1998 Vol. 22, No. 8
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131Pm nucleus was produced in the 106Cd (32S,3p4n) 131Pm reaction. Theproducts were transported by helium jet and tape system, and X,γ single spectra and X-γ,γ-γ coincidence spectra were measured. The half-life of 131Pm has beendetermined to be (6.3±0.8)s. A partial decay scheme of 131Pm is proposed.
The emission time of intermediate mass fragments has been studied as afunction of spatial evolution of the source for 40Ar+159Tb reaction at 30 MeV/u.Reduction of the mass number of source has a very small effect on the extractedemission time. For the high-energy fragments with a short emission time ≤100fm/c,a smaller nuclear density would lead to a smaller assignment for, therefore thevalues extracted in the normal nuclear density could be taken as upper limits of realvalues. For the low-energy fragments, their emission times do not vary with size ofthe source and these values could be taken as real values.
Fragment-fragment conelation functions have been measured in E/A=30 MeV 40Ar+natAg reaction via the technique of intensity interferometry. Emission times of intermediate mass fragments have been extracted from reduced velocity correlation functions by using the threebody trajectory model. The average emission time of intermediate mass fragments varies with the energy of fragments. It decreases from about 300fm/c for low energy fragments to about 80fm/c for energetic fragments. After subtmcting the contribution of projectile-like fragments, average emission times of mid-rapidity fragments are of the order of 250fm/c for this reaction.It indicates that intermediate mass fragments emitted in this reaction mainly come from sequential binary decays.
Hadronization at finite temperature and density is discussed in the framework of the Nambu-Jona-Lasinio (NJL) model. The differential cross-section for the conversion of a quark-antiquark pair into two pions to the first order of 1/Nc expansion is calculated as a function of the c.m. energy s, temperature T and the chemical potendal u. The density effect is emphasized.
The particle multiplicity difference between heavy quark hadronic events and light quark ones is calculated by color dipole model. The results agree well with experments. The comparison of the results with PQCD model and naive model is presented.
In ordor to test the two-boody correlation transport theory (TBCTT), which is established for heavy ion collisions based on the two-boody correlation dyanmics, detailed comparisons between the preliminary numerical results of TBCTT and those of quantum molecular dynamics (QMD) am performed, and it is shown that all behaviors of quantites studied for different incident conditions of heavy ion collision are very similar for two theories. This implies that the TBCTT theory is promising for the description of heary ion collision dynamics with selfconsistent inclusion of fluctuation effects.
Based on the dualigy that both the inelastic and resonance physics language work for the explanation of nucleon polarized structure functions at moderate Q2, the higher-twist effect on the nucleon g1 is predicted.
The SU(3) chiral quark model is used to invesdgate the structures of three six-quark systems-H dibaryon d' and d' states. The non-perturbative QCD effects such as SU(3) chairl field coupling and the vector-coupling effect on the confinement potential are studied. The results show that the SU(2) chiral field coupling makes six-quark system more stable, but the SU(3) chiral"cloud" is not favourable to form the dibaryons.
In the nuclear medium, there are the non-nucleonic components. The leak-out panons, which form some colour-singlet parton clusters, are the origion of the non-nucleonic components. Meanwhile, the small x partons become co-used by several nucleons because the pamons' longitudinal size extends over more than one nucleon. The nucleon effective mass can be successfully used as the only free parameter to adjust the sbucture function ratios recently measured by NMC.
Two kinds of siganttre splittings, the △I=1 staggering and the band head splitting, are studied in odd-A superdeformed nuclei in the A-190 mass region. It is shown that the band bead splittings exist in the signature partner bands of some odd-A superdeformed nuclei by means of analysing the experimental M1 transition energies between the partner bands. A possible mechanism is proposed for this phenomenon.
The impedance of Beijing Electron positron Collider (BEPC) is studied in detail, and the possibility of suppressing bunch lengthening in BEPC is discussed in the view of decreasing the coupling impedance.
This paper discusses the collision of heavy ions with residual gas atoms in the vacuum and the cross-sections of the collision processes. Tlhe method calculating beam transmission efficiency in vacuum is presented taking HIRFL and CSR machine as examples. Based on rich experimental data a series of empirical formulae of calculating the cross-section of charge changing process is given. The transmission efficiency curvcs of different sections in HIRFL and CSR are also calculated, and thus the reasonable requirements for HIRFl and CSR vacuum systems ue given. The calculation method has been checked by the measurements of vacuum and beam loss in HIRFL.
The changes of focusing structure parameters caused by the DC-clearing electric field of storage ring were researched. The conclusion is made that tune shift caused by the DC-clearing electric field is related to the real-time close orbit of stored beam. The clearing electric field asymmetrically distributed along the ring destroys the symmetry of the focusing structure and decreases the acceptance of storage ring. It has negative effect to the injection and accumulation process in certain condition.
The experimentd study of synchrotron radiation X-ray interference has been presented. This experiment has been performed at the topography station of Beijing Synchrotron Radation Facility. The Moire fringes have been observed on the X-ray films. It has laid an initial foundation for the measurements with nm length.
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