1999 Vol. 23, No. 5
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The distribution properties of the total fission kinehc energy and of the mass of fission fragments at different initial excitation energies of hot nuclei in the reaction 25MeV/u 40Ar+209Bi are investigated. The initial excitation energies are obtained according to the linear momentum transfer. The experimental results show that the fission kinetic energy distribution is similar to the case of compound nuclei with lower excitation energy when the initial excitation energy of hot nuclei is below 380MeV. While the inihal excitation energy is above 380MeV, the most probable value of fission kinehc energy increases with the inihal excitahon energy. The fission energy spectra become asymmetric due to an enhancement of the yield at higher kinetic energies, and the width of mass distribution increases rapidly.
We introduced the stngture, installation and the first step experimental resultS of the 50m2 in YBJ. Our conclusion is that RPC can work very well in YBJ where the altitude is 4000m a.s.l and the pressure is 594 mbar.
By using the diagonal solution of reflection equation for A(n－1)(1), IRF model, We obtain the solution with n+1 parametcrs to the reflection equation of Zn Belavin model. The result we get when n=2 coincides formally with that given by Hou et al.
By using the transforming operators, the Q-deformation of the nonharmonic oscillator algebra is obtained. Based on the algebra, the Q-deformation of generalized coherent states are introduced. It is found that these states have the overcompleteness and they are the minimal uncehainty states for the Q-deformed natural operators, and the relative rate of squeezing of the Q-deformation of generalized even coherent state increases with the degree of deformation in the principal squeezing region.
The event generator of quark combination model is obtained by replacing LUND string fragmentation model in JETSET7.3. Then this generator is applied to study the e+e－→h′s process. Using much less adjustable parameters than other models. It is found that quark combination model can reproduce a lot of data, such as the average hadron mulhplicities, the difference &bl betWeen b-quark and light-quark events, the baryon to meson ratios, the event shape distributions and the baryon antibaryon correlations, etc. The reason for some of its predictions deviated from data is discussed. Moreover, it is found that quark combination model can give more direct understanding for some phenomena, eg., the baryon to meson ratios and the baryon antibaryon correlations, etc.
We proposed a new method to determine the in-medium QMC parameters consistently. Our resultS illustrate that the bag constant and the nucleon radius are greatly influenced by the nuclear medium, however, the parameter for zero-point motion keeps its vacuum value. Then we discuss the effects of in-medium QMC parameters on the equation of state of nuclear matter and quark condensation in nuclear maser.
Within the framework of an isospin-dependent quantum molecular dynamics model, the balance energy has been calculated for reaction systems 58Fe+58Fe and 58Ni+58Ni at different impact parameters. It is shown that the balance energy of the neutron-rich system 58Fe+58Fe is higher than that of the system 58Ni+58Ni, which could be in qualitative agreement with the results of the experiments.
The isotope distribution produced by the intermediate energy heavy ion reactions of induced by different projectiles have been calculated based on statistical abrasion model in which new inmedium nucleon-nucleon collision cross section and diffuseness of nuclear matter distribution are used. The effect of the medium and the diffuseness of the nuclear matter distribution has been investigated.
The QCD-like gauged NJL model with flavors Nf=2 is developed to derive the gap equation for the fermion in nuclear medium. In the free space, the gluon part in the gauged NJL model may contribute nearly 1/4 to the fermion mass. The chiral order parameter is consistent closely with the prediction of the QCD sum rules. Based on the gap equation, the fermion mass in nuclear medium is obtained and the dynamical properties of the scalar and pseudoscalar mesons are studied. The numerical results in the free space are in fair agreement with the experimental data.
The proposed hadron and string cascade model, JPCIAE, for ultrarelativistic nucleus-nucleus collisions based on the LUND model and the PYTHIA event generator especially, is used to inveshgate the J/ψ suppression due to the nuclear absorption of a J/ψ in minimum bias pA and BA collisions at 200A GeV energy. With the different sets of reasonable formation bine for hadron and J/ψ the results of J/ψ suppression factor from both the usual scenario and the Glauber-like simulations are comparable with all the NA38 PA and BA data, except the NA50 data of Ph+Pb collisions. However, the difference between the usual scenario and the Glauber-like simulation, hence the difference betWeen the dynamical simulation and Glauber theory,can not be ignored. The sensitive effect of the hadron formation bine on the J/ψ suppression is studied in detail. The results seem to denote that for the J/ψ suppression the meson absorption plays a role in pA as well as in BA collisions.
Future electron linacs require high gradient acceleration. In this paper, the studies on the high shunt impedance backward traveling wave electron linac accelerating stature (BTW) are presented. At first, the characteristics of BTW are researched. The option of mode and optimal design methods of ascelerating cavity for BTW are stUdied. A Physical design method for BTW accelerators, including longitudinal and transversal particle dynamics, is given. Based on above studies, a 9MeV BTW accelerating tube at 3π/4 mode with frequency 2856MHz for inspechng large container as radiation source at customs is designed, and a comparison with disk-loaded wavegulde accelerating tube is made. The result of research leads to the conclusion that backward traveling wave accelerating struture is preferable. Because BTW has higher effechve shunt impedance, shoder filling bine and more stable operation.
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