2005 Vol. 29, No. 02
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the parameters of Ξ–n skyrme force are firstly determined according to the experimental data.With these parameters,the Ξ–potential depth,the single particle energy and the root mean square radius of Ξ–hyperon(hypernucleus)are calculated in the skyrme–hartree–fock framework.the results agree well with those of other models.
the gluon recombination functions in the twist–4 Qcd evolution equations are studied at the leading logarithmic approximation using both the covariant and noncovariant methods.We point out that the gluon recombination functions in the glr–mQ evolution equation are unavailable.the methods avoiding the ir divergences are discussed,which can be used in the derivations of the evolution kernels and coefficient functions at higher twist level.
using the improved hamiltonian of lattice gauge field and the truncated eigenvalue equation, we compute the glueball mass (mass gap) and glueball wave function of three–dimensional u(1) lattice gauge field. the result shows a good scaling behavior.
The Walecka model is extended to the neutron star matter, and in it's mean field approximation, the properties of neutron star matter consisted of proton, neutron and electron in uniform strong magnetic fields are studied. it is found that the ~equation of state (eos) becomes stiffer in some degree, and the ratio of neutron increase evidently while the one of proton and electron decrease with the magnetic field being stronger. the influence of the magnetic to the eos is smaller than the one to the fractions of the particles. the pressure of the neutron star matter is calculated by hydrodynamics and thermodynamics respectively. the stronger the magnetic field is, the more adjacent the curves of pressure depicted in these two ways are, and they are in superposition completely when the magnetic field is 1014T.
The relation of the 16N leak rate of the nuclear reactor to the efficiency and counting rate of γ–ray detector, velocity of high pressure vapor, is deduced. a conclusion of the efficiency independent on the velocity of high pressure vapor and decay constant of 16N is drawn. experimentally the space distribution of the relative efficiencies and the absolute efficiency at a refe~rence point are measured with Puc source emiting 6.13mev gamma ray detected by nai(tl) counter. The measured efficiency is consistent with monte carlo calculation in 7%. the compton small angle scattering contribution to the convergence length and the effect of the energy difference between 7.12mev and 6.13mev gamma ray on measured 16N leak rate are discussed.
high spin states in 134Ce nucleus have been studied by using the heavy–ion induced reaction 122Sn(16O,4n) carried out at china institute of atomic energy. the early level scheme has been extended with spin up to 22. however,our result is different from that in a recent publication,and the magnetic rotation bands reported there have not been confirmed. our observed level structures may be interpreted as shape coexistence. the 10+ state at the backbending with h11/2 quasineutron configuration has an oblate deformation with an asymmetry parameter γ≈–60°(lund convention),and the 10+ isomer is a yrast trap of prolate deformation with γ≈–120°,whereas the other signature partner bands with h11/2 and g7/2 proton configuration probably have a prolate deformation with γ≈0°.
The decay of bromine–76 was studied using compton–suppressed spectrometer and high–purity ge detectors in singles and coincidence mode, respectively. bromine–76 was produced via two reactions,i. e.,75As(α,3n)76Br and 76Se(p, n)76Br.the results of these experiments verified the previously reported levels and gammas of 76Se. in addition to the previously described transitions and levels, 39 new γ–rays and 15 new energy levels were found for the first time. spins and parities for new levels are proposed based on the calculated logft values, de–excitation modes of the observed states, and some nuclear reaction experiment results. a new decay scheme of 76Br is proposed in the present work. combining with the high–spin states observed by the in–beam γ–ray spectroscopy of a previous decay work, the positive–parity yrast states were compared with the results from calculations in the framework of the projected shell model.
Angular distributions of fragments b,c,n,o,f,ne,na,mg and al induced from the reaction of 19F+27Al have been measured at the beam incident energy of 114mev. the angular distributions and the element distributions at different angles were analyzed to provide an evolution process of the intermediate dinuclear system. the angular dispersion parameters were extracted from the experimental data and compared with the theoretical results. the dynamic dispersions for the dissipative products are not negligible and depend strongly on the charge number Z of the fragments,the deeper dissipation the more dynamic dispersion.
the ground state properties of the even–even nuclei with proton number Z=96—102 and neutron number N=162—190 have been systematically calculated in the deformed relativistic meanfield (rmf) theory with two sets of force parameters,tma and nl–Z2. We compare our results with those of the skyrme–hartree–fock model.the trends of the results for the two models are similar. the shell effect of the nuclei around N=184 is also discussed.
a tray of time of flight detector based on mrPc technology took part in the physics run of star both in p+p and d+au collisions in 2003. together with the information from the time Projection chamber(tPc) and the pseudo–vertex Position detector (pvPd) of the star experiment,corrections are done to calibrate the new prototype tof. the intrinsic time resolution of tofr reaches 85ps and it extends the π/K and K/p separation up to 1.6gev/c and 3.0gev/c respectively.
Time of flight counter (tof) is one of the main subdetectors of beijing spectrometerⅡ(besⅡ)for the identification of charged particles. due to the importance of particle identification in physics analysis,the measured time offset and resolution are carefully studied in this paper. using the hadron sample of j/ψ data,the variations of time offset and resolution versus pulse amplitued Q,coordinate z and βγ value are analyzed in detail. the correction functions of time offset and resolution are constructed respectively. finally,the results are checked from the hadron sample of ψ″ data when using the correction function.
Based on the detector and trigger simulation of beijing spectrometer Ⅲ (besⅢ), schemes of besⅢ emc triggers are studied. neutral triggers, bhabha triggers and charged event triggers are designed to fulfill the requirements of the physics goals. the trigger parameters are optimized and the ability of backgrounds rejection are carefully studied. trigger simulation for some typical physics channels are studied and the expected backgrounds event rates are obtained
We reported the muon beam test results of the first full–scale prototype of CMS RE1/2 Resistive Plate Chamber (RPC).The bakelite surface is treated using a special technology without oil to make it smooth enough.The full scale RE1/2 RPC with honeycomb supporting frame is strong and thin enough to be fitted to the limited space of CMS design for the inner forward RPC.The muon beam test was performed at CERN Gamma Irradiation Facility (GIF).The detection efficiency of this full scale RPC prototype is>95% even at very high irradiation background.the time resolution (less than 1.2 ns) and spatial resolution are satisfactory for the muon trigger device in future CMS experiments.The noise rate is also calculated and discussed.
A new CW electron accelerator with a single compact rf cavity, the rhodotron, has been applied widely in many fields of industrial irradiation. the paper focuses on dynamics characteristics of the rhodotron. the longitudinal and transverse dynamics simulations have been performed with the Parmela code. in this paper,synchronous condition of beam acceleration is deduced and the process of longitudinal phase capture is also studied.The problem that bulks overlap each other in the center of the RF cavity under the CW mode is solved by adjusting The parameters of bending magnets. the process that the major traverse focusing is achieved using the bending magnets is analyzed carefully.It is generalized how the space charge effect and the variation of initial parameters impact on transverse beam stability. the distribution of beam losing power is calculated for the radiation protection of this machine. the simulation results agree with The operational parameters of the Rhodotron's prototype, which confirm the research method's feasibility.
The phenomena that proton passes through the integer and half–integer resonance points in low energy proton circular accelerator with intense beams are discussed.The manufacturing tolerances of the dipole magnet and quadruple magnet is given through simulations on the cases when the injection energy is 1MeV and the accelerating RF voltage per one turn is 1kV and 2kV, respectively. With these given manufacturing tolerances, particles can safely cross over the integer and half–integer resonant points.
The three gradient method is a conventional means for beam emittance measurement. In intense electron beam accelerators,since the space charge effect is remarkable, the conventional three gradient method in not available.A MTGM(abbreviation for the Modified Three Gradient Method)is an improvement of the conventional three gradient method, the space charge effect is included in this method. In this paper, the basic theory of MTGM is stated, the principle of applying the MTGM method to beam diagnostics is described. Experiments are carried out on two electron beams of 3.5MeV, 2.6kA, 100ns and 18MeV,2.6kA 100ns separately, which scheme is presented. Results of these experiments are presented together with the error analysis. The results show that the MTGM method is an effective way of emittance measurement for intense pulse electron beam.
A mathematical model LET = cZdRb for identifying space heavy ions is established based on energy loss rate of the heavy ions in CR-39. Coefficients of the model are acquired through correlative curves between linear energy transfer and residual range. Another relation VT = A∙(REL) E<350B between etched rate of CR-39 and restricted linear energy transfer of the ions, which is experimentally found, is used to connect the mathematical model for getting an equation R = A0.0455 Z3.18VT-1. Finally, an identification formula Z3.18=64541.08+2.53 (dR/dVT-1) is obtained by means of calibration experiments.
Effects of low priming dose of radiation on cell cycle progression in hep G2 and Hela cells are investigated. For both cell lines, cells in the G2/M phase are accumulated temporarily after 5cGy γ-ray exposing, and the proliferation of tumor cells is significantly promoted by low dose radiation. When exposing to 3Gy γ-ray, only the G2 phase arrest occurred for hep G2 cells, and both S and G2 arrest occurred for HeLa cells. In contrast to treatment with high dose of radiation, when high dose was delivered 4hr after priming dose, pretreatment facilitates the accumulation of hep G2 cells in G2/M phase, however, pretreatment don’t significantly change the cell cycle progression of HeLa cells. It is concluded that alterations of the cell cycle progression by pretreatment with low dose of radiation are dependent on the type of tumor cell lines.
In this paper the electron axial channeling radiation has been compared with a free electron laser (FEL),and the possibility of reforming this type of radiation as γ–laser has been discussed.introducing equivalent magnetic field to describe ~electron’s motion,the pendulum equation and energy gain of the electron longitudial motion have been obtained using interaction of the electron with the radiation field. it shows that the channeling radiation is very similar to fel, if there exists standing wave field in the crystal.
the pentaquark has drawn great attention during the last two years in 2003 and 2004. this paper gives a relatively extensive review of the experimental and theoretical progress in the research of the pentaquark, including the contributions from several chinese groups. some open questions on pentaquark study are also discussed.
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