2004 Vol. 28, No. 12
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Experimental data of complex cluster radioactivity (14C 34Si) are systematically analyzed and investigated with different models. Experimental half–lives are well reproduced with a factor of 5. A new linear relationship between the decay energy of cluster radioactivity and the number of α–particle in the cluster is found. This shows that the data of cluster radioactivity provide the first experimental evidence of α–condensation near the surface of heavy nuclei.
using the method of QCD factorization, we analyse the two–body non–leptonic decays of Bs meson into two light vector mesons in the standard model. We find: (i) non–factorizable corrections to different helicity amplitudes are different, and effective parameters ah_i are helicity dependent. (ii) the branching ratios of some Bs→vv channels are very large, and even reach to the order of 10-5, which is quite possible to be measured in the future experiments of b physics. (iii) for most decay modes, the transverse decay rate to the total one,Γ_t/Γ, is very small, which implies that both final state light vector mesons in the Bs→vv decay tend to zero helicity.
These years the RIBLL(Radioactive Ion Beam Line in Lanzhou) group have measured many nuclei's total reaction cross sections,which is the most popular and simple way to identify the exotic nuclei. The experiments were completed by using transparency method. The experimental results of different nuclei at different energies were converted into the same energy (30MeV/nucleon) and same target (silicon) by shen's formula. With comparing to their neighbors, we found that 9C,11Be,14Be,8B,14B and 12n's results show larger ones. The glauber model was used to calculate the total reaction cross sections, and 2-para-Fermi density distribution was introduced. For the exotic nuclei, a core plus exotic nucleons density distribution was used. The theoretical results are consistent with the experimental ones.
the cross section of Ω+Ω→(ΩΩ)_ 0++σ(ε) is studied by using an effective Hamiltonian method. the results show that the scalar meson production cross sections are about 1 to 2 order larger than those of the pseudo–scalar mesons or vector mesons, so the scalar meson production might be an important process for (ΩΩ)_ 0+ production.
the method of combinative track reconstruction with the hits in main drift chamber and vertex chamber at besⅡ detector is described, and the corresponding calibration method is also given. checked by experimental data and monte carlo generated data, the results show that the correctness and reliability of these methods have been proved, and the momentum resolution for charged particles has been improved by more than 20%.
A total of three beam lines, E1,E2 and E3 have based on the LINAC of BEPC. The E1 beam is to be used for intense slow–positron facility. The E2 is a primary positron or electron beam with an energy of 1.3—1.5GeV. the E3 is a secondary electron or pion test beam with a momentum can be adjustable continuously. The position accuracy of a detected particle is 0.2—0.4mm with an event rate of 3—4Hz.This beam has been successfully used for some detectors beam test.
We have synchronized a 102MHz ultrafast self–mode–locked Ti:sapphire laser to a 2856MHz rf source with the sample–locking technology. The relative root–mean–square time–jitter is 0.57ps and the maximum time jitter is 2.60ps.This is the first time to accomplish the synchronization between the ultrafast laser pulse and the s–band microwave in china.Potential applications include synchronization of lasers and RF power sources in particle accelerator experiments and high–resolution pump–probe experiments.
The deflecting angles of X-ray beams caused by refractive objects are deduced according to the refractive process at interface of different refractive indexes. The spacial resolution and the electron density resolution of the diffraction enhanced imaging (DEI) method are discussed relating to the experimental parameters. Appearances of refractive contrast in the DEI method are discussed and experimentally confirmed. Vivid images of blood vessels in human liver sample are obtained by DEI technique using X-rays with different energies. The contributions of the refractive contrast in improving the image contrast are easily understood.
Recent works on the relativistic description of exotic nuclei and nuclear matter at extreme conditions are reviewed. New effective interactions, PK1, PK1r and PKDD in the relativistic mean field(RMF)theory, are proposed with the center-of-mass correction included in a microscopic way. They are able to provide an excellent description not only for the properties of nuclear matter and neutron stars, but also for the nuclei near or far from the beta–stability line, including halos and giant halos at the neutron drip line in nuclei and hyper–nuclei. Based on the solution of the RMF equations, good spin symmetry is found in anti–nucleon spectra.
An application of the pseudo-SU(3) shell-model to 162Dy illustrates that complex many–body behavior in atomic nuclei can be given a simple geometrical interpretation.
Giant monopole resonances(GMR) are studied using a recently developed relativistic mean field theory computer code. We calculated the GMR energies of 16O, 40Ca and 208Pb for both the isoscalar and isovector cases. Good agreement with experimental data is obtained.
random one plus two–body hamiltonians invariant with respect to o(n_1)o(n_2)symmetry in the group–subgroup chains u(n )u(n_1)u(n_2)o(n_1)o(n_2)and u(n )o(n )o(n_1)o(n_2) of a variety of interacting boson models are used to investigate the probability of occurrence of a given(ω_1ω_2)irreducible representation(irrep)to be the ground state in even–even nuclei;[ω_1] and [ω_2] are symmetric irreps of o(n_1) and o(n_2) respectively. employing a 500 member random matrix ensemble for n boson systems (with n=10–25),it is found that for n_1,n_2≥3 the (ω_1ω_2)=(00) irrep occurs with～50% and (ω_1ω_2)=(n0) and (0n) irreps each with～25% probability. similarly,for n_1≥3,n_2=1,for even n the ω_1=0 occurs with～75% and ω_1=n with～25% probability and for odd n,ω_1=0 occurs with～50% and ω_1=1,n each with～25% probability. an extended hartree–bose mean–field analysis is used to explain all these results.
The quark mean field model, which describes the baryon using the constituent quark model, is applied to study the properties of finite nuclei and hypernuclei. The meson mean fields couple directly with the quarks and change the properties of baryons in nuclear medium. The quark mean field model provides satisfactory results on the properties of spherical nuclei and hypernuclei. it also predicts an increasing size of the nucleon as well as a reduction of the effective mass in the nuclear environment.
in this paper we briefly review the fusion process of very heavy nuclear systems and some theoretical models. We propose a microscopic transport dynamic model, i.e. the improved Quantum Molecular Dynamic model, for describing fusion reactions of heavy systems, in which the dynamical behavior of the fusion barrier in heavy fusion systems has been studied firstly. We find that with the incident energy decreasing the lowest dynamic barrier is obtained which approaches to the adiabatic static barrier and with increase of the incident energy the dynamic barrier goes up to the diabatic static barrier. We also indicate that how the dynamical fusion barrier is correlated with the development of the configuration of fusion partners along the fusion path. Associating the single–particle potentials obtained at different stages of fusion with the Two center Shell Model,we can study the time evolution of the single particle states of fusion system in configuration space of single particle orbits along the fusion path.
In this work, the vector meson exchange effect in NN interaction is studied on quark level in the extended chiral SU(3) quark model. The π,ρ and ω–meson exchange GCM potentials of central force and NN scattering phase shifts for all scattering partial waves are given. It shows that the vetor meson exchange potential can substitute one–gluon exchange (OGE) potential to explain repulsive core of the NN interaction.
The problems related to the modeling of quark confinement and Goldstone boson-quark coupling in the prevailing constituent quark models are discussed based on the lattice QCD result and the chiral symmetry spontaneous breaking theory.
Evidence for a narrow baryon state is found in quasi–real photo–production on a deuterium target through the decay channel K0sp→π+π–p. A peak is found in K0sp invariant mass spectrum at 1528± 2.6(stat.)±2.1(sys.)MeV,which can be interpreted as the predicted Θ+(uudd)pentaquark baryon state. The absence of peak structure in K+p invariant mass spectrum implies that the state is very likely a isosinglet state.
The results of relativistic mean field (RMF) calculations are presented for some of strange, charmed and bottom hypernuclei and compared to each other. The calculation includes single particle energies and other static properties of hypernuclei with different flavours. The potential well depths and coupling constants of these flavoured baryons are estimated and the results show rich behaviour. A search for charmed hypernucleus with atomic number A≥100 is suggested. Possible influences of different baryons impurities on the core nucleus are also examined.
The isospin effect in central and peripheral heavy–ion collisions at intermediate energies is studied by means of improved quantum molecular dynamics and isospin dependent quantum molecular model. it is shown that the influence of the density dependence of the symmetry potential on the average N/Z ratio of the products in central and peripheral reactions exhibits different character due to the different mechanism of particle emission. We find that the average N/Z ratio of emitted nucleons in neutron–rich heavy ion collisions is sensitive to the symmetry potential for both central and peripheral cases. furthermore, for peripheral neutron–rich heavy ion collisions, the N/Z ratio of intermediate mass fragments is also sensitive to the density dependence of the symmetry potential,which provides us with a useful probe to the symmetry potential.
the nuclear processes in astrophysics are briefly reviewed, and the explosive hydrogen burning are addressed and calculated with some new reaction rates obtained from the most recent experimental data. We pointed out that the reaction flux from the hot pp–chain into the CNO cycle through the proton capture on 11C may overcome the flux through the 3α process. the abundance of 18F calculated with the new rates of the 18F(p, γ) and (p,α) is 1.8 times larger than the previous one. The calculated results of the rp–process at the typical condition of the X-ray burst show that the abundances of the waiting point nuclei 89Ru and 93Pd, using the recent experimental β–decay life times, are about 4 times larger than the previous ones.
The quantum vacuum in a many–body system of finite nuclei has been investigated within the relativistic Hartree approach which describes the bound states of nucleons and anti–nucleons consistently. The contributions of the dirac sea to the source terms of the meson–field equations are taken into account up to the one–nucleon loop and one-meson loop. the tensor couplings for the ω–and ρ–meson are included in the model. After adjusting the parameters of the model to the properties of spherical nuclei, a large effective nucleon mass m*/m_n≈0.78 is obtained. the overall nucleon spectra of shell–model states are in agreement with the data. The computed anti–nucleon spectra in the vacuum differ about 20—30MeV with and without the tensor–coupling effects.
There are two methods to take account of the contribution of negative energy states in the relativistic random phase approximation. One is due to Dawson and Furnstahl. They made the ansatz that the dirac sea is empty. The other is the Dirac hole theory, which postulated that the sea should be fully occupied. The two methods seem contradictory concerning the way through which the negative–energy states contribute. The relation between the two theories is studied and the conditions under which the Dawson-Furnstahl theory is a good approximation to the Dirac theory are enunciated.
the microscopic mechanism of the identical bands in odd-odd nucleus 194Tl and its neighbor odd-A nucleus 193Tl are investigated using the particle–number conserving (PNC) method with monopole and quadrupole pairing interaction. It is found that the blocking effect plays an important role in the variation in moments of inertia (J(1) and J(2)) with rotational frequency for the sd bands and identical bands. And the angular momentum alignment i(ω) of the six SD bands in 194Tl relative to the 193Tl(1) also is discussed.
A Nilsson mean–field plus extended pairing interaction Hamiltonian with many–pair interaction terms is summarized. The investigation shows that one–and two–body interactions continue to dominate the dynamics for relatively small values of the pairing strength. As the strength of the pairing interaction grows, however,higher many–body interaction terms grow in importance. As an example, numerical fits to even–odd mass differences in the 154—171YB isotopes shows that the new model is applicable to well–deformed nuclei.
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