2006 Vol. 30, No. 1
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Provided the enhancement in the pp spectrum in radiative decay J/ψ→γpp observed by the BES collaboration is due to an existence of a pp molecular state, we calculate its binding energy and lifetime in the linear σ model. Concretely, we consider a possibility that the enhancement is due to a pp resonance which is in either S-wave or P-wave structure and compare our results with the data. Moreover, pp can annihilate at s-channel which is absent in deuteron, thus by studying the total width of the pp bound state, we may gain more information about the linear σ model and some concerned issues
Using observation data of the Yangbajing extensive air shower array from October 2000 to September 2001, the TeV gamma rays from the shell-like SNR G40.5-0.5 direction were detected. A region with the highest excess of 4.4σ was found using two dimensional analysis method.The position of EGRET unidentified source GeV J1907+0557 is near the centrer of the region.
The excitation functions of elastic scattering proton which were measured with inverse kinematics of elastic resonance scattering reactions in GANIL and MSU have been fitted by the multi-energy level $R$-matrix theory. The final result shows that the new energy levels order for nucleus 11N should be 1/2+,1/2－,5/2+,3/2+, 3/2－,5/2+,7/2－,which is consistent with the experimental results of 11Be (the mirror nucleus of 11N) and the theoretical calculation of 11N with GCM theory.
Angular distributions for elastic transfer in the 6He+9Be system were measured at the incident 6He laboratory energy of E=150MeV. From a distorted-wave Born approximation (DWBA) analysis,3He spectroscopic amplitude in 9Be were extracted and compared with values obtained by shell model calculations. The result shows that the spectroscopic amplitude is much greater than 0.70.
Based on the Improved Quantum Molecular Dynamics Model the fusion reactions of 40,48Ca+90,96Zr are studied by making a more rigorous treatment of the initial condition. The study shows that:(1) the calculated fusion cross sections for all four reactions of 40,48Ca+90,96Zr are in good agreement with experiment data; (2) the sub-barrier fusion for the neutron-rich reaction 40Ca+96Zr is ubstantially enhanced as compared with the other three reactions. In order to understand the reason why the sub-barrier fusion of the neutron-rich reaction 40Ca+96Zr is enhanced as compared with the non-neutron-rich reaction 40Ca+96Zr and that of the neutron-rich reaction 48Ca+96Zr is not enhanced, the further investigations are carried out, those are: the dynamic fusion barriers for four reactions, the relation between dynamic fusion barrier and nucleon transfer and the relation between nucleon transfer and corresponding reaction Q value. It has been found that positive Q value leads to the strong nucleon transfer which reduces the dynamic fusion barrier and enhances the sub-barrier fusion cross section.
Based on the macroscopic liquid drop model and microscopic model with the modified single-particle oscillator potential, we have systematically calculated the ground state properties of superheavy even-even nuclei with proton number Z=94—112. The theoretical binding energies and alpha-decay energies are in good agreement with the experimental data. They also agree well with Moller's theoretical results. The reliability of macroscopic-microscopic model when it is used in superheavy nuclei is confirmed by our calculation and comparison. The properties of some unknown nuclei are predicted and they will be useful for future experimental research.
The ground state properties of the four isotope chains, 28Ni,54Xe,78Pt,94Pu are studied in the relativistic mean-field theory by using two sets of parameters, NL-3 and NL-Z. We find that the binding energies of odd-A nuclei are even closer to the corresponding experimental results, compared with those of the even-even nuclei. Our results indicate that it is reliable to neglect the space component of the vector meson fields in calculating binding energies of odd-A nuclei in the relativistic mean-field theory.
The two-pion correlation functions are different for some pion source distributions in two-pion interferometry.If quark-gluon plasma of cylindrical shape is produced in relativistic heavy ion collisions, the pion mesons will emit from the surface of quark-gluon plasma of cylindrical shape and the corresponding correlation function will have a special oscillation behavior. The oscillation behavior can be used to verify the existence of quark-gluon plasma and is also a signature of the appearance of quark-gluon plasma.
Alpha decay half-lives of even-even superheavy elements are calculated in the framework of the effective liquid drop model using the combination of constant asymmetry shape description for the mass transfer and the effective inertia coefficient.We have tested this model in the range of Z=88—98 at first.Then we extend this model to the superheavy area of Z≥100. The comparisons between calculated half-lives and experimental data show that the effective liquid drop model is very efficient to describe the alpha decay process of even-even superheavy elements.
The development and production of 400 sets of T9 type TGC (Thin Gap Chamber) for ATLAS experiment are undertaken by Shandong University. In this paper, the process of development of T9 type TGC is introduced first and then the method of measuring the detection efficiency of the TGC is described. The testing result of detection efficiency of 288 sets of T9 type TGC built by Shandong University shows that all the detectors excellently fulfill the quality requirements of ATLAS experiment.
With the construction of the new Radioactive Ion Beam Line in Lanzhou (RIBLLⅡ) which connects the CSRm and the CSRe, an experimental setup for physics research is highly required. A large area neutron detection wall is the main part of the setup. This paper introduced the detection principle of the neutron detection wall and the Monte-Carlo simulation of its design under the environment of the Geant4 toolkit. We presented the final design with the optimized parameters and the performance of the wall.
The converging part of electron accelerator is designed to converge the phase of injecting electrons, improving the beam quality of the accelerator. It is very crucial to calculate the coupling factor between cavities and to design the geometry structure of the coupling irises. By the E module of code MAFIA, we calculate the frequency of every single resonant cavity and the two eigenfrequencies of two-cavitiy line. Then we get the coupling factor between the two cavities.This method can be used to design the geometry structure of the coupling irises between every two cavities. Compared to experiment, the results of the method is very accurate.
BEPCⅡ— an upgrade project of the Beijing Electron Positron Collider (BEPC) is a factory type of e＋e－ collider. The fundamental requirements for its injector linac are the beam energy of 1.89GeV for on-energy injection and a 40mA positron beam current at the linac end with a low beam emittance of 1.6μm and a low energy spread of ±0.5% so as to guarantee a higher injection rate (≥50mA/min) to the storage ring. Since the positron flux is proportional to the primary electron beam power on the target, we will increase the electron gun current from 4A to 10A by using a new electron gun system and increase the primary electron energy from 120MeV to 240MeV. The positron source itself is an extremely important system for producing more positrons, including a positron converter target chamber, a 12kA flux modulator, the 7m focusing module with DC power supplies and the support. The new positron production linac from the electron gun to the positron source has been installed into the tunnel. In what follows, we will emphasize the positron source design, manufacture and tests.
The mechanism of electron emission from ferroelectric cathode is introduced.Distribution of the applied static field in ferroelectric cathodes is simulated by MAFIA codes. It is shown that the structure of front electrode can obviously influence the static field at the triple-point of ferroelectric cathode.A ferroelectric cathode with isolated electrodes can attain stronger multiplicative field at the triple-point, which may be helpful in getting efficient and stable electron emission. In the recent experiments, we have already got stable electron emission over 100A from a PLZT8/65/35 cathode with isolated electrodes.
Due to the solar modulation and other factors, the cosmic ray flux has some changes which maybe induce variation of the Earth's climate, such as cloudiness. It is possibly an effective way to research connection between cosmic ray and cloud through studying effect on cloudiness of galactic cosmic ray flux associated with Forbush decrease (FD) events, because climate variation, especially cloudiness, has a response to the FD events.Three FD events had been recorded with Yangbajing neutron monitor during the years from 2003---2004. Variation of cloudiness following FD over the regions of Yangbajing cosmic ray observation has also been observed by infrared radiometer. By statistically analyzing the FD events, it has been found that significant increase of cloud takes place during FD events. The results indicate that the cloudiness increases at lower latitudes in the regions of thinner cloud, which is consistent with results at this lower latitudes found by other investigators.
The two in-circuit test systems, one is a HP4156 semiconductor parameter automation system for measuring steady total dose effect, another one is a system for measuring pulsed total dose effect, under different environment with working principle and technical specification are introduced in detail in the paper. The comparison study of total dose damage effects irradiated by Pulsed hard X ray and long pulsed γ-ray generated in Qiangguang-Ⅰaccelerator, and by 60Co steady γ-ray on typical CMOS devices utilizing the two test systems has been performed, which lays a foundation for the further research of total dose effect on CMOS devices in the future.
Doppler-broadening slow positron annihilation spectroscopy is used to measure the concentration, spatial distribution, and size of open-volume defects in surface and interface of material. In this method, the quantitative evaluation is generally carried out with the line shape parameter S and W, but sometimes the parameters provide some finite information. For example, if positron and electron form positronium (include o-Ps and p-Ps) in material, the parameters S and W may provide little information about positronium even complicate the analyses. A parameter I3γ, defined as o-Ps self-decay intensity, was used to analyze Ag layer capped and non-capped silica aerogel by slow positron annihilation Doppler -broadening spectroscopy. The result shows that I3γ can provide more information for researching mesoporous material and nanometer film.
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