1996 Vol. 20, No. S3
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The method for particle identiHcation using dE/dx information from the BES large cylindrical drift chamber is briefly described. The performance of the particle identiHcation using dE/dx is given. After applying systematic effect corrections and absolute energy calibration to the dE/dx raw data, the dE/dx resolution of 7.5% is obtained for minimum-ionizing particles (0.4-0.5GeV/c 7π) with more than 30 dE/dx samples per track. This results in 3σK/π separation for momentum up to 0.65GeV/c and 3σe/π separation in a momentum range of 0.2 ≤ p ≤ 4GeV/c.
The RIBLL1 terminal experimental setup consists of the RIB identification system, the secondary target chamber and target control system, and the secondary reaction products measurement system. The high-gain x-y position-sensitive PPAC with grouped delay cable readout, the scintillator for timing detector focused with an ellipsoidal surface, the traverse field IC, the large-area 2D position-sensitive scintillator with PMT matrix readout, the Compton suppressed HpGe γ-ray detectors, and the twin longitudinal field IC are its major components. To date,this setup has been installed at the RIBLL1 terminal. The performance measurements and test experiments are in progress.
The threefold massive fragment in hot nuclei with medium mass number has been measured in 40Ar+115In, 103Rh, and 93Nb reactions at 25MeV/u. The fragments emitted at angles larger than 32° are detected by ten parallel plate position-sensitive avalanche counters (PPAC), each with an area of 25×20cm2. The total kinetic energies (TKE),the yield ratio P32 of the threefold fragmentation to Hssion,and the distributions of the fragment mass, velocity, and relative angle,etc., are obtained. From the mass ratio of the fragments, a simple empirical expression is deduced. By analyzing their angular correlation function with a simple space-time model, the time difference between two scission points in the threefold process in the Ar+In reaction system is derived. A systematics of P32 versus Z2/A for hot nuclei is observed.
The high-spin states of 198Bi have been studied via the reaction 187Re(16O, 5n)198Bi at 16O energies from 85-105MeV. In-beam measurements of γ-ray excitation functions, γ-γ-t coincidences, and γ-ray angular distributions were carried out with 6 BGO(AC)HPGe detectors and 1 intrinsic Ge planar detector. A level scheme for 198Bi with 26 γ-rays was established for the first time, including a 15+ isomer with a measured half-life of 8.0±3.6ns. Based on the known level structure systematics in 200-206Bi, the level structure of 198Bi was qualitatively interpreted by using semi-empirical methods.
The relations between L± operators and the generators in the quantum enveloping algebras are studied. The L± operators for UqAN and UqG2 algebras are explicitly expressed by the generators as examples.
The two-point function of the 0++ three-gluon scalar current is calculated in including not only the perturbative contribution but also the nonperturbative ones resulted from condensates of dimensions up to six. In a typical "resonance plus continuum" model of the spectral function of the current, the quantum chromodynamics sum rules for the 0++ three-gluon scalar glueball are deduced, and the mass of that glueball is determined to be approximately 1.45GeV.
The multiparticle correlations of pions emitted from sources with different degrees of coherence are simulated by the Monte Carlo method. The sensitivity of the dependence of the multipion correlations in subevents with different multiplicities on the degree of coherence of the pion-emitting source is investigated. The degrees of coherence of the sources for central collisions of 2.1AGeV Ne+Pb and 1.2AGeV Ar+KCl at the Bevalac streamer chamber are analyzed. The results are compared with previous two-pion interferometry results.
The relaxation of the isoscalar giant monopole resonance (GMR) in the hot nuclei produced in heavy-ion reactions is discussed based on the Boltzmann-Nordherin-Vlasov equation. The oscillation of the GMR in the spherical hot nuclei is isotropic. The GMR energy calculated is approximately equal to that resulting from the formula EGMR=80A-1/3. The nucleon collision and the particle escape are the dominant reasons for the relaxation of the GMR in the hot nuclei.
With the aid of the theoretical few-body method, the binding energies of the double ∧ hypernuclei ∧∧5H, ∧∧5He, ∧∧4H and ∧∧4He are calculated. The results show that a stable bound state of ∧∧5H or ∧∧5He exists definitely with the double ∧ binding energies B∧∧(∧∧5H)=6.75MeV, and B∧∧(∧∧5H)=7.67MeV, respectively. As to ∧∧4H, the preliminary results manifest that it has a bound state but unstable against the decay to the ∧3H+∧ channel. No bound state exists for ∧∧4He.
The Gamow-Teller transitions are systematically investigated for nuclei with A=147-153 in terms of the shell model. These nuclei have only the Gamow-Teller decay channel π1h11/2→vlh9/2. The overall comparisons of the experimentally reduced probabilities Bexp(GT) with the calculated probabilities Bcal(GT) show that there is a quenching factor γ2 with optimum value 0.17±0.05 in this mass region.
A bunched beam for a free-electron laser (FEL) driven by a linac (i.e., linear accelerator) always encounters some beam-pipe size changes in its transport process. In this paper, the formulas are derived for calculating the equilibrium field energy and the difference of a bunched beam in two pipe sizes by using a space-charge cylinder model. The calculations show that the results of the space-charge cylinder model are significantly different from those of continuous beam model previously used.
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