutral top-pion can be studied in the HERA and THERA colliders.
The coupled cluster method is improved with the random phase approximation (RPA) to calculate the glueball mass in the 2+1-D SU(2) lattice gauge theory. In this calculating, the trial wave function consists of single-hollow graphs, the Feymann-Hellman theorem is used to obtain a set of closed equations. When the calculation proceeds up to the sixth order, the calculated results of glueball mass show scaling window and a sign of converges at weak coupling region 1/g 2>1 0. The results of this paper indicate that the seventh order glueball mass will show good scaling behavior and the converges.
High-spin states in 179Pt have been studied experimentally using the 149Sm(35Cl, p4n) fusion-evaporation reaction at beam energies of 164—180MeV. Measurements of γ-ray excitation function, X-γ coincidences and γ-γ-t coincidences were carried out with 13 BGO(AC) HPGe and 3 LOAX detectors. Based on the measured results, three rotational bands built on intrinsic states assigned to the 1/2－, 5/2－ and 7/2+ Nilsson configurations have been established for 179Pt. It has been observed that the aligned angular moment in the 1/2－ band increases suddenly around hω=0.27MeV. The big signature splitting has been observed in the 7/2+ band. These phenomena are discussed by referring to the systematics of the level structure in the Pt isotopes and isotones of 179Pt.
Several methods for calculating absolute γ-ray intensities and their uncertainties are introduced briefly. Some factors which affect the uncertainties of absolute γ-ray intensities are discussed in detail. The problem about “error double counting” and “Iγ=100” are discussed for the first time. As an example the application is also given through nuclear decay processes.
In the framework of the constituent quark model, the spin-orbit splitting of the lowest L=1 excited states of N and Λ are analyzed by using various quark potential models. The results show that only when a two gluon exchange phenomenological flavor dependent l·s term is considered in the potential, the spin-orbit splitting of N and two sets of Λ L=1 states can be explained simultaneously.
Using modified surface delta interaction, the deformed Hartree-Fock calculations for twenty two nuclei such as 102—114Ru, 102—116Pd,104—116Cd etc. are performed in the gds and gdsh configuration space, respectively. Prolate and oblate configurations are obtained. It is shown that there exist shape transitions for the nuclei with the mass number from 102 to 116, the resultant single-particle energy spectrum is changed not only with the mass number but also with the configuration, and the results, by considering the 1h11/2 orbit, are quite different from those obtained in the gds configuration space. Moreover, the number of protons in the nucleus and filling up the 1h11/2 orbit, especially with neutrons, play important roles in the single-particle energy spectrum and the shape transition.
The liquid-gas phase transition in the heavy ion collisions and nuclear matter has been an important topic and got achievements, such as, based on the studies by H. Q. Song et al the critical temperature of liquid-gas phase transition enhances with increasing the mass of system and reduces as the increase of the neutron proton ratio of system. As we know that both the liquid-gas phase transition and the isospin fractionation occur in the spinodal instability region at the nuclear density below the normal nuclear density. In particular, these two dynamical processes lead to the separation of nuclear matter into the liquid phase and gas phase. In this case to compare their dynamical behaviors is interested. We investigate the dependence of isospin fractionation degree on the mass and neutron proton ratio of system by using the isospin dependent quantum molecular dynamics model. We found that the degree of isospin fractionation (N/Z)n/(N/Z)imf decreases with increasing the mass of the system. This is just similar to the enhance of the critical temperature of liquid-gas phase transition T c as the increase of system mass. Because the enhance of T c is not favorable for the liquid-gas transition taking place, which reduces the isospin fractionation process and leads to decrease of (N/Z)n/(N/Z)imf. However the degree of isospin fractionation enhances with increasing the neutron proton ratio of the system. It is just corresponding to the reduce of Tc of the liquid-gas phase transition as the increase of the isospin fractionation of the system. Because the reduce of Tc enhances the liquid-gas phase transition process and also prompts the isospin fractionation process leading the increase of the isospin fractionation degree. To sum up, there are very similar dynamical behaviors for the degree of isospin fractionation and the critical temperature of the liquid-gas phase transition. So dynamical properties of the liquid-gas phase transition can be measured and studied through the studies of isospin fractionation experimentally.
The influence of angular momentum in the context of isospin effects on the emission of different light particles for heavy fissioning isotopic sources of 189,202,212Po and for isobaric sources of 202Fr,202Po and 202Tl is studied within the framework of the Smoluchowski equation. Calculations show that the isospin effects on particle emission have a strong dependence on the angular momentum. Large angular momentum greatly weakens the influence of nuclear dissipation and isospin on particle emission. This means that to better extract dissipation strength with light particle multiplicities as a probe, it is important to select the compound systems with low spins, in addition to selecting a proper kind of particles for the systems with different isospins.
Starting from the Schwinger-Dyson equation for the photon propagator in QED, we derive a useful relation between the Debye mass and the thermodynamic pressure. Using this relation, we calculate the two-loop Debye mass from relevant pressures at finite temperature and chemical potential. The result indicates that the two-loop correction decreases the Debye screening mass. We also discuss the magnetic mass in QED plasma.
A multi-variable particle identification method is developed for the BESⅡ physics analysis. Besides the traditionally used TOF-T and dE/dx information, TOF-Q and BSC-E are also used to improve the particle discrimination ability. It is shown that the particle identification efficiency, misidentification probability and systematic error could be improved with this new method. The multi-variable method can be extended to even more variables, and can be used in other experiments.
SiC films were deposited on Si substrates by RF co-sputtering of the Si and C compound target and implanted by 120keV N ions. The structure, optical property of thin films were studied by Fourier transform infrared spectrum(FTIR) and photoluminescence(PL) spectroscopy. The obtained results suggested that carbon nitride single, double and triple bonds are formed in the N ions implanted SiC films, and the luminescence intensity depends strongly on the quantity of N ions.
The old file management system for BES offline calibration is reviewed. A new method of using database to manage BES offline calibration constant data is presented, and its whole implementation in Linux is described in detail. The feasibility, advantages and further improvements are also discussed.
In this paper, the structure and performance of the Si-PIN detector system are introduced. The neutron sensitivity of the proton recoil Si-PIN detector to 14 MeV neutron is analyzed. Meanwhile, the direct irradiation sensitivity is simulated by MCNP-4B program. Using the Si-PIN detector, the pulsed neutron yield from DPF device has been measured. The results are in accordance with the SDIN500 detector within 5% uncertainty.
The general features of the first in-vacuum wiggler designed and constructed in Beijing Electron Positron Collider (BEPC) as a part of the BSRF upgrade project are introduced. The measured magnetic field of the in-vacuum wiggler reaches 2.0 Tesla when operated at the gap of 12mm, which will provide high flux in the hard X-ray region and will be mainly used for the high temperature and high pressure diffraction experiments. The key technologies and difficulties for the magnetic and mechanical design of the in-vacuum wiggler are described. The main parameters and the requirements for the in-vacuum wiggler are given too. Also, the magnetic field measurement results are shown.
Detailed research has been done on the aspects of the design of a Halbach structure permanent hexapole, such as the permanent material adoption, the structure design, and the dimension selection and etc. A possible method has been proposed to solve the problem of demagnetization in some magnetic blocks. By optimizing the geometry structure, the magnetic field in the working aperture is made to be the maximum for a certain condition. Some useful codes like POISSON, PERMAG, and TOSCA are used to simulate the sextuple magnetic field. Some useful plots are also presented.
The electron cloud effect limits the performance of several accelerators with high beam current, such as SLAC and KEK B factories, the CERN SPS and the CERN PS. In this paper, the electron trapping in general 2n multipole magnet (n is integer) is studied, and we find that there exists electron trapping in the adiabatic region of the multiple magnet (n>1).
The high current and short bunch of the electron beam in the BEPCII injector linac cause the wakefield effects on the beam performance dilution. These wakefield effects on longitudinal and transverse beam dynamics are systematically studied with analysis and numerical beam modeling, including the single bunch short-range wake effects and the multi-bunch long-range wake effects on beam energy, energy spread, emittance, orbit offset and primary electron beam spot size on the positron production target. The measures to effectively cure these wake effects are also studied.
An additional beam with opposite charge state is added into the dynamic simulation of the t-Code program PARMTEQ. The space charge effect and multi-bunch effect during the positive and negative ion beams acceleration are considered. The result is given for a four-vane type RFQ accelerator. The purpose of simulation is focused on the investigation of possible dynamic problems caused by two-beam acceleration in RFQ structure. Two-beam acceleration is prior to diminish the transverse space charge effect, but “trap” between opposite charge state ions in longitudinal position appears when the beam current is large, which is the main cause of the increasing number of longitudinal loss. Therefore new RFQ structures should be designed specially for two-beam acceleration to obtain higher transmission rate than single beam acceleration.
Considering the effect of photoelectron, BEPCⅡ′s beam position monitor (BPM) uses antechamber structure. The cut-off frequency of TE mode is maybe lower than the BPM signal processing frequency 500MHz. The power of TE mode will result in beam position measurement error. With monitoring the antechamber's TE mode power amplitude and calculating the transmission of TE mode power to BPM's electrodes, we can calculate the error of position measurement caused by TE mode. We found that the error is beyond the acceptance when the cut-off frequency of TE10 mode is lower than 500MHz. By changing the slot length, the cut-off frequency is higher than 500MHz and the error could be accepted. At last the effect of the wakefield to the beam has been simulated and the longitudinal impedance of wakefield has been calculated.
Single mesh size phantoms are usually used in the calculations of BNCT dose rate by Monte Carlo method, such as 4mm, 8mm, 16mm. The result with 16mm mesh size model simulations produce unacceptable accuracies. Although the 4mm model simulation has a good precision, it costs lots of memories and computation time. The mixed mesh size model has the same precision as 4mm model, but its computation time is only 37% of that.
The enstenite and its melt inclusions picked up from mantle xenoliths at Longgang volcanoes in Jilin province are measured by synchrotron radiation X-ray microprobe techniques. Some element contents, such as K,Sc,Ti,Cr,Mn,Fe,Co,Ni,Cu,Zn,Ga,Sr,Y are calibrated by NIST SRM 612. The relative deviations of element contents analyzed in enstenit between X-ray fluorescence microprobe and wavelength dispersive electron beam microprobe are 15%,5%,7% and 8% for Cr,Mn,Fe,Ni,respectively. Chondrite normalized transition metal elements distribution pattern of inclusion is similar to that of whole rock analyzed by INAA, which implies that primitive magma experienced partial melting or segregation during ascending.
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