1997 Vol. 21, No. S2
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The structure, operation principle, and performance of the bi-dimension position sensitive avalanche chamber (BPAC) used in the study of fusion fission induced by heavy ions at the near- and sub-barrier energy regions are described.
The fold angle distribution of fragments in different angle regions for the 84 MeV (Ecm) 16O+232Th reaction system was obtained by using BPAC, from which the angle distribution of transfer-fission fragments has been distinguished from that of compound nucleus fission fragments. It is thereby certified that transfer Hssion is not the reason for anomalous anisotropies of fragment angular distribution. Meanwhile experimental results supported the pre-equilibrium fission model, in the frame of which the anomalous anisotropies of fragment distribution were explained.
Decays of the J/ψ resonance into the three-photon final state are investigated. Branching ratios for the decays of J/ψ→γπ0 and J/ψ→γη' are determined to be Br(J/ψ→γπ0)=(4.6±1.1)×10-5 and Br(J/ψ→γη')=(4.12±0.82)10-3. The ratio of the two decay widths, Γ(J/ψ→γη')/Γ(J/ψ→γη),is 4.79±0.85. This value agrees weM with the predictions of the two theoretical models.
High-spin states of 162Lu have been produced and studied via the 147Sm (19F,4nγ) 162Lu reaction. In-beam γ-rays were measured by using 1 planar detector and 7 high-purity Ge detector with BGO anti-Compton shield. The level scheme of the yrast band in 162Lu was established for the first time and the signature inversion in energy was discovered at the low rotational frequencies. The yrast bands of doubly odd nuclei in the A=160 mass region have been reinvestigated and the systematics of signature inversion is briefly discussed.
This paper supposes that all cosmic ray (CR) particles of energy below 3×1018eV mainly originate and accelerate in an individual explosion of the supernova (SN) in the Galaxy; with the use of an isotropic diffusion propagation model, the non-steady state density distribution of Iron nuclei is investigated. Considering the effect of extragalactic CRs and the variety of the galactic CR nuclei, the statistic model of galactic CRs with a reasonable distribution of the galactic SNs in space and time can account for the spectrum of CRs in the energy range of 1012-1020eV quite well.
The paper describes the structure and performance of the phoswich telescope made of 1 mm thick scintillator NE102A and 40 mm thick CsI(Tl). The front area of the CsI(Tl) is 24 mm×24 mm and back area is 37 mm×37 mm. The Z=1 isotopes p, d, t, and all other detected fragments have been separated clearly by using the traditional fast-slow gate QDC method.
The incomplete-fusion-fragmentation model is used to analyze the fragmentation of the projectile remnant in the 600 MeV/uAu+Au reaction. The theoretical results of the mass number, the excitation energy, and the thermodynamic temperature of the projectile remnant agree well with experimental data. The backbending structure in the curve of temperature as a function of the excitation energy per nucleon, i.e., the evidence of liquid-gas phase transition, is reproduced and related to the decay mode transformation from the dominance of the multifragmentation mode to the vaporization mode.
The thermalization, expansion, and radial flow in the processes of intermediate energy heavy ion collisions are discussed via the BUU model. From the calculation of quadrupole momenta and density distributions, it is shown that the global equilibrium is reached for the collision system at lower energies, while at higher energies only the local equilibrium could be reached. Using the Skyrme interaction, the influences of radial flow on the equation of state are also studied, which shows that radial expansion flow Is sensitive to the effective mass, but insensitive to the incompressibility.
The ground state properties of the nuclei near Z = 8 and Z = 50 are investigated by the Skyrme-Hartree-Fock approach with new force parameters SKI2, SKD, and SKI4. Calculations show that the Skyrme-Hartree-Fock theory with the above force parameters provides a good description of those isotopes. Of the three sets of force parameters, SKI4, which has taken into consideration the isospin-dependence of the spin-orbit force, is the best one. SKI4 is also successful In reproducing the charged isotopes shifts near Z = 50.
With a density-, temperature-, and momentum-dependent mean field, five different phases of nuclear equation of states (gas, liquid, super-heated liquid, super-cooled gas, and mechanical instability of the spinodal phase) for 197Au are described. After performing a simulation in coordinate space and in momentum space for these different phases at finite temperature T=6 MeV, all kinds of nuclear clusters are sorted by using the coalescence model. The correlation analysis of the nuclear clusters demonstrates that the muitifragmentation pattern only conies from the mechanical instability of the spinodal phase.
A simulation of the electron cooling process for the heavy ion beam in the proposed HIRFL cooler-storage ring (HIRFL-CSR) is performed by taking into account the betatron and synchrotron oscillations of single particles. The continuous evolution of ion beam emittances and relative momentum spread are given. Some factoid that influence the cooling time, like the space charge effect of the electron beam, the dispersion in the cooling section, and the electron beam transverse temperature are presented.
In this paper, the design, simulation, and experimentation of a multi-cavity RF gun with a thermionic cathode for BFEL is described. This RF gun consists of 1/2+3 cavities with an on-axis coupling structure operated in the π/2 mode at 2856 MHz. We shorten the first cavity and add a short drift section between the second and third accelerating cavities, so that the power of back bombardment is decreased significantly and the longitudinal properties are adjusted properly.
A novel multi-cavity RF thermionic gun with very weak back bombardment effects has been designed, manufactured, tested, and subjected to experimentation. In this paper, we focus on the experimental results of this RF gun. From the current pulse shapes of BCT at the gun exit and the energy spectra at different positions of the macro-pulse, we can see that the back bombardment effects are suppressed greatly. A current of about 200 mA, a maximum electron energy of 1.8 MeV and a geometric RMS emittance of about 20-30 πrmm·mrad are obtained at the entrance of the linac.
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